sample chapter differential diagnosis in obstetric and gynaecologic ultrasound 3e by bisset to order...

P A R T I Obstetrics

Early Pregnancy, 02

Fetal Well-Being and Growth, 24

Structural Fetal Abnormalities, 78

Fetal Face and Neck, 119

Fetal Thorax, 140

Fetal Echocardiography, 150

Fetal Abdomen and Pelvis, 169

Fetal Genitourinary System, 200

Fetal Musculoskeletal System, 220

2

C H A P T E R

1 Early Pregnancy

MENSTRUAL AGE VERSUS GESTATIONAL AGE Menstrual age refers to the fi rst day of the last normal menstrual period preceding pregnancy. The menstrual age is used clinically for dating pregnancy as it is an easily identifi able landmark. Gestational age refers to age from conception and usually lags behind the menstrual age by 2 weeks.

THE FIRST TRIMESTER The fi rst trimester is defi ned as the 13 weeks fol-lowing the fi rst day of the last menstrual period. The fi rst clue that the patient might be pregnant is the appearance of a small cyst eccentrically located within a single layer of the endome-trium; this is soon followed by the appearance of a double bleb sign, the yolk and then an echo-genic cylinder that is the embryonic pole. There is an echogenic rim around the early GS that is the decidual reaction. The amniotic membrane is seen to surround the early embryo; the YS is out-side the amniotic cavity and is gradually pushed to the periphery as the amniotic cavity expands. These early fi ndings are depicted in Figure 1-1 .

ROLE OF ULTRASOUND IN THE FIRST TRIMESTER 1 • To identify site(s) of pregnancy, e.g. intrauterine,

interstitial or ectopic • To detect early pregnancy failure

1 US should not be used solely as a diagnostic test to confi rm the presence of uncomplicated pregnancy.

• To predict outcome in the presence of a live embryo

• To assess gestational age, uncertain dates or LMP discrepancy

• To determine the number of embryos and assess chorionicity and amnionicity

• To evaluate retained products of conception • To diagnose gestational trophoblastic disease • To diagnose some fetal anomalies With TVS, there is improved detection rate of fetal anomaly in the fi rst trimester. However, caution is needed in interpreting certain fi ndings in the fi rst trimester such as cystic hygroma, choroid plexus cysts, pyelactasis and echogenic bowel, which may resolve spontaneously. A signifi cant false-negative rate for fetal anomaly has also been recorded in the fi rst trimester of pregnancy. • To assess associated maternal abnormalities,

e.g. ovarian cysts, uterine leiomyomas and retained IUCD

• US-guided chorionic villus sampling • To assess therapeutic abortion

PREDICTORS OF EARLY PREGNANCY FAILURE Pregnancy failure in the fi rst trimester is a com-mon problem, as approximately a quarter of pregnancies fail during this period.

Lack of Cardiac Activity

Absent cardiac activity is taken to indicate death but it should be remembered that in very small

A B

C D

E F

G H FIGURE 1-1 Ultrasound features of early pregnancy. The earliest evidence of an IUP is the appearance of the GS, seen as a small cyst in a single layer of the endometrium ( A ); soon a tiny two-compartment bleb appears inside ( B ); this is the double bleb sign. Occasionally, a small amount of fl uid might be seen outside the GS; this early bleed might not be signifi cant but does warrant a follow-up for confi rming viability ( C ). By about 5 – 6 weeks, a small well-defi ned internal cyst, the YS, and a tiny bar of tissue, the embryonic pole, appear in the GS ( D ); at this time, embryonic cardiac fl icker might also become apparent. An early sign of healthy pregnancy is the echogenic rim that is the decidualized endometrium ( E ); the absence of this echogenic rim should raise concern of an abnormal pregnancy ( F , a blighted ovum). The YS, vitelline duct and amni-otic membranes become evident as well as a recognizable embryo with a large head and small limb buds ( G , H ); the YS is outside the amniotic membrane and as the amniotic cavity forms and expands, this is pushed by the amnion against the chorion; this is seen very well in image H . (Image H, courtesy of Dr Allen G. Worral, USA.)

CHAPTER 1 Early Pregnancy4

embryos (<4 mm) cardiac fl icker might not be appreciated and ultrasound should be repeated after a few (2 – 3) days to confi rm this impression. An embryonic length of 5 mm is a threshold value in ultrasound at which cardiac activity should be visible in all cases ( Figure 1-2 J, O – Q).

Yolk Sac Characteristics

The YS functions as a haematopoietic organ and facilitates nutrition transfer in early pregnancy gestation. An abnormal Yolk Sac is associated with embryonic death and poor pregnancy out-come. Absence of a YS on TVS when GS size is 8 mm or more is said to be 100% sensitive for anembryonic gestation but has a 9% specifi city and a positive predictive value of 65%. Out of these, 22% subsequently develop a viable preg-nancy. However, the presence or absence of a YS cannot be used to determine if a pregnancy is normal when the GS is smaller than 18 mm. Cal-cifi cation is associated with a poor prognosis. An abnormally shaped YS and lack of growth of the YS are further signs of pregnancy failure. Unusu-ally large or small YS ( Figure 1-2 C – F) has been associated with embryonic death. Nevertheless, transient abnormalities of YS shape may some-times occur in normal pregnancies.

Gestational Sac Features

Just like embryonic length threshold values, there are values for other structures that help in deciding whether to wait or diagnose abnor-mality. On TVS, an MSD of ≥ 18 mm should always have a visible YS, and a mean sac diam-eter of >20 mm should always have a visible embryo. If the sac diameter has not reached the threshold value, it would be prudent to wait a few days; if the sac diameter exceeds threshold values without the associated fi nd-ings, an abnormal pregnancy can be diagnosed ( Figure 1-2 A and B).

An irregular GS, thin or absent echogenic endo-metrium (<2 mm) around it (decidual reaction), absent double decidual line sign are portends of poor outcome.

Small Sac Size: Discordance between MSD and CRL

There is a large range of normal GS size. The peak average difference between MSD and CRL is 14.4 mm at 8 week menstrual age, which progressively diminishes to less than 1 mm by 12 weeks menstrual age. Close follow-up is nec-essary with borderline fi ndings as patients can go on to develop a normal pregnancy.

Abnormal Amnion

A collapsing amnion, an amnion with irregular margins and an amnion with no visible embryo indicate pregnancy failure. An enlarged amni-otic cavity or a YS diameter more than 2 standard deviations above the mean when compared with mean GS diameter is associ-ated with poor outcome. A small amniotic cav-ity with early oligohydramnios is a worrying sign but should be diagnosed only when the threshold of MSD-CRL <4 mm is crossed ( Fig-ure 1-2 L and M).

FIRST TRIMESTER ANATOMY THAT MAY MIMIC FETAL ANOMALY

Fetal Rhombencephalon

The rhomboid fossa of the normally developing rhombencephalon can appear as a small (3 – 4 mm) ‘cystic’ structure in the posterior aspect of the cranium, between 8 and 10 weeks menstrual age ( Figure 1-3 C). It should not be confused with Dandy-Walker malformation, a cystic posterior fossa abnormality. See image: Fig 3-15, page 112.

Telencephalic and Mesencephalic Vesicles

The brain develops from the cranial part of the neural tube. During the fourth week, the fore-brain (prosencephalon), midbrain (mesencepha-lon) and the hindbrain (rhombencephalon) form as primary vesicles. During the fi fth week, the forebrain divides into the telencephalon and

5CHAPTER 1 Early Pregnancy

A B

C D

E F FIGURE 1-2 Ultrasound features in early failed pregnancy. ( A , B ) A large GS (18 – 20 m) without YS or embryonic pole and a poor echogenic rim is a feature of early anembryonic pregnancy (blighted ovum). An abnormally large YS (>7 mm) is often associated with an abnormal outcome and in both cases ( C , D ) pregnancy failed to progress. Small echogenic YSs ( E , F , arrows ) are also associated with poor outcome in many cases but a close follow-up in all cases of abnormal YS size is recommended because a few can go on to normal pregnancy.

Continued


G H

I

K

J

FIGURE 1-2, cont’d Subchorionic haemorrhage, white arrow, ( G – I ) can range from an extensive collection almost all around the GS ( G ) to a collection at one end ( I ); if the collection surrounds more than half the diameter of the sac or extends behind the placental implantation site the prognosis is worse but follow-up should be done as the outcome is unpredictable and many early pregnancies with early ominous looking collections go on to progress and many pregnancies with relatively trivial collec-tions fail to thrive. Cardiac fl icker should be visible from very early on and in this 8 weeks pregnancy ( J ) with recent slight bleed-ing it was not demonstrable; this is a black and white rendition of a Doppler image showing lack of cardiac activity and fl ow. This was a case of missed abortion. The patient in image ( K ) had a history of recent bleeding and on ultrasound a distorted compressed GS was noted low down in the region of the body; this was an abortion in progress and the sac was expelled within the next few hours, with no sac visible on a follow-up ultrasound after 24 h.


L M

N O

P Q FIGURE 1-2, cont’d First trimester oligohydramnios, diagnosed when the sac is tight around the embryo has a generally poor prognosis but caution must be used when diagnosing this. In some normal pregnancies ( L ) the MSD-CRL value falls below 10 mm. The threshold for diagnosing fi rst trimester oligohydramnios is ≤ 4 mm; image M shows a 12-week fetus with a large abdominal cyst and complete anhydramnios with no measurable pocket amniotic fl uid seen. ( N ) Eight weeks missed abortion with oligohydramnios. ( O ) Relatively normal looking embryo with absent cardiac activity; there is a large extra-amniotic space (arrow). ( P , Q ) Distorted featureless embryo with absent cardiac activity and a large sac. (Image N, courtesy of Dr Jaydeep Gandhi, India; image Q, courtesy of Dr Gunjan Puri, India.)


diencephalon and the hindbrain divides partially into the metencephalon and myelencephalon. The telencephalic and mesencephalic vesicles appear at about 7 weeks gestation and can be detected prenatally.

Physiologic Gut Herniation

This appears at about 8 weeks and may persist until 12 weeks in 20% of normal fetuses. The umbilical cord may be the site of cysts, varying from 2 to 7 mm, in under 1% of normal pregnan-cies ( Figure 1-3 A).

TRANSIENT FIRST TRIMESTER FETAL ANOMALIES With TVS, there is improved detection rate of fetal anomalies in the fi rst trimester. Caution is needed in interpreting certain fi ndings ( vide infra ).

Increased Nuchal Translucency

Increased fi rst trimester nuchal oedema/translu-cency (NT) may be a transient phenomenon. How-ever, persisting nuchal oedema may need close follow-up as it is an important ultrasonographic

A

B C FIGURE 1-3 Normal fi rst trimester structures that can mimic fetal anomalies. ( A ) Physiological gut herniation (white arrow); this is seen as an echogenic nodule projecting out of the abdominal wall, longitudinal section on the right and transverse section on the left. ( B ) Limb buds (open arrows) that can appear as small echogenic nodules on the ventral surface of the body. ( C ) Rhombencephalon appearing as a prominent cyst in the fetal brain (dashed arrow).


marker of fetal chromosomal abnormality. NT in the fi rst trimester is associated with aneuploidy particularly trisomy 13, 18 and 21. An increased NT at 11 – 14 weeks gestational age is a common fi nding in Down syndrome. NT is normally less than 2.5 mm; an increased measurement greater than 2.5 mm may indicate the presence of Down syndrome or other chromosomal anomaly ( Figure 1-4 A – E). The presence of normal karyotype in the presence of increased NT is a strong indication for detailed ultrasound examination for nonkaryo-type defects such as Noonan syndrome, Joubert syndrome and congenital heart defects. The pres-ence of an isolated increased NT is associated with 12.5% prevalence of chromosomal aberrations.

Very detailed protocols are available on how to acquire accurate and reproducible NT mea-surement ( Box 1-1 ).

Nuchal Cystic Hygroma

One review of 72 fetuses with cystic hygroma diag-nosed at 10 – 14 weeks gestation found the mean size of 7.9 mm. Just over half had chromosomal abnormalities of which the majority had Down syndrome. The outcome of pregnancy is usually unfavourable (miscarriage, elective termination, and serious structural abnormalities). The overall prognosis of fetal cystic hygroma ( Figure 1-4 F) detected during the fi rst trimester is poor, and thus sonographic evaluation of fetal nuchal translu-cency thickness in the fi rst trimester is crucial.

Axillary Cystic Hygroma

Sonographic diagnosis of fetal axillary cystic hygroma has been reported rarely, usually late in gestation. Axillary hygromas are usually small, transient, nonloculated cysts. Some are associ-ated with chromosomal abnormalities. An asso-ciation has been reported with trisomy 21 and 18. Early fetal axillary cystic hygromas are usu-ally different from postnatal axillary cysts in terms of prevalence, structure, and appearance. It also may be a normal variant in the develop-ment of the fetal lymphatic system.

Choroid Plexus Cysts

This is found in 3.6% normal fetuses; investiga-tors are divided on the question of amniocentesis in isolated CPC but most agree that the presence of additional US abnormalities is an indication for amniocentesis. Abnormal karyotype is found in 1 – 2.4% of fetuses with isolated CPC.

Hydronephrosis

Isolated mild pyelactasis (<3/4 mm) without progressive change is not associated with sig-nifi cant pathology and is found in 3.2% of fetuses. Mild pyelactasis is characterized by a small amount of fl uid in the renal pelvis and is affected by maternal hydration. However, mild pyelactasis may be a sign of early pathological state. The appropriate threshold for initiating further investigation particularly in the fi rst trimester is controversial but a close watch is essential.

Pericardial Effusion

Generally when a fetal pericardial effusion is observed it is along one portion of the ventricle or near an atrioventricular valve, but does not surround the heart. A pericardial effusion sur-rounding the heart is considered abnormal even when small.

Pleural Effusion

Pleural effusion is considered abnormal at any gestational age and even when transient the fetus needs to be evaluated for chromosomal abnor-mality, Turner syndrome, immune hydrops feta-lis, cardiac abnormalities, diaphragmatic hernia, lymphangiectasia and intrauterine infections. Sonographic appearances are those of anechoic fl uid collection that conform to fetal chest associ-ated with fl attening/inversion of the diaphragm and bulging of the thoracic wall. Chylous effu-sions are indistinguishable from serous pleural effusion in the fetus.


C D

E F

BBBAA

FIGURE 1-4 Nuchal translucency; normal measurement ( A , B ), increased NT ( C , D ), markedly increased ( E ); in this patient, the oedema is generalized and is all around the body (space suit appearance). There is posterior cystic hygroma forma-tion in ( F ); this has a very high association with aneuploidy, especially Turner syndrome. (Images B, D, and E, courtesy of Dr Allan J. Worral, USA; image F, courtesy of Dr Latha Nataranjan, India.)


Echogenic Bowel

Fetal echogenic bowel should be investigated and followed up carefully as it is considered as one of the soft markers for aneuploidy, IUGR, infec-tions and cystic fi brosis.

INTRAUTERINE FLUID COLLECTIONS THAT MAY MIMIC A GS A variety of conditions causing fl uid collections within the uterine cavity may, in the appropri-ate clinical setting, mimic a GS. Intrauterine fl uid collections lack the double ring margin of an IUP and in many of the causes listed below will lack a trophoblastic reaction. • Endometrial bleeding • Retained products of conception

• Incomplete abortion • Pseudogestational sac of EP • Endometrial carcinoma • Cervical stenosis/cervical obstruction due to a

carcinoma or previous surgery • Endometritis • Endometrial arterial aneurysm – this life-

threatening condition has been reported only once; on close inspection it was found to be pulsatile on US, while a duplex arterial wave-form was detected .

EMPTY GS A GS is classifi ed as empty when no fetal parts are identifi ed on abdominal scanning in a sac that exceeds 30 mm in diameter or with no YS in a sac that exceeds 20 mm in diameter. Most

• The gestational period must be 11 – 13 weeks and 6 days. • The fetal CRL should be between 45 and 84 mm. • The magnifi cation of the image should be such that the

fetal head and thorax occupy the whole screen. • A mid-sagittal view of the face should be obtained. This is

defi ned by the presence of the echogenic tip of the nose and rectangular shape of the palate anteriorly, the translu-cent diencephalon in the centre and the nuchal membrane posteriorly. Minor deviations from the exact midline plane would cause nonvisualization of the tip of the nose and visibility of the zygomatic process of the maxilla.

• The fetus should be in a neutral position, with the head in line with the spine. When the fetal neck is hyperex-tended the measurement can be falsely increased and when the neck is fl exed, the measurement can be falsely decreased.

• Care must be taken to distinguish between fetal skin and amnion.

• The widest part of the translucency must always be measured.

• Measurements should be taken with the inner border of the horizontal line of the callipers placed on the line that defi nes the nuchal translucency thickness – the crossbar of the calliper should be such that it is hardly visible as it merges with the white line of the border, not in the nuchal fl uid.

• In magnifying the image (pre- or postfreeze zoom), it is important to turn the gain down. This avoids the mistake of placing the calliper on the fuzzy edge of the line which causes an underestimate of the nuchal measurement.

• During the scan more than one measurement must be taken and the maximum one that meets all the above criteria should be recorded in the database.

• A new approach for the measurement of NT which improves the accuracy of measurements, is with the use of a semiautomated technique. The operator places a box in the nuchal area and the machine automatically selects the best measurement, which uses an algorithm that draws a line through the centre of the nuchal mem-brane and another line at the edge of the soft tissue overlying the cervical spine. The measurement obtained by this method is similar to that obtained manually and it is therefore applicable to the software of the Fetal Medicine Foundation.

• The umbilical cord may be round the fetal neck in about 5% of cases and this fi nding may produce a falsely increased NT. In such cases, the measurements of NT above and below the cord are different and, in the calcu-lation of risk, it is more appropriate to use the average of the two measurements.

BOX 1-1 Protocol for Measurement of Nuchal Translucency

Reproduced with permission from Fetal Medicine Foundation. Available at www . fetalmedicine . com .


empty sacs are abnormal in shape ( Figures 1-1F and 1-2A and B ).

Normal IUP 5 – 7 weeks

menstrual age

This is less likely with TVS as GS is seen as early as 32 days and is seen in all pregnancies with hCG levels of 1000 m IU/mL

Blighted ovum This term applies to arrested development of a fertilized ovum. Most blighted ova are of an abnormal karyotype

Pseudogestational sac of EP

The double decidual sign is absent in a pseudogesta-tional sac

POSITIVE β hCG WITHOUT IUP Human chorionic gonadotropin (hCG) is a glyco-protein hormone produced by trophoblastic tissues. As trophoblastic tissue is an essential part of preg-nancy; identifi cation of hCG is frequently sought to confi rm the presence of pregnancy. However, a false-positive hCG assay may arise in conditions other than pregnancy as hCG may be elaborated by the pituitary, exogenous sources, and both tro-phoblastic and nontrophoblastic neoplasia, result-ing in false-positive laboratory assays for hCG.

• Early IUP <5 weeks gestation • Recent complete or incomplete abortion • EP • β hCG-producing ovarian tumour – germ cell

tumour, primary ovarian choriocarcinoma • Theca lutein cyst associated with pharmaco-

logical stimulation with β hCG • Exogenous administration of hCG: hCG is

used by some as an aid in weight loss by intra-muscular or oral administration. Following cessation of hCG therapy for 24 h the hCG assay usually turns negative on a repeat assay.

• Pituitary hCG: Stimulated by gonadotropin-releasing hormone; suppressed by gonadotro-pin-releasing hormone agonist and oestrogen/progestin therapy. Can also be detected in postmenopausal women due to increased GnRH secretion .

• Trophoblastic neoplasm: Consists of pregnancy, gestational trophoblastic neoplasia, and pla-cental site trophoblastic tumours.

ULTRASOUND FEATURES OF EARLY IUP

Gestation Sac

A GS is surrounded by an echogenic asymmet-rical ring that should be visible at 5 weeks MA on transabdominal US scan, while on TVS a GS is seen at 32 days. A normal sac growth is 0.7 – 1.75 mm/day (mean = 1.33) from 5 to 11 weeks. In patients with early pregnancy with a question-able GS a 10 MHz intravaginal probe improves the diagnostic confi dence.

Double Decidual Sac

A DDS is useful at 4 – 6 weeks gestational age; it consists of two concentric rings of tissue sur-rounding a portion of an intrauterine GS. The sign develops as a result of protrusion of the GS into the uterus.

Yolk Sac

At 6 weeks MA, a YS and amnion should be visible on transabdominal US. On TVS, a YS is seen in every pregnancy between 36 and 40 days; the GS is between 6 and 9 mm. YS is seen in 100% normal pregnancies with β hCG level of 7200 m IU/mL.

Intradecidual Sign

This is when the GS is not suffi ciently large to impress, protrude into or deform the uterine cen-tral echo complex yet is completely embedded within the decidua. This sign precedes the double decidual sign. This sign does not appear to be sensitive or specifi c in the diagnosis of IUP.

Embryo with Heartbeat

Embryo with a heartbeat is expected in all preg-nancies >40 days and a GS >9 mm on TVS.


RISK GROUPS FOR EP EP rates have increased steadily from 4.5 per 1000 pregnancies in 1970 to 16.8 per 1000 preg-nancies in 1987. All women of reproductive age are at risk of EP.

Higher Risk Groups: EP

• Delayed transit of zygote �� Previous tubal pregnancy (10-fold increase) �� Previous tubal surgery �� Previous salpingitis particularly chlamydia �� Infertility – shared tubal abnormalities with

EP • Infertility �� Ovulation induction �� In vitro Fertilization multiple pregnancy

contributory factor �� Gamete intrafollicular transfer – contributory

factors include the hydrostatic forces gener-ated during transfer

�� Intrauterine contraceptive devices �� History of PID �� Increasing maternal age and parity

ULTRASOUND FINDINGS IN EP EP is not always easy to diagnose; the classic triad of missed period, pain and abnormal vaginal bleeding is frequently absent and adnexal mass or cervical tenderness cannot be demonstrated in many patients.

Correlation with ultrasound and serum β hCG help in making the correct diagnosis in many patients.

Ultrasound is fairly conclusive in the follow-ing situations. • The demonstration of a live pregnancy out-

side the uterus. With cardiac fl icker and/or the conclusive demonstration of a YS.

• The demonstration of a thick ring-like struc-ture with an echogenic rim and an extra-ovarian location is fairly specifi c. Beware of the corpus luteum that can mimic an ectopic, but the corpus luteum is ovarian

in location while an EP is almost always extraovarian.

• The demonstration of a live IUP excludes most cases of ectopic pregnancy, although a con-current ectopic and IUP can still be possible (heterotopic pregnancy); this situation is more likely to be met in patients undergoing infertil-ity treatment.

The presence of a complex adnexal mass, absent IUP and rising serum β hCG levels make the diag-nosis of EP likely.

Free peritoneal fl uid, especially if complex and associated with an adnexal nonovarian mass, increases the likelihood of an EP. The likelihood increases if the amount of fl uid is large (reaches upper abdomen).

US is more sensitive than culdocentesis in detecting haemoperitoneum. The presence of echogenic fl uid, which correlates with haemo-peritoneum, is highly suggestive of EP espe-cially when a large quantity of echogenic fl uid is detected in the presence of an adnexal mass.

Pseudogestational Sac

This refers to the collection of a small amount of fl uid within the decidualized endometrial canal. This is differentiated from a true GS by its cen-tral location (true sac is in one layer of the endo-metrium) and fusiform or tear drop shape with an inferiorly pointing beak (true sac is usually rounded). A pseudosac will not show a double-line sign, YS or an embryonic pole.

Tubal Ring

This refers to a thick-walled cystic structure in the adnexa quite separate from the uterus and ovary and is considered a reliable sign of EP. The tubal ring can mimic a corpus luteum cyst when the ovary is not well seen. A corpus luteum cyst is usually thinner, contains clear fl uid and appears less echogenic than the endo-metrium. Confusion with a haemorrhagic ovar-ian cyst may arise when surrounding fl uid is seen.


Quantitative β hCG

An empty uterus in an at-risk woman in associa-tion with a hCG greater than 1800 IU/L is highly suggestive of the presence of EP. This level of hCG is highly suggestive of EP but is not diag-nostic. It is reasonable to closely follow up rather than treat early stable cases of EP.

Other Biochemical Aids to US Diagnosis

Progesterone is produced by the corpus luteum during the early second trimester, until the placenta takes over production of progesterone. A serum progesterone of <5 ng/mL is 99.8% predictive of a nonviable pregnancy either EP or IUP. Progester-one levels measuring at least 25 ng/mL excludes 97.5% of EPs.

The levels of progesterone are independent of gestational age so that a single test can be diag-nostic without the need for serial examinations.

Endometrial Thickness 0.5 – 1.7 cm

Endometrial changes in the form of a decidual cast occur in 50% of patients and may be indis-tinguishable from IUP. There is no signifi cant dif-ference in endometrial thickness between women with EP and those with spontaneous abortion. A thin endometrium seen on TVS cannot be used to exclude the diagnosis of EP.

Doppler Sonography in EP

High-velocity and low-impedance fl ow is seen in both IUP and EP. Colour Doppler often shows a complete or partial ‘ring of fi re’ sign in an adnexal mass; this has a low-resistance, high-diastolic component on spectral Doppler. Cor-pus luteum has similar fl ow characteristics but this is intraovarian in location while an ectopic is almost always extraovarian.

Spontaneous Resolution of EP

In some patients, an EP resolves spontaneously but the exact incidence is unknown.

The features of EP are depicted in Figure 1-5 .

Endometrial Three-Layer Pattern

A well-defi ned spherical structure forming three hyperechoic layers separated by two hypoechoic layers within the endometrium have been described with EP. However, this sign is con-troversial and has been described in a variety of conditions besides being a normal appear-ance too. The differential diagnosis of the sign includes early IUP and successful implantation in women undergoing in vitro fertilization. It has also been described with trophoblastic regres-sion: symptomatic pregnant patients, clinically stable, serum levels of β hCG levels below a dis-criminatory zone, who lack US evidence of either EP or IUP and when symptoms and serological evidence of pregnancy resolve spontaneously.

DIFFERENTIAL DIAGNOSIS OF EP • Any adnexal mass • All causes of fl uid in the cul-de-sac • Corpus luteum cysts with/without septa • Torsion of ovarian cyst/neoplasm • Endometriosis • Tubo-ovarian abscess • Torsion/degeneration of a fi broid • Ovarian neoplasm • Haemorrhagic ovarian cyst • Uterine leiomyoma • Haemorrhagic subserosal fi broid • Appendix abscess • Diverticular abscess

ULTRASOUND PARAMETERS FOR MEASUREMENT OF GESTATIONAL AGE

Post-LMP Approximate Age (Weeks)

5–6 GS volume 7–12 CRL 12 – 15 BPD, FL, head circumference 24 After 24 weeks, there is variation in

the rate of growth depending upon genetic and environmental factors and ultrasound dating becomes progressively less accurate


A B

E F

G H

DC

FIGURE 1-5 Spectrum of ultrasound fi ndings in EP. The most suggestive fi nding is of a thick-walled echogenic ring-like structure that is extraovarian ( A , B ). On Doppler, there is often a hypervascular area surrounding this, the ‘ring of fi re’ sign ( C ); a YS and an embryo can sometimes be recognizable confi rming the diagnosis ( D ) and a cardiac fl icker can be picked up ( E ). Beware of a small collection in the endometrial canal that can mimic an intrauterine GS ( F ); in fact, this is called the pseudosac of EP. The ectopic can lead to bleeding into the peritoneum and a complex ascites ensues, and echogenic specks, septations and clumps in the ascetic fl uid can form ( G , H ). The white arrow in all images points to the ring-like structure representing the ectopic GS.


GS Size

GS can be visualized from 4 weeks on TVS and a week later on transabdominal scans. The sac is rarely spherical, so a single diameter is likely to be inaccurate and the average of the three diam-eters (AP, transverse and craniocaudal) is used. The inner-to-inner border is used to read off the sac size against standard charts.

Crown – Rump Length

This is the most accurate means of dating a preg-nancy. Fetal attitude, especially considerable fl ex-ion can reduce the reading and the examiner should wait for a more neutral fetal spine curvature before making the measurement. CRL is not affected by most environmental and racial factors.

Biparietal Diameter

This is generally used in the second and third trimes-ters; the accuracy decreases as pregnancy advances.

Femur Length

The FL may be measured from 12 weeks onwards. It compliments BPD measurement and should be used in all cases. In fact, any long bone can be measured but the FL is easiest to identify and measure, making it the most popular long bone.

OTHER FETAL MEASUREMENTS

Abdominal Circumference

This is a bit more diffi cult to measure than the BPD or FL but is useful in assessing the weight of the baby, growth appropriateness or dispar-ity between fetal parameters, IUGR, over growth conditions, etc.

Head Circumference

This is a very useful measurement especially when the fetal head shape exhibits undue narrowing

(dolichocephaly) or undue broadening; both conditions are normal variants but can lead to a misleadingly small or large BPD.

Fetal Weight

Analysis of fetal weight may be performed using standard fetal measurements (AC, HC, FL, BPD, etc.), either singly or in combination. Adding parameters increases accuracy slightly but fetal weight measurement tends to be accurate only within ±10% at best.

Fetal Foot Length

There are limitations to the use of fetal foot length for gestation age assessment particularly in fetuses with growth abnormalities.

The Transverse Cerebellar Diameter

The transverse cerebellar diameter (TCD) is con-sidered as a reliable parameter for estimating the duration of gestation. In IUGR, restriction of the cerebellum is usually spared, making TCD a reli-able indicator of gestational age even when other parameters fall off the appropriate growth curve. Throughout pregnancy, TCD measurements allow for the estimation of gestational age that is independent of the shape of the fetal head and offers potential for evaluation of abnormal fetal growth and anomalous development of the central nervous system.

CAUSES OF INACCURACY IN ESTIMATING GESTATIONAL AGE FROM MENSTRUAL HISTORY • LMP date not accurately known • Cycle is irregular • Cycle is not 28 days long • Bleeding in early pregnancy may mimic a men-

strual period • Contraceptive pill recently used as a form of

contraception • Postdelivery breast feeding


ADVANTAGES OF ULTRASOUND ESTIMATION OF GESTATIONAL AGE • Allows planning for delivery, including deci-

sions for induction of labour and efforts at prolonging pregnancy in cases where the appro-priate period has been exceeded or not reached.

• Is vital for the correct interpretation of screen-ing blood tests such as the triple or quad screen for Down syndrome and other conditions.

• Is imperative for diagnosing fetal growth abnormalities.

CORPUS LUTEUM IN EARLY PREGNANCY The corpus luteum (CL) is identifi ed in the fi rst tri-mester on TVS in most pregnancies. This physiolog-ical structure produces progesterone, which sustains pregnancy until the placenta is formed. At around 7 weeks gestation, the functioning CL is no longer necessary because the placenta assumes hormonal function. Consequently, it decreases in size during 8 – 16 weeks gestation and is subsequently main-tained passively for the rest of the term of pregnancy:

• Varied US appearances with a mean diameter of 1.9 ± 0.6 cm (range 0.8 – 5.5 cm)

• Hypoechoic – 34% • Cystic with thick circumferential wall and

anechoic centre – 27% • Cyst with scattered echoes or internal debris – 23% • Thin-walled simple cyst – 15% • No CL identifi ed – 2% • Circumferential fl ow partial or all CL on

colour fl ow Doppler – 92% • Flow on pulsed Doppler in 92% with a mean

resistive index of 0.49 ± 0.08 (range 0.29 – 0.91)

THE CERVIX IN PREGNANCY

Normal Cervix in Pregnancy

It is usually diffi cult to distinguish the cervix from the lower uterine segment in the nongravid

state and the fi rst trimester. From midtrimes-ter onwards, the amniotic sac clearly defi nes the internal os. US has advantages over digital examination; the internal os can be visualized by sonography and hence early changes of cer-vical incompetence can be detected; moreover, there is a decreased risk of infection and cervical irritation.

Cervical Length

Cervical length is the distance between the internal and external os. The fi rst trimester cervical length is >5 cm. The cervical length decreases to <34 mm at 28 weeks gestation. In patients with multiple gestation, there is sig-nifi cantly shorter cervical length. Normograms have been developed for twins and triplets that help to identify patients at high risk for pre-term labour.

Preterm Labour

There is an inverse relationship between US cervical length and the risk of preterm labour. Length <25 mm at 24 weeks' gestation indicates a fourfold increased risk of preterm labour. Fun-nelling/wedging of the internal os with prolapse of fetal membrane is indicative of the onset of preterm labour. Funnelling of over 60% of the length of the cervical canal is also associated with preterm labour.

Incompetent Cervix

Cervical incompetence is defi ned as cervi-cal dilatation without uterine contractions. In patients with a history of pregnancy loss, it is prudent to establish a baseline cervical length measurement before the gestation age when the previous loss occurred with follow-up scans 1 – 2 weeks depending upon the fi ndings or recent examination or symptoms. TVS com-bined with transfundal pressure or scanning patient in a standing position can illicit early changes.


Dynamic Changing Cervix

This dramatic event can be seen during US exam-ination. The cervix shows dynamic changes with varying degree of funnelling of the internal os associated with vigorous closing and opening of the cervix. These changes occur in the absence of uterine contractions. Although most patients with a spontaneously changing cervix deliver preterm, it is not a sign of imminent delivery and with conservative management delivery may be delayed in some.

Cervical Cerclage

Sonographic guidance can be used to assist place-ment of cervical cerclage as a prophylaxis to pre-term labour in cervical incompetence. Following placement of cervical cerclage, measurements of the canal are made from the internal os to the level of cerclage. Shortening of the upper cervical length <1 cm is associated with preterm delivery.

The Cervix at Term

Several studies using US to evaluate the ripeness and inducibility of cervix have been published and a scoring system has been proposed. Param-eters such as cervical length, cervical diameter and the appearance of the internal os are scored. Using these indices it has been shown that the presence of funnelling and a short cervical length is associated with a shorter duration of induced labour. US has been shown to correlate well with digital examination; however, the fi rmness of the cervix, which is an important sign of the ripeness of the cervix can only be assessed digi-tally. US technique is useful in patients in whom digital examination is contraindicated such as in patients with premature rupture of membranes and unexplained vaginal bleeding.

FALSE-POSITIVE FINDINGS OF INCOMPETENT CERVIX • Uterine contraction – differentiation by the

observation of a thickened myometrium

associated with uterine contractions, palpa-tion of the uterus, placement of tocodyna-mometer and questioning the patient may disclose the presence of uterine contractions

• Narrowed lower uterine segment can mimic funnelling – clarifi ed by observing the cervix over time

• Overdistended urinary bladder impression on the lower uterine segment may produce the impression of funnelling of the cervix

• Cystic lesions such as nabothian cysts and vaginal cyst can mimic a dilated internal os

INCOMPETENT CERVIX: RISK FACTORS • DES exposure in utero associated with cervical

hypoplasia • Previous cone biopsy of the cervix • Prior cervical laceration • Prior cervical trauma – cauterization, dilatation,

curettage etc. • Ostrogen therapy

ABORTION There is 10 – 25% pregnancy loss rate of all clini-cally diagnosed pregnancies. The majority of the losses occur before the seventh week of gestation usually due to abnormal karyotype of which 52% are trisomies, 20% triploidy and 15% monosomy.

Complete Abortion

There is complete loss of products of conception with a closed cervix and a thin endometrium on US.

Incomplete Spontaneous Abortion

There are retained products of conception with continued bleeding associated with a patulous cervix. The retained products may represent pla-cental tissue or fetal tissue. US fi ndings include GS/fl uid collection, GS with a dead fetus, endo-metrial thickness >5 mm in the majority but thickness may vary from 2 to 5 mm; in 14%, thickness may be 2 mm or less. Complications


include endometritis, septicaemia, and diffuse intravascular coagulation.

Inevitable Abortion

The GS becomes detached from its implantation site within the uterus so that abortion becomes inevitable and usually occurs within a few hours. Presentation is usually with PV bleeding <7 days, persistent painful uterine contractions, a dilated cervix and ruptured membranes. US fi ndings include a GS low within the uterus, GS surrounded by an anechoic zone of blood and a dilated cervix.

Missed Abortion

This usually occurs between 8 and 14 weeks gesta-tion. There is a dead conceptus within the uterus usually associated with a brownish vaginal dis-charge with a closed cervix. US features include no cardiac activity in the embryo of appropriate size, gestation inappropriate for menstrual age, GS >25 mm with no embryo, GS >20 mm with-out a YS, misshapen GS, debris within the GS, lack of a double decidual sac, a low sac position ( Figure 1-2 K) and a subchorionic fl uid collection ( Figure 1-2 G – I).

Threatened Abortion

This is fi rst trimester PV bleeding associated with a live fetus and closed cervix. The incidence is 20 – 25% of all clinically apparent pregnancies with a 50% pregnancy loss rate. Fetal viability depends on the detection of fetal heartbeat and movement. Early fetal bradycardia, relative fetal inactivity and the presence of a large subchori-onic haematoma are poor prognostic signs.

FETAL ANOMALIES DETECTABLE ON ULTRASOUND IN THE FIRST TRIMESTER

Head and Neck

• Cystic hygroma • Nuchal translucency

• Anencephaly • Large cranial cysts • Exencephaly • Encephalocele • Acrania • Choroid plexus cysts • Dandy – Walker malformation

Spine

• Neural tube defects • Kyphoscoliosis

Ventral

• Omphalocele • Gastroschisis • Ectopia cordis • Lateral fold defect

Extremities

• Short limb dysplasia

Heart

• Atrioventricular canal defect • Complete heart block

Genitourinary

• Hydronephrosis • Megacystis ( Figure 1-2 M) • Cystic dysplastic kidneys

Placenta, Umbilical Cord and YS

• Partial mole • Umbilical cord cysts • Short cord associated with ventral fold defect • Large YS

Multiple Gestation

• Monoamniotic twins • Twin – twin transfusion syndrome • Conjoined twins


NB . Most fi rst trimester anomalies are more clearly visualized using TVS. Many serious anom-alies may have a normal sonogram in the fi rst trimester of pregnancy – anencephaly becomes obvious after ossifi cation of the calvarium at or after 12 weeks of menstrual age.

FURTHER READING Menstrual Age versus Gestational Age Borrell A , Robinson J N , Santolaya-Forgas J . Report on

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sample chapter differential diagnosis in obstetric and gynaecologic ultrasound 3e by bisset to order...

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