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Section IIIORGANS


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153

Chapter 12Kidney, Ureter, and Adrenal Glands

My reynes or Kidneis, hath chiden me unto the night.MORE

Picus Wks. 20/1, 1510.

That the watry humour may be separated from the blood, Naturehath added the Reins to the rest of the bowels.

N. CULPEPERCulpepers Last Legacy. London, N. Brook, 1661.

DEVELOPMENT OF THE KIDNEY,URETER, AND ADRENAL GLANDS

Development of the KidneyNephrogenic Cord and Pronephros

212weeks

In each somite,the intermediate cell mass of mesodermaltissue, the intermediate mesoderm,develops at the junctionof the amnionandyolk sac,a region medial to the commu-nicationbetween the intraembryonic and extraembryonicceloms (Fig. 12-1A).

312weeks

The intermediate mesoderm that lies caudal to the intraem-bryonic celom forms the nephrogenic cord (urogenitalridge), from which the embryonic kidneys, gonads, andmesonephric (wolffian) ducts arise.

Pronephros

Three sets of kidneys develop from the intermediate meso-derm during human embryogenesis. The pronephros isrudimentary, the mesonephros is provisional, and the meta-nephros becomes the permanent kidney (Fig. 12-1B).

The rudimentary pronephros in humans is not clearly de-marcated from the mesonephros because it is made up ofsmall aggregations of cells, the nephrotomes, which arise fromstalks in the nephrogenic cord of the seven cephalad somites.

The nephrotomes are drawn into hollow tubes to formnephroceles, which in turn interconnect to join the primaryexcretory duct. Although the pronephros is not functionaland will degenerate, the tubular portions become part ofthe primary excretory duct (the mesonephric or wolffianduct) that grows caudally to empty into the cloaca.

A

B

FIGURE 12-1.


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SECTION III ORGANS154

Mesonephros

The mesonephros, like the pronephros, is formed in theintermediate mesoderm from the nephrogenic cord. As themesonephros grows, it expands into the body cavity as partof the urogenital fold,which will later contain the mllerianduct and reproductive gland (Fig. 12-2). The fold will

become divided longitudinally into a genital fold and a me-sonephric fold and be partially separated from the bodywall by the formation of a mesentery. The genital portionsubsequently acquires its own mesentery, the mesovarium ormesorchium. Mesodermal cells, beginning cranially, aggre-gate within the cord to form vesicles that elongate into 40or more mesonephric tubules.One end of each tubule con-nects with the mesonephric duct,and the other invaginatesto become the glomerular(Bowmans) capsule.The meso-nephric nephrons degenerate, starting from the cranialend, leaving only a few caudal remnants in the male.

The dorsal aorta supplies blood to the mesonephrictubules, and thepostcardinal veinsprovide venous drainagefrom them as well as the caudal body wall and the neuraltube (see Figs. 1-2 and 2-6).

Mesonephric Duct and Ureteric Bud

The mesonephric (wolffian) ductdevelops caudally, so thatby 4 weeks it joins the cloaca.

After the urogenital sinus separates from the rectum,the mesonephric duct will form the superficial part of the

trigone. In the male, it contributes to the formation of theepididymis, vas deferens, ejaculatory duct, and seminalvesicle. In the female, it degenerates, leaving only vestiges.The derivations and homologies of the urogenital organsare shown in Table 12-1.

About the middle of the fifth week of gestation, themesonephric duct develops a single branch, the ureteric

bud,where the duct bends at a right angle at the termina-tion of the common excretory ductproximal to its junctionwith the cloaca(Fig. 12-3).At first, the bud grows from thedorsolateral surface toward the spine and then turns crani-ally until it meets the mesenchyme of the caudal portionof the nephrogenic ridge, the metanephric blastema.Thisregion of the nephrogenic cord had separated earlier. Atthe level of the second lumbar vertebra, the mesenchymalmass blocks further ascent of the bud. As the body length-ens and the kidney ascends, the bud (now the ureter) keepspace. As it branches, it will eventually form the pelvis, caly-ces, and collecting tubules of the mature kidney. The stepsof development are outlined in Table 12-2.

At this time, the urorectal septumstarts to separate thehindgut from the urogenital sinus,a process that will endwhen the septum arrives at the cloacal membrane.

Divisions of the Ureteric Bud

During the sixth week, perhaps under the inductive stimu-lus of the nephric cap, the tip of the ureteric bud elongatescraniocaudally to form an ampullawith a central cavity, the

FIGURE 12-2.


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CHAPTER 12 KIDNEY, URETER, AND ADRENAL GLANDS 155

UROGENITAL HOMOLOGIES

TABLE

12-1

Precursor Male Organ Female Organ

Indifferent gonad Testis Ovary

Primordial germ cells Spermatozoa Ova

Sex cords Seminiferous tubules Follicular cells

Mesonephric tubules Efferent ductules, paradidymis,appendix epididymis

Epophoron

Wolffian (mesonephric duct Ductus deferens, seminal vesicles Gartners canal

Mllerian (paramesonephric)duct

Appendix testis (hydatid), prostaticutricle

Fallopian tube, vagina(part)

Upper urogenital sinus Bladder, prostatic urethra Bladder, urethra

Lower urogenital sinus Urethra Vestibule

Genital tubercle Penis Clitoris

Genital folds Penile urethra (floor) Labia minora

Genital swellings Scrotum Labia majora

primitive pelvis (Fig. 12-4A).As the ureter pushes cranially,the cap of blastema that will form the future renal paren-chyma moves away from its site at the end of the nephro-genic cord. Neurons entering the cap with the bud may alsoplay a role in renal morphogenesis.

The bud divides into paired primary branchesthat will

form the major calyces (Fig. 12-4B).

Each branch progressively divides into secondary branchesat the same time that the nephrogenic blastema proliferatesto cap the divisions (Fig. 12-4C).

The bud ultimately will branch 15 times. The earliest fourto six branches from the ureteric bud become incorporatedinto the growing renal pelvis. The next three to five branches

are the primary branches: the cranial pole branch, dorsal and

FIGURE 12-3.


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ventral central branches, and a caudal pole branch thatbecome incorporated into the two or three major calyces(Fig. 12-4D).Because the branches are not supported by neph-ric tissue, with the onset of urine formation, they will dilate toassume the shape of the pelvis and calyces. Branching occurswith greater frequency at the renal poles; thus, the organ elon-gates and becomes reniform. The next three to five secondaryand tertiary branchesform ampullae and become the minorcalyces. At this point, the renal parenchyma encroaches on thetip of each branch to form a papilla so that the final five toseven branchings are left to form the collecting ducts.

Minor Calyces

The fetal minor calyces, 14 in number at the most, are firstarranged in pairs, one facing anteriorly and the other poste-

riorly. However, at the upper pole, three pairs face superiorly,

and at the lower pole, two pairs face caudally. Each calyxdrains a single papilla. A longitudinal groove on the surfaceof the kidney indicates the line between the paired pyra-mids of collecting tubules based on this anteroposteriorcalyceal division. There follows a period of calyceal fusion:The anterior and posterior calyces in the upper and inlower poles fuse across the frontal plane of the kidney, andthe anterior calyces in the middle portion fuse with eachother, as do posterior calyces, leaving an average number ofeight or nine, with a range from 5 to 20. Papillae also fuse,especially at the poles, leaving two or more of them withinone calyx. The usual result is that the upper pole has threecalyces, which may be on a single major calyx with papillaryfusion or on two short minor calyces with three papillae oneach. The two pairs of middle calyces usually face anteriorlyand posteriorly, but each of the pairs may fuse, leaving a

single trunk. In the lower pole, less fusion occurs, usually

STEPS IN THE NORMAL DEVELOPMENT OF THE KIDNEYS

T

ABLE

12-2

Gestational Days Embryologic Event

22 Cloaca and pronephric duct present 24 Mesonephric (wolffian) ducts and mesonephric tubules develop28 Wolffian duct joins cloaca; ureteral bud emerges from it

32 Ureteral bud enters metanephric mesenchyme; common excretory duct(wolffian duct and ureter) opens into cloaca

37 Pelvis and primitive calices form44 Wolffian duct (caudal) and ureter (cranial) separately enter urogenital sinus

after division of cloaca48 Nephrons and collecting tubules are formed; urogenital membrane opens52 Formation of glomeruli63 Onset of renal function70 Degeneration of wolffian or mllerian ducts84 Urinary and genital tracts become joined in the male110 Mesonephros involutes

150 Appearance of ureteropelvic junction

A B

C

D

FIGURE 12-4.


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leaving two pairs of minor calyces. Thus, in the adult, thepelvis has two general forms. In one, the upper major calyxis long and slender and the lower calyx is shorter and wider,which represents the double-calyceal arrangement of Sykes.In the other form, the minor calyces tend to empty directlyinto the pelvis without intervening infundibula.

Fused pyramids forming compound and conjoined caly-

ces, in which the cone shape of the papilla is modified, arefound most often at the renal poles, where they are morelikely to be associated with intrarenal reflux.

Development of Lobes and Pyramids

Branching of the ureteric bud into calyces results in thedevelopment of lobes(ranunculi), each with a central calyxand peripheral tubules. In the 10-week-old fetus, only twolobes are seen, but the number increases with age. The capover the ureteric bud segregates itself into smaller caps lyingover each of the four to six first-order collecting tubulesthatform the individual pyramids.The lobes are separated bythe interlobar septa of Bertin, which are indicated bygroovesof fetal lobulation on the surface. Secondary andtertiary pyramids are similarly formed (Fig. 12-5).After thesixth branching, the tip of each generation of collectingducts joins the renal tubule with its attached glomerulusthat has developed in the adjacent nephrogenic mesen-chyme. The maximum number of branchings is 14, reachedby the 28th week, after which some disappear. Each of thesefetal lobes could be considered a separate kidney, similar tothe arrangement found in marine mammals.

Interlobar Septa

A double layer of connective tissue and a layer of less differen-

tiated cortex lie between the pyramids of each lobe to form aninterlobar septum or renal column of Bertin. Traditionally,these have been called columnseven though they do not havea columnar shape; septahas been proposed as a better term.

The surface lobulation seen in fetal kidneys persistingafter the age of 4 years is caused by bulging of the several

pyramids as the cortex grows between the relatively fixedinterlobar septa. It is often associated with extrarenalbranching of the arteries and an abnormal renal pelvis. Usu-ally, as the cortex fills out, the lobulation almost completelydisappears, although in half of adult kidneys, some residuallobulation is found, usually on the anterior surface. Thebasic lobar arrangement within the kidney persists, however,

except in the arrangement of the vessels.The number of papillae present in the developing

kidney is probably fixed at that number at the stage at whichurine formation begins and causes differentiation betweencalyx and collecting duct. The actual number of papillaefound in the adult kidney depends on the degree of subse-quent fusion between the pyramids.

Ascent of the Kidney

At 6 weeks, the lower margin of the nephrogenic ridge liesopposite the second sacral segment, well caudal to the levelof the lower lumbar segments, when it is reached by theureteric bud. The metanephros, which now can be called akidney, capped by a large adrenal gland, grows cephaladbehind the mesonephros to reach and pass ventral to theumbilical artery (Fig. 12-6A).It is at this stage that the upperand lower poles can be identified.

As the caudal end of the vertebral column straightensand that portion of the body grows during the sixth week,the kidney increases rapidly in size and rounds up tobecome shorter, enabling it to move away from the angle ofthe umbilical artery (Fig. 12-6B).It thus appears to ascend,so that at 6 weeks it lies opposite the 3rd lumbar vertebra.

By 8 weeks, the kidney assumes its adult level at the2nd lumbar vertebra (Figs. 12-6C and D). Thus, ascent is theresult of both renal and skeletal growth.

The renal pelvis at first lies anteriorly because the initialdirection of the ureteric bud was posterior, but duringascent, the pelvis is moved to a medial orientation as thekidney rotates. The upper pole moves laterally and thelower pole moves medially so that the kidney assumes amore upright position.

FIGURE 12-5.


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DEVELOPMENT OF THERENAL VESSELS

Because the kidney ascends mainly by differential growth ofthe body, it acquires an arterial supply successively from thesegmental mesonephric vessels as it moves cephalad relativeto the major vessels. The development of the renal vascula-ture is closely related to that of the mesonephros and adja-cent structures. Arteries enter the kidney from successivesources, and veins drain the kidney into nearby as well asdistant visceral and parietal pathways. Many variations are

found, as would be expected from vessels that develop fromevolving embryologic systems.

Arteries

At 412weeks, approximately 30 lateral branches develop assegmental arteries from the dorsal aorta, extending fromthe 6th cervical to the 3rd lumbar segments. The more cra-nial of these roots gradually degenerate as more caudalones develop to supply the urogenital(mesonephric) arte-rial rete. At this stage the mesonephrosas well as the gonad,adrenal gland, and ureter obtain their blood supply fromthis source. As the metanephrosdifferentiates into a kidney,under the influence of the ureterbranching from the meso-nephric (wolffian) duct, and rises with differential bodygrowth, it successively acquires the segmental arteries thatconnect the rete to the aorta (Fig. 12-7).Most of the rootvessels to the rete degenerate, leaving the kidney vascular-ized by a single enlarged branch, the renal artery. Accessoryarteries are not rare. Because arterial degeneration beginsat the cephalad end of the metanephros, the segmentalbranch to the lower pole is the one most likely to persist asan accessory vessel.

Although within the kidney the renal segmental arterieshave a constant relationship with the renal segments (seeFig. 12-71),infinite variations occur in their origin and site

of division in relation to the hilum (Figs. 12-8 and 12-9).The apical and lower segmental arteries may originate inde-pendently directly from the aorta, in which case the renalsegmental artery may supply a larger segment of the kidneythan it would if it were a branch of the main renal artery(Fig. 12-10).

Multiple Renal Arteries

Although they are anomalous, accessory renal arteries areevidence of the persistence of one or more of the segmentalmesonephric roots extending from the 6th cervical to the3rd lumbar segments, the more caudal of which once sup-plied the renal arterial rete. The five segments of the nor-mal kidney are each provided with an artery; thus, accessory

A B

C

D

FIGURE 12-6.

FIGURE 12-7.


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arteries may be considered to be normal arteries that havea more cranial or caudal origin. Such vessels may supplyeither pole of the kidney (Figs. 12-11and 12-12).

On the right side, persistent arteries may lie anterior orposterior to the vena cava, and on the left, they may actuallyenclose the renal vein. Some arise from the base of therenal artery or from the aorta. Extra vessels are found in

10 to 40% of autopsy cases, and vessels to the lower pole aretwice as common as those to the upper pole.

Apersistent segmental artery to the lower pole may pro-vide the origin of the gonadal artery,and one to the upperpole may also provide an adrenal artery. In addition to seg-mental arteries, smaller accessory arteries, usually multiple,may come from the inferior phrenic or from an adrenal artery.

Venous Anomalies

The renal veins develop from venous plexuses and passthrough a complicated evolution by formation and absorp-tion of the postcardinal, supracardinal, and subcardinalveins, which are involved in the formation of the inferiorvena cava. Venous maldevelopment provides a continuumfrom almost normal to frankly abnormal configurations.Should the renal vein or vena cava become occluded, thesepersistent embryonic transitional pathways can providealternative routes of drainage.

The veins do not follow the arterial pattern. In fact,those vessels that make up the venous complex develop at adeeper level than that occupied by the arteries, althoughnear the vena cava, the renal veins come to lie anterior tothe arteries.

The right renal vein rarely has tributaries, except forthe gonadal vein in a fifth of cases, but the left renal vein (avessel that embryologically could be considered a segmentalleft vena cava) always receives the adrenal vein and gonadal

Right kidney

Right renal artery Left renal arteryAorta

Left kidney

FIGURE 12-8. Magnetic resonance angiogram

transverse section, showing right and left renal arteriesarising from the aorta and supplying their respectivekidneys.(Image courtesy of Raj Paspulati, MD.)

Renalartery

Aorta

Anterior divisionof renal artery

Posterior divisionof renal artery

FIGURE 12-9. Three-dimensional magnetic resonanceangiogram, showing the divisions of the renal arteries.See also Figure 12-71.(Image courtesy of Raj Paspulati, MD.)

FIGURE 12-10. Contrast enhanced CT scan, transversesection, showing segmental renal infarction from renalartery thrombosis. (Image courtesy of Vikram Dogra, MD.)

Segmentalrenal

infarction

Normallyperfusedkidney

Thrombosed renal artery


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vein on that side, and most often has lumbar, ascendinglumbar, or hemiazygos communications. The reasons forthis difference may be found in the development of theinferior vena cava.

To understand renal and ureteral venous anomalies, itis necessary to review the development part of Chapter 2.The left renal vein from the hilum of the kidney to theends of the adrenal and gonadal veins is formed fromthe subcardinal vein, in addition to connection with the

residua of the intersubcardinal anastomosis. Also, as therenal vein crosses the midline it picks up the veins drain-ing adjacent organs and the lumbar veins. This complexorigin explains the greater length and larger number ofveins draining into the left renal vein compared with theveins on the right, where these tributaries drain directlyinto the vena cava.

The anomalies of the venous supply to the kidney thatresult from retention of embryologic pathways are describedin Figures 2-9 and 2-10. Most apparent clinically are the per-sistence of the left caval vein, the circumaortic venous ring,and the formation of retroaortic renal veins.

RENAL ANOMALIES

Renal Agenesis

Absence of the metanephros may be due to defects in thedevelopment of the nephrogenic ridge, but the usual find-ing in clinical practice is its absence from failure of forma-tion of the mesonephric duct and the ureteric bud. Thus,renal agenesis in the male is often associated with defects ofthe other derivatives of the duct. In 12% of males with asingle kidney, a genital abnormality is found, includingabsence, hypoplasia, or cyst formation of the seminal vesi-cle, vas deferens, and ejaculatory ducts. Important surgicallyis that the remaining kidney may be abnormal in formationor position.

In the female, genital anomalies are frequently associ-ated with renal agenesis (44%) because of the close develop-mental association of the mllerian duct with the wolffianduct at the urogenital sinus. The uterus may be unicornuate,bicornuate, or hypoplastic. The vagina may fail to form, or itmay be septate or even obstructed, resulting in unilateralhematocolpos. A syndrome is recognized secondary to inter-ruption of growth of the wolffian duct consisting of unilat-eral renal agenesis, absence of the fallopian tube, andabsence of half of the uterus. With bilateral absence of theducts, and thus absent kidneys, multiple anomalies associ-ated with oligohydramnios are the rule, including pulmo-nary hypoplasia, and the infant will show Potters facies(Fig. 12-13).

FIGURE 12-11.

Persistent segmental renal arteries

Dilated renal pelvis due to congenitalureteropelvic junction obstruction

FIGURE 12-12. Contrast enhanced CT scan, coronalsection, demonstrating the presence of persistentsegmental renal arteries, supplying the upper and lowerpoles separately. Patient also has dilatation of the rightrenal pelvis from congenital ureteropelvic junction

obstruction. (Image courtesy of Raj Paspulati, MD.)


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Duplex, Ectopic, and Horseshoe Kidneys

Renal duplication, the most common anomaly, occurs whenthe ureteric bud divides and two ureters enter the blas-tema (Figs. 12-14and 12-15).These kidneys have normalvasculature because the arterial distribution is not influ-enced significantly by abnormalities of the pelviocalicealsystem. In contrast, the rare supernumerary kidney that

results from a split of the nephrogenic blastema often hasabnormal vessels.

The anomalies of renal fusion and ectopiamay be placedin five categories: crossed with and without fusion, notcrossed with and without fusion, and fused caudally, thehorseshoe kidney.

Ectopiaoccurs when ascent is prevented at the time thatthe kidney lies at a level between the 3rd sacral and the2nd lumbar vertebra. Thus, there may be pelvic, iliopelvic,iliac, or lumbar ectopia (Fig. 12-16).Because arrest occursat a relatively early stage of embryologic development, ecto-pia is usually associated with incomplete rotation, a shortureter, and a blood supply that arises from local lateral seg-mental vessels, connections that account for the fixation ofthe kidney found at operation. In addition, anomalies of theexternal and internal genitalia and of structures associatedwith the cloaca are common. The typical pelvic kidney isusually smaller, lobulated, and of an abnormal (pancake-like) shape. The adrenal gland,however, is usually in a nor-mal position. At any level of arrest, the kidney, ureters, andassociated vessels will reside inside the envelope of the renal(Gerotas) fascia.

The kidney may be malpositioned from any one of thefactors responsible for its arrest; including malformation ofthe ureteric bud or of the metanephric tissue, or persistenceof the primitive segmental structure of the arterial system,although this condition is usually secondary. In addition,

FIGURE 12-13. Bilateral renal agenesis (Potterssyndrome). Autopsy study of a stillborn infantdemonstrating that neither kidney is present in theretroperitoneum. The white arrows indicate the

adrenal glands, which are typically large at birth, butdiminish by almost 50% by the 9th to 14th week afterbirth. (Image courtesy of Gretta Jacobs, MD.)

Duplexureter

FIGURE 12-14. Intravenous pyelogram,showing aduplex collecting system on the left. From this study,it is not apparent whether the ureteral duplication iscomplete or incomplete. (Image courtesy of VikramDogra, MD.)

FIGURE 12-15. Ureteral duplication. On the rightthere are two complete ureters, each draining separateportions of the kidney, and each with its own ureteralorifice in the bladder. In a setting of completeduplication, the orifice of the upper pole ureter issometimes ectopically placed, closer to the bladderneck, or outside the bladder proper (e.g., in the urethra,or even in the vagina in a female); this may result inobstructive changes in the renal segment drained by theanomalous ureter. (From MacLennan GT, Cheng L: Atlasof Genitourinary Pathology. Springer-Verlag London Limited,2011, with permission.)


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result from crowding in the pelvis by the large umbilicalarteries at the time that the blastemas would normallydiverge after passing them.

Horseshoe kidney occurs once in about 500 births,occurs twice as often in males as in females, and is themost common of the fusion anomalies. It probably out-numbers crossed ectopia by a ratio of 6 to 1. A wide variety

of associated anomalies are often seen, some of which maybe incompatible with life.

The pattern of the blood supply within each half of ahorseshoe kidney is usually the same as that of a normalkidney: Each kidney has single or double arteries angledcaudally. Each segment of the kidney is supplied by asegmental branch of the renal artery, without collateral con-nections between. Thus, within the renal substance the dis-tribution of blood is little different from that in normalkidneys.

The exception to a fully normal vascular pattern is thepresence of an artery to the lower segment. This vessel typi-cally has an abnormal origin, most often arising from theaorta at a level lower than the normal renal artery or fromthe common iliac artery or even from the internal iliacartery. Thus, an accessory artery may enter the kidney aboveor below the isthmus. If a substantial isthmusforms, it maybe partially supplied by an additional vessel arising from thecaudal part of the aorta or from the common iliac artery.

Malrotationis actually the result of arrest of rotation. Therenal pelvis remains in an anterior position, its orientationbefore ascent. However, the kidney may occasionally befound overrotated, so that the pelvis lies posteriorly.

No consistent embryologic explanation for these severalrenal anomalies is available. However, associated anomaliesof the genitalia and vertebrae are not unusual, suggesting acommon embryologic disturbance.

Ectopic rightkidney lying

above the liver

FIGURE 12-18. Coronal T2-weighted magneticresonance image. Same case as shown in Figure 12-17.The right kidney lies superior to the liver. (Image courtesyof Nami Azar, MD.)

Ectopic right kidney

FIGURE 12-19. Axial T2-weighted magnetic resonanceimage. Same case as shown in Figure 12-17.The rightkidney is in a superior location, but its exact location

was not evident from this study. Surgical explorationconfirmed that the diaphragm was intact; the rightkidney, although located superiorly, was notintrathoracic. (Image courtesy of Nami Azar, MD.)

FIGURE 12-20. Lump or cake kidney. This is a fusionanomaly somewhat similar to horseshoe kidney, but thefusion is more diffuse, rather than being localized to theinferior poles. Both ureters enter the bladder normally.(From MacLennan GT, Cheng L: Atlas of GenitourinaryPathology. Springer-Verlag London Limited, 2011, withpermission.)


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Left kidney

FIGURE 12-21. Crossed fused renal ectopia, demonstratedon sequential T2-weighted magnetic resonance imagesthat run from posterior to anterior in the coronal plane(see Figs. 12-22 to 12-24).This image demonstratesan empty right renal fossa. (Image courtesy of VikramDogra, MD.)

Normally situated left kidney

Crossed ectopic right kidney, fusedto lower pole of left kidney

FIGURE 12-22. A portion of the crossed fused ectopicright kidney becomes apparent on the left side. (Imagecourtesy of Vikram Dogra, MD.)

Left kidney

Crossed ectopic right kidney

FIGURE 12-23. The crossed fused ectopic rightkidney is more clearly evident. (Image courtesy of VikramDogra, MD.)

Crossed ectopic right kidney;left kidney is no longer visible

FIGURE 12-24. The left kidney is no longer apparent.(Image courtesy of Vikram Dogra, MD.)


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Isthmus between lower poles of right and left kidneys

Dilated renal pelves

FIGURES 12-25. Horseshoe kidney. Contrast-enhanced

axial computed tomography urogram in delayed phase,demonstrating a horseshoe kidney with contrast-filleddilated renal pelves, and an isthmus of tissue connectingthe lower poles of the two kidneys. (Image courtesy ofVikram Dogra, MD.)

Urinarybladder

Rightureter

Left renalpelvis

Right renalpelvis

Site of fusionbetween

lower poles

Left ureter

FIGURE 12-26. Horseshoe kidney. Three-dimensionalvolume reconstruction image, CT urogram, showingfusion of the lower poles of the right and left kidneys.Both kidneys appear to have dilated renal pelves andsome degree of caliectasis, suggesting impaired drainage.(Image courtesy of Raj Paspulati, MD.)

FIGURE 12-27. Horseshoe kidney. The two renal unitsare joined at their lower poles. One kidney showshydronephrotic changes due to obstructed drainage.(From MacLennan GT, Resnick MI, Bostwick D: Pathologyfor Urologists. Philadelphia, Saunders, 2003.)

Left renalvein

Left ureter

Tumor in upper poleof left moiety

Isthmus betweenlower poles

FIGURE 12-28. Horseshoe kidney, with a renal cellcarcinoma involving the upper pole of one moiety.The vessels and ureter have been isolated; the blueloop surrounds the renal artery. (Image courtesy ofRabii Madi, MD.)


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CYSTIC DISEASE

The development of cystic disease of the cortex depends ondeviation from the exact process with which the collectingduct must join the renal tubule. Disturbances in the connec-tion result in various forms of cystic disease depending onthe time of interference (Figs. 12-29 to 12-32).

FIGURE 12-30. Adult autosomal dominant polycystickidney disease. This is the most common geneticallytransmitted disease and the most common cystic renaldisease. When bilateral nephrectomy is performed insuch patients, the kidneys have often attained massivesize, as in this case. The cut surfaces demonstrate thepresence of innumerable cysts of variable size. Thecollecting system is normal. Despite distortion by thecysts, the kidneys retain a reniform shape. (Image courtesyof Pedro Ciarlini, MD.)

FIGURE 12-29. Infantile autosomal recessive polycystickidney disease. In this condition, both kidneys aremassively enlarged, which can impede lung developmentand result in stillbirth or death in early neonatal lifefrom respiratory failure. The kidneys retain theirreniform shape, and collecting systems are normal.Their cut surfaces have a spongy appearance becauseof the presence of innumerable small cystically dilatedstructures. (Image courtesy of Pedro Ciarlini, MD.)

Blind-ending proximal ureter

FIGURE 12-31. Renal dysplasia: multicystic kidney. Theterm dysplasiaconnotes arrested organ development,with persistence of structures that never completelydeveloped. Aplastic and multicystic dysplastic kidneysrepresent opposite ends of a spectrum, varying only inthe degree of cyst formation, which is variable. Aplasticdysplastic kidneys are extraordinarily small and exhibitvery limited or absent cyst formation, in contrast to themulticystic kidney shown here. In all instances, theipsilateral ureter is atretic or obstructed at the level

of the ureteropelvic junction. (Image courtesy of PaulGrabenstetter, MD.)

FIGURE 12-32. Bilateral renal dysplasia. Lower urinarytract obstructions, such as congenital bladder neckobstruction, posterior urethral valves, and urethralstenosis and prune-belly syndrome (which was theetiology of the bilateral renal dysplasia in this case),can result in dysplasia that involves both kidneys. (FromMacLennan GT, Cheng L: Atlas of Genitourinary Pathology.Springer-Verlag London Limited, 2011, with permission.)


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DEVELOPMENT OF THE URETER

Musculature and Luminal Development

Longitudinally oriented elastic fibers form in the adventitiaof the ureter at about 10 weeks, coincident with the onset ofthe formation of urine. These are followed by the appearance

of randomly oriented muscle fibers in the layer that will be-come the muscularis. The number of elastic fibers increaseslinearly with the thickness of the ureteral wall. In contrast tothe muscularis, those fibers associated with the submucosaare radially disposed. Fewer fibers develop in the lower ureterthan in its middle portion, a finding that might help explainthe occurrence of adynamic segments distally.

By 16 weeks, muscle extends the length of the extramu-ral ureter and, by the 36th week, involves the entire ureter,including the orifice. Muscle cells and, to a lesser extent,elastic fibers increase progressively to double their numberby the age of 12 years, either by multiplication of the exist-ing cells or by mesenchymal differentiation. The size of thecells also increases but to a lesser degree.

Into the early postnatal period, the muscle fibers arearranged more circularly but become more oblique withtime. By adulthood, the fibers have assumed the character-istic helical arrangement (see Fig. 12-83).

At first, the ureter has a lumen. Beginning at around512weeks, the lumen becomes occluded, first in the midpor-tion and, then by 7 weeks, is blocked proximally and distallyas well, events coincident with cessation of function of themesonephros. By 8 weeks, recanalization begins, extendingin both directions from the middle of the ureter, so that aweek later, the channel is open. Metanephric function is nota factor because it will not begin until the 10th week, butureteral lengthening may be a factor in clearance of the

obstruction. These observations may explain the greater fre-quency of ureteric valves in the proximal and distal segments,where delayed developmental arrest would be more likely.

URETERAL ANOMALIES

Most anomalies of the ureter occur either at the ureteropel-vic or the ureterovesical junctions. A rare exception to thisis the blind-ending ureteric bud, a blind-ending hollowstructure that joins the normal ureter at an acute angle, andthat is by definition at least twice as long as it is wide. Itswall structures are identical to those of the normal ureter(Fig. 12-33).Ureteral anomalies that occur in the uretero-vesical junctions are described in Chapter 13.

Congenital Obstructionat the Ureteropelvic Junction

Obstruction that occurs where the ureter joins the kidneymay be due to extrinsic factors, but more often, the cause isfaulty development.

Because the helical arrangement of muscle fibers neededfor urine transport develops progressively with time, arrest ofthis process would leave only circularly oriented fibers at thejunction, an arrangement more likely to be obstructive thanconductive. Alternatively, elongation of the ureter leaving

predominantly longitudinal fibers would likewise be a poorlyconducting arrangement. Other factors such as agenesis orreduction in fiber numbers would also leave a nonconduct-ing segment. It is clear that several factors are involved.Primary defects in programming the development of theureteric bud may lead to intrinsic, focal lesions such as ure-teropelvic junction obstruction or ureteral valves (Figs. 12-34to 12-36).

Extrinsic causes of ureteropelvic junction obstructionare usually an aberrant vessel or a band passing anterior tothe junction, although this may only contribute to intrinsicfactors (Fig. 12-37).Another cause may be reflux that over-loads a quasi-normal junction as urine returning to thebladder supplements newly secreted urine.

Retrocaval Ureter (see Fig. 2-9)

The postcardinal vein may remain dominant rather thangiving way to the supracardinal vein, or the periureteric ringmay persist. As the permanent kidney ascends, the postcar-dinal vein runs at first lateral and then medial to the kidney.As a result of the displacement and consolidation of theveins, the ureter lies dorsal to the vena cava.

Ureteral Valves

Several theories have been proposed for the origin of ure-teral valves, including failure of complete canalization aftera normal period of closure in the sixth week. They mayoccur when the axes of the lumina are eccentric so that theureter is overlapped at the site of the obstruction, resultingin a common wall, or they may result from persistenceof mucosal folds left over from the pleats formed duringureteral lengthening. Finally, they might arise if the ureterelongates faster than the kidney ascends.

FIGURE 12-33. Incomplete bifid ureter with a blindend. The ureteral outpouching is most likely a portionof a bifid ureter that failed to connect to the renalparenchyma; less likely, it may represent a truecongenital ureteral diverticulum. Both these entitiespossess a complete wall, including urothelium, lamina

propria, and muscularis propria. (From MacLennan GT,Resnick MI, Bostwick D: Pathology for Urologists. Philadelphia,Saunders, 2003.)


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Dilatedrenal

pelvis

Ureteropelvic junction

FIGURE 12-34. Congenital ureteropelvic junctionobstruction. The renal pelvis is distended, but the ureterbelow the ureteropelvic junction is of normal size. Therenal cortex appears scarred. (From MacLennan GT,Resnick MI, Bostwick D: Pathology for Urologists. Philadelphia,Saunders, 2003.)

Kidney

Distendedrenal pelvis

Renal vessel atureteropelvicjunction

Ureter

FIGURE 12-37. Congenital ureteropelvic junctionobstruction. Sagittal reconstruction image of contrast-enhanced computed tomography. This radiologic imageshows a blood vessel adjacent to the ureteropelvicjunction. It is a matter of debate whether such vesselscontribute significantly to the obstructive process.(Image courtesy of Raj Paspulati, MD.)

Remnant of large perirenal hematoma

Area of disruption in distended upper pole calyx

FIGURE 12-36. Congenital ureteropelvic junction

obstruction. Patient presented with flank pain andmassive retroperitoneal bleeding. He was found tohave ureteropelvic junction obstruction, with markedhydronephrosis of one half of a horseshoe kidney,treated by excision of the obstructed half of thehorseshoe kidney. The retroperitoneal hematomaappeared to be related to disruption of a thinned upperpole calyx (defect indicated by small wood sticks). Therewas no history of recent trauma. (Image courtesy of LisaStempak, MD.)

Ureteropelvic junction

Distended renal pelvis

FIGURE 12-35. Congenital ureteropelvic junctionobstruction. The renal pelvis is markedly dilated. Thechronically obstructed kidney shows pronouncedcaliectasis, loss of the renal pyramids, and thinning ofthe renal cortex.


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DEVELOPMENT OF THEADRENAL GLANDS

Fetal adrenals are very large during fetal life, especially inthe second trimester, mostly resulting from expansion ofthe cortical cells. They are still relatively large at birth,only to regress rapidly during the first 3 weeks of life (see

Fig. 12-13).During the eighth gestational month, the zonaglomerulosa appears, followed by the zona fasciculata atterm; the zona reticularis follows in the next 3 to 6 months,with the cortex completely differentiated by 2 years.

At birth, the large adrenal gland is vascular and easilyinjured during delivery.

Origin of the Adrenal Cortexand Medulla

Two separate tissues contribute to the formation of theadrenal glands, providing layers that remain distinct intoadult life (Table 12-3).

The adrenal cortexcomes from mesothelial buds on theupper third of the mesonephrosthat project into theprimi-tive celom with the gonad (Fig. 12-38). The buds form acellular aggregate on either side of the aorta. Some cellsmay not join the aggregation, accounting for accessoryadrenal cortical tissue about the adrenal gland and kidney,with the spermatic vessels or testis in the male and withinthe broad ligament and ovary in the female.

The adrenal medulla is derived from primitive ectoder-mal cells of the neural crest in the developing sympatheticnervous system (see Fig. 4-2). These sympathogonia nor-mally mature into sympathoblasts and ultimately intoganglion cells within the sympathetic ganglion. Alterna-tively, and of importance to the formation of the adrenal

medulla, they may migrate and differentiate into chromaf-fin endocrine cells, the pheochromoblasts, that will matureinto chromaffin cells after penetrating the adrenal corticalprimordium to form the adrenal medulla (Table 12-4).

Distribution of Fetal Chromaffin Bodies

In fetal life, the pheochromoblasts form chromaffin bodiesthat are distributed along the aorta, providing the mainsource of catecholamines (Fig. 12-39A).These cells migrateto and invade the adrenal cortical aggregation to form theadrenal medulla.

Some of these chromaffin bodies regress only partiallyafter birth and remain as theparaganglion systemdistributedwithin and adjacent to the prevertebral sympathetic gangliaand in the several sympathetic plexuses and ganglia (celiac,mesenteric, renaland adrenal, and hypogastric) as well as aplexus at the aortic bifurcation, the organ of Zuckerkandl(Fig. 12-39B).This system is a secondary source of catechol-amines throughout life and may become the tissue oforigin of pheochromocytomas. This is especially possible inchildren in whom 30 percent of pheochromocytomas are

extra-adrenal; they are not infrequently malignant.Two larger aggregates of chromaffin tissue related to the

superior hypogastric plexus, thepara-aortic bodies, remainon either side of the aorta in an inverted U-shape loopedover the inferior mesenteric artery. These bodies enlargeduring early postnatal life, only to virtually disappear atpuberty.

Adrenal Blood Supply

Arteries

The source of blood for the adrenal is the most cranial ofthe segmental mesonephric roots that once supplied theurogenital (mesonephric) arterial rete. Especially on theright side, smaller accessory arteries, usually multiple, maycome from the inferior phrenic or the renal arteries.

Veins

Resolution of the renal venous plexus on the right leaves asingle, short vein running obliquely that connects to theposterior surface of the vena cava. On the left, the residualleft subcardinal vein (see Fig. 2-7) is also single but oftenreceives blood from the inferior phrenic vein in addition tothat from the capsular veins. The left vein is longer anddescends vertically to join the renal vein.

ADRENAL DEVELOPMENT

TABLE

12-3

FIGURE 12-38.

Neuralcrest

Splanchnicmesoderm

Nephrogenicmesenchyme

Medulla Cortex


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ADRENAL ANOMALIES

At 8 weeks, the adrenal gland has migrated to lie adjacentto the kidney and will subsequently rise as the kidneyascends. However, the position of the adrenal gland is inde-pendent of that of the kidney, because with an ectopickidney, the adrenal gland is found in its normal position.

Agenesis may occur, often associated with renal agenesissecondary to failure of the entire blastema. Adrenal ectopiamay be found. Of surgical importance when operating on asolitary kidney is the rare possibility that the single adrenalgland lies under the renal capsule (Figs. 12-40and 12-41).Accessory adrenal cortical rests are found intra-abdominallyand retroperitoneally within abdominal and sexual organs(Fig. 12-42).As noted previously, extramedullary chromaf-fin tissue is commonly found and may become transformedinto a pheochromocytoma.

DEVELOPMENT OF THE PERIRENALFASCIAS

Development of the Strataof the Retroperitoneal Fascias

At first, a continuous sheet of mesenchyme lies between theepithelium of the skin and the mesothelium lining the celomiccavity, but as the muscles and skeleton develop in this space, theremaining mesenchyme becomes split into a subcutaneouslayer and a retroperitoneal layer. The subcutaneous layer dif-ferentiates into the dermis, superficial fascia, and deep fascia ofthe body wall. The retroperitoneal layer, as the retroperitonealconnective tissue, lines the body wall and surrounds the gastro-intestinal and urinary organs (Table 12-5)(see Fig. 8-4).

With maturation, three strata can be distinguishedin the retroperitoneal connective tissue. One is an inner

ADRENAL SYMPATHETIC DIFFERENTIATION

T

ABLE

12-4

Sympathogonia

Ganglioncells

Pheochromocyte(chromaffin system)

Accessorypheochrome tissue(paraganglia)

Medulla ofadrenal

Sympathoblast Pheochromoblast

A

BFIGURE 12-39.


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stratumembedding the gastrointestinal system. Beneath thislayer is the intermediate stratum embedding the urinarysystem that differentiates into dorsal and ventral layers inthe region of the kidneys.

Local conditions play a role in fascial development.Distinct fascial layers in the intermediate stratum form inareas of organ mobility, possibly resulting from shearingaction; they do not develop in the absence of the kidney.

The outer stratuminvests the inner layer of the body walland pelvis as the transversalis fascia and its extensions, the

endopelvic fascia, and terminates in continuity with theinternal spermatic fascia.

Fusion of the Colonic Mesenteries

In addition to a covering of primary retroperitoneum, thekidneys acquire a secondary coat from the fusion of thecolonic (and on the left, duodenal) mesenteries as the bowelrotates into its final position. The sequence of intestinal rota-tion is illustrated in Figure 6-5. At first, the dorsal mesenteryforms a barrier between the right and left sides as it runs thelength of the peritoneal cavity. Rotation of the intestinal loopbegins counterclockwise. The future ascending colon rotatesover the base of the mesentery, exposing the right side of itsmesentery. At the same time, the descending colon with itsmesentery merely rises into the left upper quadrant, thusmaintaining the original right and left orientation of the sur-faces of the original colonic mesentery.

As the left mesocolon meets the primary peritoneumon that side, its left side fuses with it, and the underlyingmesothelial layers disappear. This places the connective tis-sue of the inner strata of the mesentery (two layers) and theprimary peritoneum (one layer) in contact, forming athree-ply layer (shown in Figure 6-6). A layer so formed istermed fusion-fascia.*On the right, the left side of the me-socolon also fuses with the right primary retroperitoneum,

*Fusion-fasciais a thin membranous layer formed by the apposition of two mesotheli-ally covered surfaces of peritoneum and the subsequent loss of the mesothelium.

By definition, it is continuous with the tunica propria of two peritoneal surfaces.

It differs from the migration fasciathat results from the migration of primitivetissues during development in which migration produces linear orientation of

the connective tissue fibers, which, in turn, are compressed by further growth.

FIGURE 12-40. Ectopic adrenal in kidney. The ectopicadrenal tissue is usually subcapsular and is most often inthe upper pole. It may assume a plaque-like form (as inthis image) but can also be wedge-shaped or spherical.The gross appearance of this anomaly can raise concernfor neoplasia. (From MacLennan GT, Resnick MI, BostwickD: Pathology for Urologists. Philadelphia, Saunders, 2003.)

Ectopic adrenal cortical cellswithin renal parenchyma

FIGURE 12-41. Ectopic adrenal in kidney. Adrenalcortical tissue intermingles with normal renal tissue.The lack of circumscription imparts an infiltrativeappearance, and the histologic similarity between normaladrenal cortical tissue and clear cell carcinoma can creatediagnostic difficulty on intraoperative frozen sections.

Seminiferous tubules

Ectopic adrenal cortical tissuewithin testicular parenchyma

FIGURE 12-42. Ectopic adrenal tissue in testis. Nodulesof intratesticular ectopic adrenal tissue are usuallyless than 0.5 cm in size. The small aggregate of ectopicadrenal cortical cells shown here was an incidentalfinding in a testis excised for unrelated reasons.Diagnosis was confirmed by appropriate immunostains.


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because the bowel had rotated 180. In addition, the meso-duodenum fuses with a part of the primary retroperito-neum. Here, the result is fusion of two layers of mesentery(or four layers of peritoneal surface, each with its associatedinner stratum of connective tissue) with the primary retro-peritoneal surface and its layer of inner stratum.

This layer of fusion-fascia is superimposed over the inter-mediate stratum of retroperitoneal connective tissue thatwill form the renal (Gerotas) fascia, and thus covers mostof the kidney and ureter on each side.

By the seventh month of gestation, the layers of theintermediate stratum are well developed and form the renalfascia as the ventral layer splits into two layers, an anteriorlamina (Toldt) with the perirenal fat and a posterior lamina

(Zuckerkandl). The kidneys and related structures areenclosed between them. These lamina fuse laterally on eachside behind the ascending and the descending colon,where they form a single layer, the so-called lateroconalfascia (Fig. 12-43).

Thus, the peritoneum is associated with only one layer ofinner stratum of retroperitoneal connective tissue in all but twoareas: (1) where the mesenteries of the duodenum and ascend-ing and descending colon fuse to the primary retroperitoneum,and (2) as Denonvilliers fascia, in the retroprostatic pouch.

KIDNEY, URETER, AND ADRENALGLANDS: STRUCTURE AND FUNCTION

Retroperitoneal Fascias

Fascial Strata of the RetroperitonealConnective Tissue

The connective tissue between the body wall and the perito-neum can be separated into three layers: an inner stratum,just beneath the peritoneum associated with the intestinaltract and its vessels and nerves; an intermediate stratuminvest-ing the kidneys, adrenals, ureters, and their vessels andnerves; and an outer stratumcovering the epimysium of theparietal muscles (Table 12-6).

The conventions used in this book for naming the fasciallayers are shown in Table 12-7.

Multiple layers of fascia appear in areas of visceralmobility (mobility-fascia). For example, fascial layers areespecially numerous about the kidney as well as aboutthe pelvic and scrotal organs but are absent about theumbilicus.

Retroperitoneal Fascias and Spaces

The retroperitoneal fascias form the boundaries for theretroperitoneal spaces (Figure 12-43A).

Fascias

In the renal area, the fascias of surgical importance are therenal fascia and its extension, the lateroconal fascia, andthe fusion-fascia under the colon.

Renal Fascia

The renalor Gerotas fasciais derived from the intermedi-ate stratum of the retroperitoneal connective tissue, thestratum related to the urinary organs. The renal fascia hasan anterior and a posterior lamina, with the kidney andadjacent structures lying between in theperirenal space.

Anterior Lamina

The anterior laminaof the renal fascia (fascia of Toldt), alayer that includes the attached perirenal fat, is formed bylocal thickening of the intermediate stratum. Perirenal fatcan be distinguished by its paler color and finer texturecompared with that of the pararenal fat that lies outside therenal fascia. The perirenal fat contains connective tissuefibers that are especially concentrated about the upperrenal pole, and the fat is of greater thickness over the poste-rior and lateral surfaces of the fascia than over the anteriorsurface. It accumulates in larger quantities in men thanin women, and its bulk accounts for the more anteriorplacement of the colon in males compared with the lateral

DIFFERENTIATION OF MESENCHYME

T

ABLE

12-5

Primitive Late Fetal Adult

Subcutaneous layer Dermis Dermis

Superficial fascia Campers fascia, Scarpas fascia

Deep fascia Deep fascia

Body layer Muscles, ligaments, bones Muscles, ligaments, bones

Retroperitoneal layer Outer stratum Transversalis fascia

Intermediate stratum (urogenitalembedding)

Gerotas fascia

Inner stratum (intestinal embedding) Intestinal fascia


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A

B

FIGURE 12-43. A,Transverse-oblique view. B,Sagittal section.


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situation in females. The anterior lamina covers the ante-rior surface of thekidneyand adrenal gland.

The anterior lamina also becomes fused with the inner(intestinal) stratum at the sites where the vessels to thedigestive tract pass through from the aorta and vena cava.This stratum is difficult to illustrate as a separate layerbecause it is so closely related to the overlying primaryretroperitoneum.

Posterior Lamina

Theposterior laminaof the renal fascia (fascia of Zuckerkandl),also derived from the intermediate stratum, is thicker thanthe anterior one. Thepararenal fatlying dorsally is formedfrom it.

Over the psoas major and quadratus lumborum, theposterior lamina becomes fused with the fascia of the outerstratum, represented by the transversalis fascia. In the mid-line, the lamina is attached to the ventral surfaces of thevertebral bodies and to the anterior lamina of the renalfascia as the two laminas fuse and blend with the connectivetissue around the aorta, vena cava, and the renal artery and

veinas well as the tissue surrounding the autonomic nervesof the superior mesenteric plexus. Because the anteriorlamina also joins the dense connective tissue around the

great vessels, communication between the perirenal spaceson the two sides is virtually precluded.

Lateroconal Fascia

Laterally, behind the ascending and the descending colon,the anterior and posterior laminas of the renal fascia fuse tomake a single layer. The line of fusion is most commonlyfound directly lateral to the plane of the renal pelvis, butconsiderable variation is found. This single layer is calledthe lateroconal fasciaby radiologists from its appearance oncomputed tomography scans. It separates the anteriorfromtheposterior pararenal spaces(see Fig. 12-53).

The lateroconal fascial layer joins the properitonealfascia (from the inner stratum) at the white line of Toldt,closing the anterior pararenal space at its lateral margin.

Because the lateroconal fascia does not fuse with thetransversalis fascia but spreads anterolaterally around thebody wall between the transversalis fascia and the perito-neum, the posterior pararenal space continues forward asthe properitoneal space with its contained properitonealfat. It is this extension of fat that provides the radiologicallyvisualized flank stripe. More anteriorly, the lateroconalfascia ceases to be a distinct boundary between the two para-renal compartments; they become a single space.

FASCIAL LAYERS

T

ABLE

12-6

Layer Structure Function

PERITONEUMPrimary retroperitoneum Lining of body cavity

Secondary retroperitoneum (mesenteric)RETROPERITONEAL CONNECTIVE TISSUE LAYERSInner stratum Intestinal fascia, fusion-fascia Intestinal embedding

Intermed. stratum Renal fascia Urogenital embedding

Outer stratum Transversalis fascia (endopelvic fascia, lateralpelvic fascia, obturator fascia)

Lining of body wall

BODY WALL

Epimysium, muscles

CONVENTIONS FOR RETROPERITONEAL FASCIAL LAYERS

TABLE

12-7

Lamella Lumbodorsal fascia Posterior, middle, and anterior

Denonvilliers fascia Anterior and posterior

Lamina Renal (Gerotas) fascia Anterior and posterior

Stratum Retroperitoneal computedtomography

Inner, intermediate, and outer


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Colonic-Peritoneal Fusion-Fascia

With rotation of the colon and its mesentery, the perito-neum on each side of the colonic mesentery fuses with thesingle layer of the primary retroperitoneum behind them toform a single layer of fusion-fascia (see Figure 6-15). Themargin where this fusion-fascia meets the lateral parietal

peritoneum and the fused lamina of the renal fascia (latero-conal fascia) is marked by a linear thickening, the white lineof Toldt.

The single layer from the three-layered peritonealfusion-fascia may be separated from the underlying anteriorlamina of the renal fascia by blunt dissection, so that theascending or descending colon can readily be mobilizedmedially, leaving the kidney still covered by the anteriorlamina.

On the right side, the fused layer covers the ventralsurface of the caudal half of the right kidney, and its caudallimit depends on how much of the cecum is fixed to theprimary retroperitoneum. On the left, the caudal third ofthe kidney is beneath the fusion-fascia and the fixation endsat the sigmoid colon.

Spaces

Three clinically important spaces or compartments liebetween the fascial layers, which are revealed not only byanatomic dissection but also by roentgenography andcomputed tomography. These are (1) an anterior pararenalspace, (2) a perirenal space, and (3) aposterior pararenal space.

Anterior Pararenal Space

This compartment lies between the inner stratum, the layer

associated with the posterior parietal peritoneum, and theanterior laminaof the renal fascia. It is limited superiorly byadherence of the renal fascia to the inner stratum in thecolic gutters but is continuous laterally with the properito-neal compartment. Because of the folding of the mesocolonand the formation of layers of mesentery, radiologists, fromtheir studies on the diffusion of ascites and pancreatic fluid,have included the ascending and descending colonand theduodenum and pancreasand their mesenteries within theanterior pararenal space. However, on a developmentalbasis, this radiologic space is in the intermesenteric domain(see Figure 6-16 B). Thus, the anterior pararenal spaceproper lies behind the layers of fusion-fascia created by theposterior fixation of the colon to the primary peritoneum,and it lies over the anterior lamina of the renal fascia. It isactually a potential space; normally, it is empty. In surgery, itis important because it is the plane of this space that isfollowed medially from the white line of Toldt during mobi-lization of the colon to expose the kidney.

Perirenal Space

The perirenal compartment lies between the anterior andposterior lamina of the renal fascia and contains a kidney,adrenal gland, and ureter encased in fine areolar tissue andperirenal fat. The compartment is limited medially, laterally,and superiorly by fusion of its fascias.

Posterior Pararenal Space

This compartment separates the posterior lamina of therenal fascia from the transversalis fascia (of the outerstratum of the abdominal fascia). It is continuous with theproperitoneal space in the flank. This space contains coarsefatty-areolar tissue, the pararenal fat, derived as the poste-

rior layer of the renal fascia (intermediate stratum). It has ayellow-orange color compared with the light yellow color ofthe perirenal fat.

Medially, the posterior lamina of the renal fascia fuseswith the transversalis fascia to close the pararenal space overthe psoas major and quadratus lumborum, although the siteof junction and thus the extent of the posteromedial exten-sion of the pararenal space varies by as much as 10 cm. Theline of fusion encountered surgically is a dense band thatusually must be divided sharply.

The peritoneum over the transverse colonis continuouswith the parietal peritoneum made up of the fusion-fascia ofthe two layers of mesocolon and a single layer of primaryperitoneum (Fig. 12-43B).Under the peritoneum, the innerstratumof the retroperitoneal connective tissue overlies theanterior pararenal space. The anteriorand posterior lami-nasof the renal fasciaconfine thekidneyand ureterwithintheperirenal space.

Retroperitoneal Fascias and Spaces;Coronal View

For renal surgery, two layers of fascia are of concern. One isthe renal fascia, described earlier from a transverse-obliqueview and shown here from a coronal view (Fig. 12-44),andthe other is the transversalis fascia.

Renal Fascia

At the upper margin of the adrenal gland, fusion of theanterior and posterior laminas of the renal fascia tothe intrinsic fascia of the diaphragmcloses the cephaladend of the perirenal space. The seal is not completebecause perirenal gas has been observed to escape intothe mediastinum.

An incomplete fascial septum has been described sepa-rating the adrenal gland in a compartment above thekidney, but such a division has not always been described ondissection nor is it found at surgery or during perirenal gasinsufflation.

Because both laminas extend into the pelvis, one can pic-ture Gerotas fascia as a large, fairly sturdy but elastic bag. Itis known to be elastic because it will retain a large amount ofblood under pressure after renal injury. The bag is invertedover the kidneys and adrenal glands, with its front and backsides adherent to each other in the midline. Thus, hemor-rhage from the kidney may extend only in a caudal directionbecause it is restricted superiorly and medially by fascialfusion. Bleeding may be slowed or arrested by the limitingdistensibility of the anterior layer of the renal fascia.

In the pelvis, the posterior lamina of the renal fasciamerges with the transversalis fascia of the outer stratum.The anterior lamina continues caudally to enclose theureter in a sheath as far as the bladder region.


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Periureteral fibrosis involves only the intermediate stra-tum of retroperitoneal connective tissue within the renal

fascial laminas. The caudal margins of the two layers of therenal fascia are not firmly fused because gas instilled peri-rectally into the space fills the perirenal area. Similarly,barium suspension injected perirenally exits into the peri-vesical and perirectal areas.

Transversalis Fascia

The transversalis fascia, as well as those fascias of the pelviswith which it is continuous, are derivatives of the outer stra-tum of the retroperitoneal connective tissue. The transversa-lis fascia has been called the parietal fascia, analogous to theparietal peritoneum, to differentiate it from migration-fasciasand fusion-fascias and to indicate that it is the lining of theabdominal and pelvic cavities. It is a substantial layer of con-nective tissue intimately related to, but not part of, the epimy-sium of the underlying muscles. It is called the transversalisfascia because of its wide distribution beneath the transversusabdominis, but because this same stratum is distributed overall the muscles lining the abdomen and pelvis, the transversa-lis fascia must be considered part of an extended layer thatincludes the fascia of the pelvis. Thus, it is continuous withthe obturator and iliacus fascia, the fascia of the pelvic dia-phragm, the fascia of the femoral sheath and canal, and theinternal spermatic fascia. It may be fused with the intrinsicfascia (epimysium) of the psoas major. It is also continuouswith the so-called endopelvic fascia, although technically the

termendopelvic fasciamay be better reserved for that portion

of the transversalis fascia that forms collars around exitingorgans, such as the prostate in males (where it has been

called the lateral pelvic fascia), the urethra and vagina infemales, and around the lower rectum and anal canal.

Renal Envelope and Adjacent Body Wall

Fascias And Spaces

The fascial layers over the kidney are shown cut away(Fig. 12-45).From posterior to anterior, they are the psoasfascia, pararenal space, posterior lamina of rectal fascia,perirenal space, anterior laminaof the renal fascia, parare-nal space, and fusion-fascia (behind the ascending anddescending colon and peritoneum, not shown).

Diaphragm and Ligaments of the PosteriorBody Wall (see Fig. 8-10)

The diaphragm is attached to the vertebral column by theleft and right crus, between which the great vessels run.These crura are attached to the bodies of the upper twolumbar vertebrae and are joined anteriorly over the vesselsas the median arcuate ligament.

Lumbocostal archesor arcuate ligaments are formed from thetransversalis fascia. The medial arcuate ligamentsare bandlikethickenings of the fascia that extend from the tip of the trans-verse processes of the L1 vertebra across the psoas muscles toattach to the disk between the L1 and L2 vertebrae and to adja-

cent tendinous parts of the crura of the diaphragm. The lateral

FIGURE 12-44.


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arcuate ligaments are similar thickenings of the transversalisfascia that extend from the tip of the transverse processes of the

L1 vertebra across their respective quadratus lumborummus-cles to attach near the tips of the 12th ribs. They are the site oforigin of parts of the diaphragm and, in some areas, they limitthe upper border of the renal fascia.

Surgical Planes

The kidney may be approached without entering the renalfascia through two separate planes, one through the poste-rior and the other through the anterior pararenal space(Fig. 12-46).

FIGURE 12-45.

FIGURE 12-46.


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The posterior aspect of the kidney may be approachedthrough theposterior pararenal spaceby dissecting betweentheposterior laminaof the renal fasciaand the transversalisfascia, a dissection aided by the intervening pararenal fat layer.

Access to the anterior aspectof the kidney and its vessels isaccomplished by opening the anterior pararenal space bymedial mobilization of the fusion-fascia of the descending

or ascending mesocolon (including the parietal perito-neum) from the underlying anterior lamina of the renalfascia(see Fig. 12-45).starting at thewhite line of Toldt.

As the diaphragm is approached, the layers of the renaland transversalis fascias almost disappear, leaving the intrinsicfascia (epimysium) of the diaphragm against the peritoneum.

To avoid entering the peritoneum, dissection may beperformed beneath the diaphragmatic intrinsic fascia.

POSTERIOR BODY WALL

Anterior View

Removal of the transversalis fascia exposes the structures onthe internal surface of the posterior body wall and the greatvessels (Fig. 12-47).

Diaphragm

Three openings are found. Uppermost is the vena cavalaperture that opens through the diaphragm in the centraltendonat the junction of its right leafand central part. The

aperture accommodates thevena cavaand the right phrenicnerve. More central is the esophageal aperture that goesthough the muscle fibers of the right crus opposite the10th rib. The fascia of the diaphragm, continuous with thetransversalis fascia, encircles the diaphragmatic portion ofthe esophagus as a collar at its entrance into the abdomen,forming the phrenico-esophageal ligament. The most cau-

dal opening is the aortic aperture. The rightand left cruraof the diaphragm pass on either side of the 2nd and3rd lumbar vertebrae to provide this opening for the aorta.Here, the diaphragm lies anterior only to the aorta, which,in turn, lies against the vertebral bodies. The thoracic ductalso passes through this aperture, as well as the thoracicsplanchnic nerves that go to the celiac plexus.

The diaphragm is attached to the 1st lumbar vertebraby the medial arcuate ligamentand to the 12th rib by thelateral arcuate ligament.

Musculature

The quadratus lumborumemerges from beneath the lateralarcuate ligament to reach the lower border of 12th ribandthe transverse processes of the first four lumbar vertebrae.Caudally, it joins the iliolumbar ligament and the medialpart of the iliac crest. The iliacusis attached above to theinner surface of the iliumand sacrum, and ends below inthe tendon of the psoas major. Thepsoas majorpasses un-der the medial arcuate ligament to attach to the body of the12th thoracic vertebra and to the anterior surfaces of all thelumbar vertebrae. It terminates on the lesser trochanter of

FIGURE 12-47.


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Transverse Body Section, T12 Level,Viewed from Below

Right Side (R)

The upper pole of the right kidneyis surrounded by fat in theperirenal space contained within the anterior and posteriorlaminasof the renal fascia (Fig. 12-50).The adrenalis in the an-terior portion of the compartment. The transversalis fasciaandcrus of the diaphragm lie dorsally. The 11th intercostal arteryand nerverun beneath the 11th ribanterior to the intercostalmusculature. The right lobe of the liver, with the rightand mid-dle hepatic veins, is within theperitoneal cavityanterior to therenal fascia. The inferior vena cavais anterior to the right crus.

Left Side (L)

The section crosses the upper portion of the left kidneyandthe lower part of the left adrenal gland. The two laminasof the renal fasciaenclose them and continue laterally asthe lateroconal fascia. The posterior pararenal space liesdorsal to these fascias. The spleenand stomach, surroundedbyvisceral peritoneum, are suspended by the gastrosplenicligament. A portion of thepleural spaceis seen anterior tothe diaphragm. The thoracic aortalies behind the left crusof the diaphragmadjacent to the thoracic duct.

Transverse Body Section at the L1 Level

The renal arteries divide into segmental arteries as theyenter the renal hila (Fig. 12-51).The lowest part of the ad-renal glandis at this level on the right. At this level, neither

diaphragmatic cruscovers the front of the aorta. The celiacganglia lie anterior to the right and left crura of the dia-phragm to cover the anterior surface of the aorta. Theascending lumbar veinlies against the body of the L1 verte-bra. The epiploic foramenmarks the entrance to the lesser

sac, and separates it from theperitoneal cavity(greater sac).Theportal veinand common bile ductare anterior to theforamen. The splenic vein runs to the left.

Dorsal to the 12th riband the rightand left kidneysarethe iliocostalis muscleswith the adjacent longissimus.

Transverse Section at the L2 Level

The right ureter is anteromedial to the lower pole of thekidney. The right lobeof the livercovers the right kidney.

The left renal veinissues from the vena cava, and the leftrenal arterybranches from the aorta (Fig. 12-52).The leftgonadal veinlies lateral to a main branch of the renal vein.The portal vein is anterior to the vena cava. The splenic(left colonic) flexureis anterior to the renal fascia and in-tervenes between the spleenand the left kidney. The tail ofthepancreasoverlies the left kidney.

The quadratus lumborum forms a backing for the kid-ney, with the erector spinaeposteriorly and the latissimusdorsilaterally.

Transverse Section at the L2l3 Level

The jejunum lies anterior to the left kidney behind thebody of the pancreas. The ascending colon is anteriorto the right kidney behind the right lobe of the liver(Fig. 12-53).The uretersare placed in line with the lateral

FIGURE 12-49.


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The right kidney lies deep to the latissimus dorsi, theiliocostalispart of the erector spinae, the quadratus lumbo-rum, the 12th rib, and the psoas major (Fig. 12-54). Therenal hilumcontains branches of the renal artery and therenal vein.

The anterior and posterior lamina of the renal fasciaenclose theperirenal space,with thepararenal spaceposte-rior over the transversalis fascia.

Sagittal Section Through theRight Adrenal

The right adrenallies at a level between the 11th and 12th ribsbelow the caudate lobe of the liverand is adjacent to the infe-rior vena cava(Fig. 12-55).The superior and descending por-tions of the duodenum lie slightly inferiorly. The right renalarterycrosses in theperirenal space.

FIGURE 12-52.

FIGURE 12-53.


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Sagittal Section Through the Left Kidney

The body of the pancreas and the splenic vein andarterylie anterior to the upper pole of the left kidney,with the spleensituated superiorly and the body of thestomachanteriorly (Fig. 12-56).The short gastric arter-ies are found between the spleen and pancreas. The

greater omentum joins the stomach to the transversecolon, which in turn is supported by the transversemesocolon. The descending colon is anterior to thelower renal pole. The branches of the renal artery andthe renal vein are in the hilum, and the ureter lies justoutside. The quadratus lumborumand iliocostalisover-lie the kidney dorsally.

FIGURE 12-54.

FIGURE 12-55.


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Coronal Section Through the Renal Hila

On the right side, the right kidneyis opposite the L2and L3vertebrae,next to thepsoas major,encased in theperineph-ric space (Fig. 12-57).The right adrenal gland is superior,

adjacent to the lumbar portion of the diaphragm.On the left side, the left kidney is opposite L1and L2,

with the head of the pancreasand splenic arteryand veinabove. The left adrenal glandis over the upper pole. Thesplenic flexurelies lateral to the kidney.

RENAL STRUCTURE

Developmentally and anatomically, the kidney may bedivided into two parts: secreting and conducting. The secre-tory structures are the glomeruli, proximal convoluted tu-bules, loops of Henle, and distal convoluted tubules. Theconducting structures are the collecting tubules, the minorand major calices, and the pelvis.

Gross Structure

The kidneys tend to be of the same dimensions and generalconfiguration, the size depending on that of the individual.The exception is that in newborns, the size of the kidneyrelative to body weight may be as much as three times thatof the adult. The kidney of the adult male is about 12 cm inlength, 6 cm in width, and 4 cm in thickness and weighsabout 150 g; that of the female is slightly smaller, with aweight of around 135 g.

Lateral Aspect

The anterior surface of the kidney is rounded, whereas theposterior surface is flatter (Figs. 12-58Aand 12-59).

The depressions or lobulations seen on the surface of

the kidney in young children are reflections of the interlo-bar septaor renal columns of Bertin that mark the divisionsbetween the lobes. Before the age of 4 years, these groovesare prominent, but with the thickening of the peripheralcortex, they disappear. Their persistence indicates a differ-ent arterial arrangement, the arteries dividing extrarenallyinstead of in the hilum.

A deeper, longitudinal groove(the white line of Brdel)is seen anterior to the plane of the greater curvature.It marks the major division between the anterior and poste-rior row of pyramids and the corresponding rows of calices.Because the arteries do not follow the pattern of the calices,this depression is not an indication of the so-called avascularplane. In fact, major arteries to the anterior portion of thecortex cross this line.

Coronal Section

An opening in the concave border of the kidney, therenal hilum, admits the renal pelvis, renal artery andvein, lymphatics, and nerves into the renal sinus(Figs. 12-58Band 12-60).The sinus contains fatty tissuethat is continuous with the perirenal fat. Although ear-lier anatomists believed the sinus to be closed at thehilum, observations on peripelvic extravasation show itto be open.

FIGURE 12-56.


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The kidney is enclosed in a fibrous capsulethat is readilyseparable from its surface, unless it has been involved ininflammation.

The tensile strength of the capsule is not great but isusually enough to hold mattress sutures, especially if bol-sters are used. It has enough substance to be felt as resis-tance to a trocar entering for percutaneous nephrostomy.

The renal pelvis is joined by both major and minorcalicesinto which the terminations of each renal pyramidintrudes as apapilla.

Calyces and their Parts

The conducting structures, ureter, pelvis and calyces, are acontinuous entity, as one would expect from their embry-onic origin as branches from the wolffian duct. They havesimilar coats and the smooth muscle in each has a helicalarrangement as in the ureter, although the musculature ofthe ureter is thicker.

From a lobe, the collecting ductsin apyramidempty intoa calyxthrough apapilla.They open through a cribriform

FIGURE 12-57.

A B

FIGURE 12-58.


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platethat is ringed by a fornix.A minor calyxdrains a single,compound or conjoined papilla; a major calyxdrains two ormore minor calyces (Figs. 12-61Aand 12-61B).

A papillamay be single and drain one pyramid of thekidney (simple papilla). Two or more papillae may fuse andcome to lie together as a single entity. With the fusion, themedial margins of the calyceal cups lose their individualidentity, resulting in a compound papillathat empties into acompound calyceal cup.With lesser degrees of pyramidal

fusion, both papillae retain partial identity as conjoinedpapillae and drain into two calyceal cups that also retaintheir identities but do not develop separate necks. Theresult is conjoined papilla with a conjoined or compositecalyceal cup.

The term calyx is applied to the combination of threeelements: (1) a cup-shaped receptacle, (2) a connecting

neck, and (3) a funneled tube that opens into the renalpelvis. The word calyxis also applied to the isolated cup andneck. Strictly, calyx means cup, so the word is appropriatefor that cup-shaped portion into which the papilla pro-trudes. Because calyx is also the word used for the entirecomplex through such usage as minor calyxand major calyx,confusion arises when attempting to refer to the subdivi-sions of the complex. Despite the disadvantages of addinganother term, for clarity the word calyceal cupreplaces thestrict meaning of calyxin this text. The term infundibulumisdefined anatomically. The word calyxthen means the com-bined system of cup, neck, and infundibulum (Figs 12-61C,D, E and 12-62).

The calyceal cupis the hemispherical portion of the calyxthat is indented to accommodate the papilla. The proximalportion of the cup has a conical taper that connects the cupwith the more proximal narrow part of the system, which isnamed the calyceal neck(Fig 12-61C).In a minor calyx, theneck provides the transition from the taper of the cup to theexpanse of the renal pelvis. In a major calyx, the neck isthe connection of the cup to the wider lumen of the next seg-ment, the calyceal infundibulum. The infundibulum inter-venes between the necks (and cups) of two or more papillaebefore connecting to the pelvis. The term is appropriatebecause the structure resembles and functions as a funnel,collecting from the necks and emptying at the infundibulopel-vic junction.Thus, by definition, a minor calyx has one neck

and one cup; a major calyx has at least two necks and two ormore cups joined to the pelvis by an infundibulum.

To summarize, a minor calyx is a combination of calycealcupand calyceal neck. A major calyxdrains two or more calycealcupsand accompanying calyceal necksthrough a calyceal infun-dibuluminto the renal pelvis.

The pelviscan be considered a dilated portion of theureter, with the calycesas its branches.

The pelvis divides primarily into two or three major caly-ces, defined as those with an infundibulum and two or morenecks and cups (Fig. 12-61D). Secondary division of themajor calyces results in seven or eight nonbranching minorcalyces. In the typical kidney, these are arranged in twolongitudinal rows, with the calyceal necks of those in theposterior row being more attenuated than the stubbieranterior ones. The ends of the kidneys are drained by upperand lower pole calyces that are frequently compound orconjoined.

Two types of pelves are recognized: The common onehas a funnel shape that remains open to receive urine priorto ureteral peristalsis; the other has a more rounded shapewith an apparently closed outlet, the box pelvis. From asurgical viewpoint, the pelvis is considered intrarenal orextrarenal depending on its relation with the hilum, andintermediate variations are possible. An intrarenal pelvismay be viewed as the result of later division of the uretericbud, resulting in shorter calyces than in the extrarenal type.

Renalpelvis

Renalvein

Renalartery

Aorta

Ureter

FIGURE 12-59. Normal kidney, showing gross structuresbefore sectioning.

Papilla Renal sinus

Renal hilum Septum ofBertin

PyramidPeripheral

cortex

FIGURE 12-60. Normal kidney, coronal section through

the center.


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Such a pelvis makes surgical access to and manipulationwithin the interior of the kidney more difficult. The capac-ity of the pelvis is about 6 ml; volumes higher than 15 mlmay be considered abnormal.

The major calyces may develop from a single pelvis (truepelvis of Brdel), from a transitional form, or from adivided pelvis with a zone of cortical substance between thesecond and third, and the fourth and fifth complete calyces.

The divided pelvis, the extreme of which is the bifidpelvis shown in the figure, has a smaller upper pole majorcalyxand a larger lower pole major calyx, leaving the mid-portion of the kidney without branches (Fig. 12-61E).In thedivided kidney, the arrangement of the minor calycesseldom follows the usual anteroposterior pattern, thus pos-ing problems for calyceal puncture and requiring obliqueradiographs.

Radiologic Orientation

The kidneys usually extend from the level of the T12 to L3vertebrae, being slightly lower in females. The right kidneylies 1 to 2 cm lower than the left. The kidneys are slightlyrotated on a vertical axis in three planes: coronal, trans-verse, and sagittal.

A B

C

D E

FIGURE 12-61.

Majorcalyx Infundibulum

Pelvis

Minor calyx

FIGURE 12-62. Normal kidney, coronal section, showingfeatures of the upper collecting system. (Image courtesy ofPedro Ciarlini, MD.)


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Coronal Projection

The upper pole is more medial than the lower by an angleof 13 (Fig. 12-63A).

Transverse Projection

The pelvis and hilum have a more anterior position thanthe outer convex border by an angle of 30 (Fig. 12-63B).

Sagittal Projection

The long axis of the kidney is angled posteriorly by about10 (Fig. 12-63C).

Radiologic Orientation for Endourology,Right Kidney

In transverse section, the body is shown placed in theoblique position preparatory to puncture of a posteriorcalyx.

It is necessary to know the angles that the calyces takerelative to the coronal plane of the body prior to percutane-ous puncture (Fig. 12-64). The use of lateral and obliqueradiographic views in addition to an anteroposterior viewallows mental construction in three dimensions. Computedtomographic reconstruction of pyelograms produces athree-dimensional image that can be useful.

The orientation of the calyces is variable. At the poles,the angles taken by the necks of the compound or conjoinedcalyces are not constant, but those in the midportion of thekidney are aligned in two rows anteriorly and posteriorly atan angle of about 70 to each other (right, 60 1676;left, 63).

Measurement from the Coronal Plane of the Body

For the right kidney, the angle of the axisof the anteriorcalyces, measured anteriorly from the coronal plane of thebody, averages 16. The angle of theposterior calycesaver-ages 60 posterior to the coronal plane.

Measurement from the Frontal Plane of the Kidney

From the frontal plane of the kidney, the angles are 46anteriorly for the axisof the anterior calycesand 30 poste-riorly for that of theposterior calyces.

Radiologic Orientation for Endourology,Left Kidney

Orientation from the Coronal Plane of the Body

The angle of the axis of the anterior calyceal angle is3 anterior to the coronal plane of the body. The typicalanterior set of calyces lies close to the coronal plane. There-fore, most portions of an anterior calyx are visualized on aurogram of a supine subject, whereas the posterior calycesappear end-on. The angle of the axisof theposterior calyxis 60 degrees posteriorly from the coronal plane (Fig. 12-65).

Orientation from the Frontal Plane of the Kidney

From the frontal plane of the kidney, the anterior calyceshave an angle of 33 anteriorly; theposterior calyceshave asimilar angle of 30, but posteriorly. However, there is greatvariation in calyceal morphology and arrangement.

For an estimation of renal mass, measurement fromthe papillary tip of an anterior calyx to the surface is fairly

A

B

C

FIGURE 12-63.


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reliable if it is combined with measurement of overallrenal length.

INTRARENAL STRUCTURES

Fornix and Papilla

The papilla of the renal pyramid invaginates into thecalyceal cupof a minor calyx (Fig. 12-66).The fornixmarksthe site where the wall of a calyceal cup joins the renal pa-renchyma; it appears as a rim around the base of the papilla.The fornix is marked at the margin of the papilla by achange from the thick, whitish epithelial wall of the

kidneys, ureter and adrenal gland.pdf

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