12 spinal dural arteriovenous fistulae

7/25/2019 12 Spinal Dural Arteriovenous Fistulae

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2 Spinal Dural Arteriovenous Fistulae

12.1 Pathology 850

12.1.1

Macroscopic Appearance

851

12.1.2

Microscopic Appearance

853

12.1.3 Pathological Changes in the Spinal Cord

854

12.2 Pathophysiology 854

12.3

Clinical Presentation of Spinal Dural Arteriovenous Fistulae 858

12.4

Imaging of Spinal Dural Arteriovenous Fistulae

859

12.5 Treatment of Spinal Dural Arteriovenous Fistulae 867

12.5.1 Indications 867

12.5.2

Embolization of Spinal Dural Arteriovenous Fistulae: Techniques

867

12.5.3 Results of Spinal Dural Arteriovenous Fistula Embolization

869

12.5.4 Surgery for Spinal Dural Arteriovenous Fistulae

871

12.5.5 Postoperative Follow-up 872

As opposed to the so-called congenital arteriovenous malformations

(AVMs) involving cord an d paraspinal structu res, spinal dur al arteriove-

no us fistulae (SDAVFs) are a cquired s hun ts located within or adja cent to

du ra along the spinal canal. They are by far the mo st frequent arteriove-

no us s hunt (AVS) that o ccurs in older adults. They usually present after

the fourth or fifth decade of l ife, with an 85 (5:l) male predominance

(Tables 12.1,12.2). The reaso n for this male pre dom ina nce at the spin al

level is no t known , an d this domin ance is reversed in d ural an d osteo dur-

a1 AVSs at the skull base a nd sph eno id level, whe re the re is a female pr e-

dominance. The location of the fistula has been rep orted thr ough out the

spinal canal, from the sacr um to th e level of the foram en magn um. The

venous drainage m ay be very extensive and reach th e intracranial dural

sinuses even if th e sh un t is at the sacra l level (Fig. 12.1) o r conversely reach

the thoracic perimedullary venous plexus level from a n intracranial shunt.

Table

12.1.

Age distribu tion in

352

SDAVF and

SCAVM

patients at time of diagnosis

SDAVFs

Mean SCAMVs Mean

Djindjian et al.

1977

130 34 73 52 3 57 26

Rosenblum et al.

1987a

81 25 72 49 4 58 27

Berenstein and Lasjaunias

1992

81 35 87 56 2 42 22

Symon et al.

1984 60 29 75 57 14 40 31

SDAVF, spinal dural arteriovenous fistula; SCAVM, spinal cord arteriovenous mal-

formation.


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850


Fig. 12.1A-E. Progressive thoracic myelopathy. MRI investigation (A,

B)

shows evi-

dence of increased signal changes in the cord extending up to the mid-thoracic level

(arrows) and prominent flowvoids,in particular along the dorsal aspect of the spinal

cord. Angiography shows this was caused by a spinal dural arteriovenous fistula fed

by the lateral sacral artery C),with retrograde venous drainage via the sacral radic-

ular vein (arrows) toward the dorsal perimedullary venous plexus at the conus level

D,

E)

Table 12.2. Sex and age distribution in 172 patients with SDAVF

(Patients) Male Female Mean age

Djindjian et al. 1977 46 38 6 52

Merland et al. 1980a

13 10 3 59

Symon et al. 1984 55 49 6 57

Rosenblum et al. 1987a 27 23 4 49

Berenstein and Lasjaunias 1992 31 25 5 56

Total 172 145

(85 )

25 (15%) 55

SDAVF, spinal dural arteriovenous fistula.

a

Includes Kendall's first ten patients.

12 1 Pathology

An SDAVF is an abnormal arteriovenous shunt in the dura, most com-

monly at the level of the intervertebral foramen (Kendall and Logue 1977;

Merland et al. 1980b; Symon et al. 1984; Rosenblum et al. 1987a). The

arterial supply mostly arises from a dural (radicular) branch of the dor-

sospinal artery (seeVol. 1) in the region of the intervertebral foramen. The

spinal cord veins (in contrast to the arteries) can pierce the dura quite far

from a nerve root. In this venous disposition, a potential bimetamere


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Macroscopic Appearance 85

Fig. 12.2A-C. Spinal dural arteriovenous fistula supplied by intersegmental dural

anastomosis. Angiography of intercostal artery at T6

A )

demonstrates radicular

supply

short arrow)

towards SDAVF long

arrow)

with reflux down the interseg-

mental anastomosis double arrows).Angiography of intercostal artery

T7

B) shows

radicular supply to the SDAVF via

the

same intersegmental anastomosis double ar-

rows).

Injection of liquid glue via T6

C )

shows deposition of embolic material down

the intersegmental anastomosis as well as across the arteriovenous fistula toward the

perimedullary venous plexus of the spinal cord, resulting in permanent obliteration

of the shunt and good clinical outcome

arterial supply to the dura l arterioven ous fistula DAVF) can be de m on-

stra ted Figs. 12.2,12.3). However, in th e great m ajority of patien ts, there

is a single extradural arte rial pedicle tha t gives rise to a small som etimes

microscopic) shu nt that is within the d ura itself. From this sh unt, a highly

tortuous, single dr aini ng vein em erges. This vein pierces the dura several

millimeters from the accompanying nerve root either above or below it)

to reach the perim edullary venous system Benhaim et al. 1983) an d then

produc es venous hypertension of the medullary veins see Sect. 12.2).

12 1 I Macroscopic ppearance

The nidus of the DAVF can be located anyw here along the d ura bu t is mos t

commonly situated near th e nerve root exit. The abno rma l arteriovenous

shu nt is usually not readily visible using a n extrad ural surgical approac h

Benhaim et al. 1983).

The spinal radicular veins enter the dura close to the nerve root in

60

of patients a nd away from the ne rve root in 40 . Shu nting of arterialized

blo od from the DAVF into the radicu lar vein causes reversal of flow in this

vessel, resulting in enlargement of the radicular vein in the intradural

space. The ascending vein is usually a single, dilated, tortuous channel

that reaches the perimedullary venous netw ork most frequently on the

dorsal surface of the spinal cord. Patients with both p osterior an d anteri-

or medullary drainage tend to have more severe symptoms than those


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852 12 Spinal Dural Arteriovenous Fistulae

Fig. 12.3A-D. 48-year-old female patient presented with slowly progressive tho-

racic myelopathy and MRI compatible with venous congestion from spinal dural ar-

teriovenous fistula SDAVF). Spinal angiography demonstrates dual supply from T8

A) and T

B)

toward the intersegmental dural anastomosis small arrows), which in

turn supplied the DAVF arrowhead). Selective catheterization of the radicular artery

at the T8 level C) and embolization with glue resulted in deposition of the embolic

material just proximal to the fistulous communication arrowhead). Immediate

follow-up angiogram at the T level shows the continued opacification of the fistula

arrowhead) from the radicular artery at that level D), indicating the lack of venous

penetration of the embolic material. Surgical disconnection was achieved 2 days later

by dividing the radicular vein intradurally, resulting in good clinical recovery


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Microscopic Appearance 853

with exclusively posterior drainage. The subseque nt direction of the per-

imedu llary venous drainag e is most often upward toward the thoracic and

cervica l levels.

12 1 2 Microscopic Appearance

The dural feeding) arteries originating at the sacrolum bar or thoracic

levels often divide into small branche s an d then merge into a single artery

before entering the shunt. These sm all arteries show no structural abn or-

malities.

The large d rainin g radicular vein is always single, intradural, an d u su-

ally very dilated and to rtuou s, with irregular partia l thickening an d vari-

able luminal na rrowing. The no rm al d orsal medu llary vein is rarely single

at the tho raco lum bar level see Vol.

1

but normally divides into three

channels of a sm aller caliber at the lower mid-tho racic level. Due to th is

normal disposition of venous architecture with limited venous outflow

capacity, recru itme nt of add itional venous drain age often involves the

vasa corona an d dors olatera l spinal venous channels. Wall thickening of

these venous channels, wh ether circumferential and /or limited to a cush-

ion-like plaque, is nearly always present. Such thickening frequently in-

volves the in tim a an d/or the media. Atherosclerotic changes a nd calcifi-

cations can som etimes be fou nd in the veins. Stenosis to near complete

occlusion is also found i n so me segments.

Various stages of thrombosis can be see n, which may ran ge from oc-

clusion to full recanalization. Similar changes have been described as a

frequent incidental finding at autopsy.

In general, the arteriovenou s comm unication is microscopic a nd the re-

fore may be difficult to identify at surgery. Benhaim et al. 1983) were able

to ob tain two spec imens of the fistula itself. Exam ination revealed the vas-

cular lesion to be situated within the d ura m ater. The struc ture of these

fistulous vessels was not t ha t of no rm al veins or arte ries. Som e of th e ves-

sel wall will appea r similar to th at of arteries, with a lam ina elastica inter-

na LEI), prom inent sm ooth m uscle cells, poor connective tissue, an d a

thick a nd rig id wall. The LEI frequently divides in to two o r mo re layers of

elastin; mu scular atroph y an d increased connective tissue w ere present

in the media. Other vessels looked more like veins without evidence of

anom alous changes in the media. Still othe rs looked like veins with no

LEI, much more connective tissue, and a rather t h i n ~ n dlexible wall, with

modifications such as irregular thickening due to collagen and /or elastin

fibrosis an d hyp ertroph y of sm oo th muscle cells. Interestingly, Benhaim

et al. 1983) found no calcifications or throm boses in the arteriovenous

fistula and in both specime ns they were able to describe a free comm uni-

cation between vessels of different stru cture . The arteriovenous s hun t

could be seen in serial sections, demonstrating two arterial structures

anastom osing and m erging with a small-caliber vein thro ugh a sho rt,nar-

row channel.

The histological description, and in particular the ap pearance of the

draining vein, would suggest evidence of a d ystrophic aspect rathe r tha n

a dysplastic lesion, with changes sec ondary to local venous hy pertension


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85

2

Spinal Du ral Arteriovenous Fistulae

resulting fro m the arterio veno us shunt. The histological changes seen in

these veins are very similar to those seen in saphenous veins used for

coronary bypass grafts. The atherosclerotic and calcific changes in the

veins are also quite compatible with a n acqu ired lesion.

12 1 3

Pathological Changes in the Spinal Cord

Extensive pathological ch anges may be p resent w ithin th e cord itself, even

thou gh the prim ary s tructural abnormality is entirely extramedullary. In

advanced lesions, histological abnormalities are evident throughout the

cord. The changes particularly involve the lateral corticospina l tract an d

appear to spread gradually into adjacent po rtions of th e white m atter of

the lateral funiculus. More advanced changes progressively involve the an -

terior g ray matter an d the posterior columns. Gillilian (1970) pointed out

consistent sparing of the anterior median segment.

A

typical feature in

long-sta nding advanced lesions is the app earance of neocapillaries with-

in the co rd itself. This particular change has be en confused with the pres-

ence of an arteriovenous nidus. Our curren t unde rstandin g of the venous

anatomy an d the pathophysiology of the disease ha s taught us that these

neocapillaries are primarily the congested intrinsic veno us netwo rk of the

spinal cord. This is different from secondary neovascularization, which

will result from chronic an d extensive hypoxia secon dary to lon g-stand-

ing venous congestion (sprouting angiogenesis from venules) (Folkman

1975). The en d stage of this venous congestion, venous ischemia a nd its

impact on th e spinal cord, will be similar to th e syn drome described by

Foix and Alajouanine (1926).

12 2

Pathophysiology

In 1972, Manelfe et al. describ ed a glom erulus-like s truc ture tha t he called

peloton vasculaire

or vascular balls (Fig. 12.4). These a re n orm al vascular

stru ctu res, usually situated between two layers of th e du ra mater. In his

specim en, usually two o r mo re afferent arterioles converged into this vas-

cular ball and d rain ed thro ug h a single vein located intradurally. Unfor-

tunately, in Manelfe s specim en the du ra mater w as transected an d the

vein could n ot be followed. These no rmally pres ent stru ctures, which we

will call the glom erulus of Manelfe, can rou tinely be fou nd in th e upp er

lum bar o r dorsal regions but are absent at the cervical level. The strikin g

resemblance between the glom erulus of Manelfe an d the SDAVF was no t-

ed by Merland et al. (1980a). The form er structu res are believed to have

the function of preserving co nstant venous pressure in the spinal cord, re-

gardless of changes in intra- abd om ina l or intrathoracic pressure. There-

fore, it appe ars tha t SDAVFs may result fro m a loss of the no rm al phy sio-

logical control of this system.

However, if this were the sole mechanism responsible for SDAVFs

one would expect the co ndition to occur far more frequently. Therefore,

additional factors must also contribute to the development of these fis-

tulae.


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12 4

Glomerulus of

e specimen rem oved

dura of the

on with

l, demon -

ike stru c-

(arrowhead) situated be-

rs of the du ra

. Note the two afferent ar-

ching into

with a single

g vein tha t has been cut.

our tesy of Prof. C. Manelfe)

Pathophysiology 855

Tadie et al. (1985), n their stu dy of the m orpho logical functional ana to-

my of the spinal cord veins, demo nstrated tha t the lumbar and lower tho-

racic portion s of the spinal cord normally dra in cephalad into the radicu-

lospinal veins ,w hich are sm all in caliber (see Vol. 1). This m akes dra inage

from the lumbar and thoracic cord somewhat tenuous and sensitive to

hemodynamic alterations. At the cervical level, symptomatic SDAVFs are

extremely rare, since the venous drainage is divergent and therefore fa-

vorable, in contrast to the convergent lumbothoracic venous drainage

(Mo ss et al. 1989).

During normal physiological changes of intra-abdominal and/or in-

trathoracic pressu re (Valsalva, defecation, respiration, etc.), the pressu re

in the spinal cord veins remains constant. Furthermore, Tadie claimed

tha t it is impossible to inject th e spina l veins from th e periphery. To ex-

plain this, various investigators have postu lated th e presence of valves in

the spinal venous system (Lazorthes 1978), although n o anatomical proof

can be provided.

Tadie, in his histological sections, was also u nable to find a ctual valves

in the spinal veins. He did, however, demonstrate an imp ortant narrowing

of the radiculospinal veins at the point where they cross the dura mater.

At this p oint, the vein loses its own wall, which is replaced by a n arac hnoid

cuff and by the dura itself. In addition, as the vein enters and exits the

dura, it does s o in a zigzag fashion. Tadie postulated that, under norm al

physiological conditions, the narrowing and zigzagging opposes any

blood flow from the p eriphery into th e intradu ral space, so that blood flow

is only pe rm itted in the physiological direction. Such a configu ration is a

consistent disposition at the norm al sino du ral junction. If the venous

pressu re were to increase abnormally, the n the ara chno id cuff would be-

come engorged a nd o bstruct the vein. In add ition, a glomerulus-like struc-

ture (similar to the glo me rulus of Manelfe) was demo nstrated at the point

where the no rma l dra ining vein crosses the dura m ater. These observa-

tions have led to the term the protective anti-back flow system.


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856


Fig 12.5A D. Legend see p 857


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Pathophysiology 857

Fig. 12.5A-F. Spinal dural arteriovenous fistula SDAVF): anterior spinal artery and

vein circulation.

A

Mid-arterial phase. B Late phase of the left T1 intercostal artery,

which gives rise to the spinomedullary artery; this phase failed to demonstrate the

radiculospinal vein.

C

Superselective injection of the right

L

lumbar artery demon-

strates the SDAVF arrowhead), the single ascending draining vein curved arrows),

and the ascending venous drainage.

D

Plain film shows the radiopaque acrylic depo-

sition with occlusion of the dural lesion and the first centimeter of the ascending

draining vein white curved arrow).

E, F

Postembolization follow-up angiogram of

the anterior spinal axis shows normal arterial

E)

and venous F) circulation time af-

ter treatment, with opacification of the radiculomedullary vein compare to A and B)

During selective spinal angiography, following the injection of the

anterior spinal artery, one can routinely dem onstrate the drainage of the

spinal cord into the radiculospinal veins. In SDAVFs, such spinal cord

draina ge is delayed Fig. 12.5) an d the venous re tu rn of the DAVS usually

takes an ascendin g course toward the cervical and/oraintrac ranialregions.

Furthermore, maneuvers that change intra-abdominal or intrathoracic

pressure can aggravate sym ptoms in this co ndition. Tadie has proven that

in SDAVFs one can reflux into the spinal veins from extrasp inal injections,

testifying to an im paired venous protective system.

In on e of ou r patients, an ab norm al shunt at the e pidural level was not-

ed as causing root pain at that time. Some 4 years later, with venous

draina ge towards the me dullary veins, the patient developed a myelopathy.

An additional factor to consider is the requirement that a preexisting

restriction of the venous drainage of the spinal cord a nd /or meninges m ay

be present to make the acquired SDAVF symptomatic. The presence of

throm bosis a nd recanalization seen pathologically is consistent with the

pathophysiology of intracranial dural AVMs.


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8 8 2 Spinal Dural Arteriovenous Fistulae

Thiebot et al. 1986) rep orte d the case of a 24-year-old female patient

with mu ltiple SDAVFs dra inin g into spinal veins withou t venous restric-

tions or flow impairment. The patient had exhibited minimal nonpro-

gressive symptoms since childhood and was followed for an additional

years. The an giog raphic studies in this patient showed m ultiple SDAVFs

with vascular stru ctur es similar to the glom erulus of Manelfe. Clear arte-

riovenous shunting was noted in the angiogram s but no associated ou t-

flow restrictions w ere seen. The lesions draine d throu gh spinoradicular

veins. This finding is highly suggestive of a congenital anom aly of the no r-

ma l anti-back flow mechan ism de scribed by Tadie et al. 1985).In con trast

to the acquired sym ptom atic) typ e of SDAVF, this lesion was in a very

young patient, the arteriovenous fistulae were multiple and only in the

thoracolumbar area), the paraspinal venous drainage had a normal ap-

pearance, and an unimpaired, normal-to-increased medullary transit

time was present without stagnation.

The usual clinical findings of the slowly progressive mixed m oto r an d

senso ry myelopathy are reversible if pro perly treated in its early stage, al-

tho ug h its effects may become irreversible in later stages wh en it is asso-

ciated with a necro tizing myelopathy. This m yelopathy can be explained

by chronic venous hypertens ion Am inoff et al. 1974b; Merland et al.

1980a; Sym on et d 1984).

The arteriovenous shunting into the coronary venous plexus of the

spinal cord m ay extend to the dorsal and /or ventral surface of the cord.

Extension m ay also occur up ward to the cervical or intracranial d ural si-

nuses. One will not see the radicular spinal veins at the lum bar o r thoracic

area d rain ing these lesions o r the sp inal cord itself. As the p ressure in the

venous system increases, it is progressively tran sm itted toward the intr in-

sic veins of the sp inal cord, ma inly those of the postero lateral white ma t-

ter a nd lateral corticospinal tract, an d subs eque ntly affects the lateral fu-

niculus, posterior column, and anterior gray. The relative sparing of the

anterior median segment of the spinal cord is probably related to the

anatomical organization, which preserves the central veins a nd of the a n-

terio r me dian sp inal vein Symon et al. 1984).

Venous hypertension reduces the arteriovenous pressure gradient an d

decreases tissue perfusion, resulting in progressive hypoxia to the spinal

cord. The raised venous pressure further decreases blood flow by pro-

ducing progressive intramedullary vasodilatation, with possible progres-

sive exhaus tion of auto regu lation in the affected areas. Progressive vas-

cular dilatation in this uncontrolled fashion reaching the capillaries re-

sults in the transmission of un dam ped pulsations to the cord, decreased

tissue perfusion with edema formation, and progressive loss of cord tis-

sue function.

12 3

Clinical Presentation

of Spinal Dural Arteriovenous Fistulae

The clinical presen tation of DAVFs ha s been docum ented in various series

in the literature Kendall an d Logue 1977; Merland et al. 1980a; Djindjian

1978; Symon et al. 1984; Rosenblum et al. 1987a) and was documented


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Imaging of Spinal Dural Arteriovenous Fistulae 859

Table 12 3 Symptoms of spinal dural arteriovenous fistulaea

Symptoms Initial symptoms ( ) Symptoms at diagnosis ( )

Back andlor root pain 28

7

Paresis 40 88

Impotence 43

Bowel disturbance 4 75

Bladder disturbance 5 85

Hemorrhage 0 0

Total number of patients 172. Based on Djindjian et al. 1977; Merland et al 1980a;

Symon et al. 1984; Rosenblum et al. 1987a; Berenstein and Lasjaunias 1992.

in the first edition of this book (Vol. 5,Chap. 1 (Tables 12.1-12.3). Sub-

sequently, additional series an d case reports have been published (Bru-

nerau et al. 1996;Hu rst et al. 1995; an D ijk et al. 2002).

There is a

5:l

male-to-female ratio in SDAVFs and age ranges from

25 o 78 years. The vast m ajority of th e patien ts, however, were o lder th an

50 years of age at the time of presen tation, an d the average age at presen -

tation was 68 n th e van Dijk series (2002).

In van Dijk s series the clinical hist ory show ed th at th e first signs of

DAVFs were sp astic ga it in 55 , paresthesias in 47 , and pain in 33 . The

time interval between initial symptoms and diagnosis was on average

10.5months.

At the time of presen tation for medical consultation, leg weakness o r

paraparesis was documented in 96 , sensory numbness or paresthesia

occurred in

9096,

rinary incon tinence or retention in

82

bowel prob-

lems in 65 , and pain in 55 of patients. Sexual dysfunction is a freque nt

presenting symptom but often not discussed and poorly recorded. In-

tradu ral hemo rrhage, as a rule, does not occur with SDAVFs but has b een

repo rted in exceptional circumstances (D o et al. 1999).

12 4


Advances in noninvasive imagin g have greatly contributed to ou r ability

to estab lish the timely d iagnosis of sp inal DAVFs. The role of plain films,

myelography, and computed tomography has been taken over by MRI,

which reliably demonstrates the presence of signal changes within the

cord, signifying th e im aging equivalent of the clinical symptom atology.

The absence of significant mass effect and the nonspecific slight en-

hancem ent following intravenous contrast administration all favor the

non neop lastic or nondem yelinating cause of these MRI findings (M asaryk

et al. 1987;Gilbe rtson et al. 1995). n addition, abnorm al flow voids can be

seen, representing the p rom inen t perimedu llary venous system associat-

ed with the retrograde venous reflux from the DAVE These findings on

MRI are nonspecific for the actual location of the du ral fistula (Figs. 12.1,

12.6) but are highly specific for their inipact. Epidural, dural, and per-

imedullary AVSs may all produce similar MRI findings, and therefore

their clinical symptoms may also be similar (Figs. 12.7-12.9). Spinal


12/24

860

2 Svinal Dural Arteriovenous Fistulae

Fig 12.6A,

B A 52-year-old

man presented with a 5-month

history of progressive thoracic

myelopathy.MRI

A )

shows

increased signal changes with-

in the thoracic spinal cord

arrows)and possible flow

voids along posterior aspect of

the cord. Spinal angiogram

with verification of the anterior

spinal axis at the thoracic level

showed delayed venous phase

requiring a search for a dural

arteriovenous fistula which at

the time of a second angiogram

B) was shown to be located at

the foramen magnum and fed

by the ascending pharyngeal

artery and to be draining

downward toward the cervical

and thoracic levels

arrow)

Fig 12.7.

Epidural arteriove-

nous shunt at the low thoracic

level

long arrow)

with drainage

outward toward the hemia-

zygos system short arrow) as

well as toward the epidural

venous plexus within the spinal

canal double arrows) and asso-

ciated with retrograde pial

spinal cord venous drainage

arrowheads)


13/24


86

Fig. 12.8A-C. A 72-year-old

man presented with a 2-month

history of progressive myelopa-

thy. MRI A )demonstrates evi-

dence of prominent flow voids

arrows)along posterior aspect

of the cord and increased sig-

nal at the conus level. Selective

angiography into the lateral

sacral artery double arrows, B)

shows arterial supply short

arrows) converging toward

an epidural sacral arteriove-

nous shunt

arrowhead)

drain-

ing toward the epidural venous

plexus

open arrowhead) .

C Drainage toward the ascend-

ing lumbar venous system was

noted as well as reflux toward

the sacral radicular vein which

drained cranially toward the

conus along the

R

S1 nerve root

long arrow)

angiography will be n eeded to sepa rate out these different etiologies an d

establish the exact nidus location of the

AVS

mprovements in MR ech-

nique Farb et al. 2001,2002) have resulted in o ur ability to noninvasively

demon strate the actual location of the

AVF

along the dura , which, when

presen t, will help focus the spinal ang iogram on a specific segmental level

Figs. 12.10,12.11).

Spinal angiography is done when MRI has demonstrated evidence

compatible with a venous congestive myelopathy as the explanation for

the clinical symptomatology. While in the past the a ngiogram w as done as

pa rt of the investigative process, nowadays it is don e with th e diag nosis of


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862

12 S ~i na l ural Arteriovenous Fistulae

Fig. 12.9. Paravertebral epidural arteriovenous malformation presenting with my-

elopathy which on MRI A) shows evidence of increased signal changes within

the spinal cord

arrow).

At selective angiography B, C), this proved to be related to

retrograde radicular venous drainage from the epidural venous plexus open straight

arrow)

to the perimedullary veins of the cord

arrows).

The draining vein was surgi-

cally clipped

arrows,

D to disconnect the epidural venous system from that of the

spinal cord leaving the epidural arteriovenous shunt to continue to drain toward the

paravertebral hemiazygos venous system

open curved arro w)

DAVF already strongly suspected or even confirmed by MRI. It can there-

fore be more efficient and focused on the potential for endovascular treat-

ment. It remains important to assess the blood supply to the spinal cord

and in particular the origin of the main supply to the anterior spinal ar-

tery radicular-medullary arterial supply). This will allow for assessment

of the circulation time within the spinal cord, which should be delayed if

the myelopathy is caused by venous congestion Fig. 12.5) Launay 1979;

Merland et al. 1980; Merland and Reizine 1987; Willinsky 1990b). It has

been our routine to iniect nonionic contrast material at 1 ccls for 10 s into

the intercostal or lumbar artery that supplies the anterior spinal axis

radicular-medullary arterial system). Delayed opacification of the venous

phase perimedullary and radicular-venous systems) of the region sup-

plied by the anterior spinal artery) beyond 20 s confirms the probable ve-

nous cause of the myelopathy. If the myelopathy is at the cervical level the

cervical anterior spinal axis should be examined rather then the radicu-

lar-medullary arterial system at the thoracolumbar level.

Another important reason to examine and to establish the origin of the

anterior spinal artery is that it can be located at the same level as the radic-

ular supply to the dural fistula. This information may preclude safe en-

dovascular treatment of the DAVF Figs. 12.12,12.13) Agarwal et al. 1992).

While the majority of the DAVFs are located in the dura adjacent to the

nerve root, occasionally the location is along the dura between two adja-

cent nerve roots intersegmental). This will invariably result in dual arte-

rial supply to these types of DAVSs and make it imperative at the time of

treatment to reach the venous outlet of the shunt, as otherwise the shunt

will continue to be fed by the untreated arterial pedicle.


15/24

Imaeine of Spinal Dural Arteriovenous Fistulae

86

12.10. Example of contrast-

nced MRI axial view,

f the intercostal ar-

appearance A) and

f spinal dur-

1 arteriovenous fistula SDAVF,

A prominent vascular chan-

level long arrow)

raining radicular vein

an SDAVF at the foramen

el refluxing toward the

of the spinal cord short

12.11A, B. Example of con-

d MRI coronal

w, A) in a patient investigat-

le spinal dural

riovenous fistula SDAVF),

channel arrow) entering

bral foramen as well

l canal.

e angiography of the

el demonstrates excellent

presence

DAVF arrow) and the re-

towards

dullary venous

While the location of the DAVF can b e anywhere along th e du ra, a cer-

vical localization is extremely u ncom mo n. In the Toronto series (v an Dijk

et al. 2002), the mo st frequent location was mid-thorac ic and 70 of

DAVFs were located on the left side. It is also accepted tha t the loca tion of

the dural shunt m ay be at the level of the foram en magn um or even in-

tracranial (Figs. 12.6,12.14) an d yet present w ith spina l cord myelopathy

due to the rerouting of the venous drainage of the sh unt toward the per-

imedullary venous system of the spinal cord (Willinsky et al. 19 9 0 ~ ; a-

hagne et al 1992; Bret et al. 1994). Par t of the ang iograph ic pro toco l


16/24

864

12

Svinal Dural Arteriovenous Fistulae

Fig. 12.14A,

B

Intracranial dural arteriovenous malformation at the level of the left

vetrous bone and drainage into the anterior and posterior spinal medullary veins.

The patient presented with progressive myelopathy involving the lower extremities

and sphincter dysfunction. A Cervical myelographic examination demonstrates pro-

.

minent vascular structures arrows).

B

Lateral subtraction angiogram of the supers-

elective injection of the stylomastoid artery small arrow). The site of fistulization is

at the basal tentorial edge of the cerebellopontine angle arrowhead), draining into

the petrosal vein curved arrows) and reaching the anterior and posterior medullary

veins long arrows). There is also reflux into cerebellar vermian veins and drainage

into the straight sinus curved arrows). Note filling of the middle meningeal artery

via its tentorial branches

Fig. 12.12A-D. A 48-year-old

woman presented with pro-

gressive myelopathy of several

months duration. MRI A)

shows evidence of increased

signal changes within the spinal

cord and prominent flow voids

along the dorsal and ventral

aspect of the cord. Angiogram

at L2 B) hows evidence of

opacification of spinal dural ar-

teriovenous fistula SDAVF) on

the left side arrow). Selective

catheterization of the radicular

branch of the

L2

lumbar artery

C,

D) shows that the same

radicular artery supplies the

AVF and the spinal c6rd radi-

culospinal artery, arrows), a

contraindication for endovas-

cular treatment


17/24


865

Fig. 12.13A,

B.

Selective angiography into the radicular branch of the L2 lumbar ar-

tery demonstrates supply to both a spinal dural arteriovenous fistula long arrow,A

and the anterior spinal axis radiculomedullary spinal artery, short arrows,B , a con-

traindication to endovascular treatment

Fig. 12.14A, B. Legend see p. 86


18/24

8

12

Spinal Dural Arteriovenous Fistulae

Fig 12.15A C. Multifocal spinal dural arteriovenous fistula SDAVF).A Selective in-

jection of the left T10 fills the radiculomedullary artery and an SDAVF on the level

above the

arrowhead,

draining into the anterior spinal vein

arrow).

Late phase of

the same injection. Note the descending and ascending drainage

arrows)

and the

dilution at the highest level

curved arrow).

C

Injection of T7 shows a second dural

lesion double arrowhead) draining cephalad. Note downward drainage to the same

vein that drains the TI0 lesion

long arrow)

and the exact site of venous anastomosis

curved arrow)


19/24

Embolization of Spinal Du ral Arteriovenous Fistulae: Techniques 8 7

while investigating patients suspected of harboring a DAVF is to assess

the in tra- an d extracranial circulation, in particular when no shunt can be

identified at the thoracic, lum bar, or sacral levels.

Multiple DAVFs in the same patient at the sam e time or o ccur ring over

time a re exceptional Fig. 12.15) Pierot et al. 1993; Chaloupka et al. 1995)

an d they occur mu ch less often th an in intracra nial DAVFs.

Spontan eous closure of an SDAVF witho ut tre atm en t is extremely rare

Meder et al. 1995 ).

12 5 Treatment of Spinal Dural Arteriovenous Fistulae

12 5 1 Indications

The presence of a n SDAVF is an excellent indication for trea tmen t in all

patients, as the risk of endovascular or surgical treatm ent is m inim al and

the possible benefits a re significant. This applies even to patients prese nt-

ing with what appear to be fmed neurological deficits.

12 5 2 Embolization of Spinal Dural Arteriovenous Fistulae: Techniques

The m ain objective of SDAVF treatm ent is to occlude the d rain ing radic-

ular vein as it exits from the arteriovenou s shu nt, thereby insu ring dis-

connection of the microfistula from the spinal cord venous system. It is

occluded at the time of em bolization) within the first millimeters of the

exiting vein Figs. 12.16, 12.17) or at the time of surgery) prio r to its

ope ning into the pial netw ork Fig. 12.9). In sacral lesions, the long dra in-

ing vein can be occluded over several centimeters, as it on ly reaches the

me dullary veins at the conus level. The on ly significant contraindication

to endovascu lar treatm ent of SDAVF occu rs in those pa tients in who m th e

anterior or po sterior spinal artery originates from the sam e pedicle as the

SDAVF Figs. 12.12,12.13) Merland et al. 1980a,b; Agarwal et al. 1992).In

the g reat majority of p atients, emb olization can close the lesion in a very

safe man ner.

In view of the small size of the afferent arteries a nd th e fistula itself in

the 40-60 pm range), only a low-viscosity liquid agent will reach th e nidus

an d the proximal vein. Particu late agents, such as polyvinyl alcohol PVA)

or d ura mater, will not b e effective o r may only give tempo rary good re-

sults. Alm ost invariably their use results in recanalization and recurr ence

Hall et al. 1989; Morgan a nd Marsh 1989).Particles will no t pen etrate ef-

fectively o ob tain complete cure and we consider them contraindicated in

the endovascular management of SDAVFs.

Closure of SDAVFs using a liquid em bolic agent is best accomplished

with a mixture that will have a long polymerization time, such as

1,

N-butyl-cyanoacrylate NBCA) with

2 3

iophendylate lipiodol). The in-

jection can be do ne with a simple superselective catheter or with a coaxi-

al assembly system. The acrylic-iophendylate mix ture can b e injected in

a

continuous colum n or using a so-called sandwich or push technique. The

technical goal of therapy is occlusion of both the nidu s an d the proximal

po rtion of the afferent vein.


20/24

8 8


Fig 12.16A-D. Spinal dural arteriovenous fistula SDAVF) of the sacrum. A Angiog-

raphy using a coaxial system with a variable stiffness microcatheter

arrow)

demon-

strates the arterial component

small arrows)

and the site of shunting

arrowhead)

with its ascending venous drainage curved arrow).Note the retrograde filling of the

contralateral dural supply to the sacrum arrow). Later phase of the same injection

with better filling of the right lateral sacral artery

large arrows).C Digital subtrac-

tion angiography image of the acrylic deposition at the time of embolization shows

the cast of the SDAVF as well as the proximal aspect of the radicular vein

arrowhead)

and the distal segment of the right lateral sacral contribution. D Follow-up left inter-

nal iliac injection. There is no filling of the SDAVF and good opacification of both the

right lateral sacral artery arrow) and the medial sacral artery large arrow). This

confirms that there is no fdling of the lesion


21/24

Results of Spinal Dural Arteriovenous Fistula Embolization

869

Fig. 12.17. Spinal dural arteriovenous fistula SDAVF) shown at 3-D digital subtrac-

tion angiogram on frontal view A) and axialview (B) to be located at T12 left side)

and supplied by the radicular artery longarrows) and to be draining first toward the

ventral medullary venous plexus short arrows). C G see p. 870

As in o the r anatom ical locations, the collateral circulation of the dura

of the involved region m ust be exam ined for the presence of natural arte-

rial co llaterals: ipsilateral above and below th e level of th e fistula as well

contralateral at the sam e level of the DAVF an d repeated on the imm edi-

ate postem bolization studies (Fig. 12.3).

The absence of radicular vein opacification at the tho racic level, du ring

the ascending venous d rainage phase of a thora colum bar or lumbosacral

SDAVF migh t favor the use of hepa rin following embolization. Similarly,

patients w ith descending venous drainag e in a thoracic SDAVF may bene-

fit from postembolization anticoagulation the rapy for at least several days.

As opposed to th e treatmen t of spinal epidural AVFs,;here is no role for

the venous endovascular app roach to SDAVFs (Willinsky et al. 1993).

12 5 3

Results of Spinal Dural Arteriovenous Fistula Embolization

Nimii et al. (1997) (49 cases), Song et al. (2001a) (27 cases), W estphal and

Koch (1999) (47 cases) and van D ijk et al. (2002) (49 cases) reported the

initial success rate of endovascular trea tm ent with liquid adhesive embol-

ic materials to vary between 25 an d 90 of all cases. Nim ii et al. (1997)

considered penetration of the liquid adhesive into the fistula without pe n-

etration into the proximal vein as adequate, which is reflected in their

high re currence rate of 23 . Song et al. (2001a) reported a failure rate of

25 , bu t follow-up angio graph y was don e in only 65 of the patients.

Up to 80 of patients will show clinical benefit from this f orm of treat-

me nt, ranging from clinical improvem ent of various degrees to stabiliza-


22/24

87

2

Spinal Dural Arteriovenous Fistulae

Fig 12.17C G.

Legend see

p

871


23/24

Surgery for Spinal Dural Arteriovenous Fistulae

87

tion. Merland and Reizine (1987) reported on 63 patients treated at Lari-

boisiere Hospital (27 operated on and 36 embolized). In 50 of patients,

there was a significant improvement of symptoms, in 20 only minor im-

provement occurred, in 16 the progressive myelopathy stabilized, and in

4

there was an aggravation or continued deterioration. Clinical im-

provement was noted in days, weeks, or within 3 months. The best results

were seen in patients with the shortest time between onset of symptoms

and treatment. Clinical improvement occurred primarily in motor func-

tion, deep sensory function, and strength. Superficial sensation and

sphincter improvement was noted later and was less satisfactory. These

results are similar to those reported by Merland and Reizine (1987), Barth

et al. (1984), and more recently by Song et al. (2001b). Significant im-

provement in motor and bladder function was also demonstrated by van

Dijk et al. (2002), with a mean follow-up of 32.3 months. Song et al.

(2001b) demonstrated that if the patient was treated within 13 months of

symptom onset, improvement in gait and to a lesser extend bladder func-

tion could be anticipated.

Complications associated with endovascular treatment could be related

to the failure to recognize that the same radicular artery supplying the

AVF is also contributing to the supply of the anterior or posterior spinal

arterial systems with inadvertent embolization of this supply.Another po-

tential cause for complication is the inadvertent deposition of the embol-

ic material beyond the nidal-venous junction and into the perimedullary

venous system of the spinal cord, causing thrombosis of the spinal cord

venous system. Both these potentially devastating complications are

avoidable with proper analysis of the anatomical situation and choice and

method of injection of the embolic material. Recent experience by well-

trained teams has shown the complication rate associated with endovas-

cular treatment to be extremely low or even absent (van Dijk et al. 2002).

12 5 4

Surgery for Spinal Dural Arteriovenous Fistulae

If endovascular therapy is unsuccessful, surgery should be performed

during the same hospital stay. As indicated above, the goal of surgical

treatment will be the same: disconnection (transection, division) of the

radicular vein as it runs intradurally from the dura toward the spinal cord

perimedullary venous plexus (Fig. 12.13).

Fig. 12 17

continued).

Selective angiography in to the intercostal artery C-E) showed

radicular branches to be converging toward a DAVF, with retrograde drainage into the

radicular vein and subsequently to the ventral perimedullary venous plexus lon g ar-

row)

and then downward around the conus and upward to the dorsal venous plexus

short arrow).

Selective injection into the radicular artery

F )

showed converging

branches towards the DAVF arrowhead)draining into the ascending radicular vein

long arrow).

Embolization with a liquid mixture of glue

G )

demonstrates that the

embolic material has reached the proximal portion of the radicular vein

longarrow),

resulting in permanent obliteration and cure


24/24

87


In the past, excision of the dura at the site of fistula was proposed

(H ur th et al. 1978; Dav id 1982; Oldfield 1989; Sym on et al. 1984; Mo rgan

and M arsh 1989);however, this approach has for the most p art been aban-

do ned (Afshar et al. 1995).The results of surge ry are very muc h the sam e

as glue embolization. Of 55 patients re po rted o n by Sym on et al. (1984) (50

with SDAVFs),7

(13 )

deteriora ted afte r surgery. Symon ascribed this de-

terioration to excision of some of the coronary venous plexus of the spinal

cord in association with division of the radicular vein emptying into th e

me dullary venous system. Stripping the vein on th e do rsal surface of the

spinal cord m ust therefore be discouraged at all costs, as it is the wrong

type of opera tion a nd m ay lead to clinical worsening. In Symon's series, in

65 of the 31 severely disabled patients and in 80 of 15 mo derately dis-

abled patients, there was appreciable improvem ent of gait and sph incter

control. Similarly go od results were noted in five out of six patients re -

ported on by Oldfield (1989) and in seven of eight operated o n by Morgan

an d Marsh (1989) (one patient was not operated on by the author). A good

surgical response was also mo re recently note d by Westphal et al. (1999)

an d van Dijk et al. (2002). In patients w ith intracran ial sh unts dr ain ing

downward toward the spinal cord veins, interrup tion of the vein drainin g

the fistula will give similar good resu lts.

12.5.5

Postoperative Follow up

In the great majority of patients with SDAVFs who have undergone en-

dovascular or open surgery, some improvem ent or a rrest in progression

follows. In those with no imp rovement w ithin 4-6 weeks after trea tm ent ,

repeat MRI and angiographic investigation should be considered. MRI

may be able to show evidence of progressive venous throm bosis a s an ex-

trem ely rare unfavorable progression of previously successful treatm ent.

MRI at 4-8 weeks after treatm ent rarely shows imp rovem ent in signal

changes within the spinal cord, even in patients who respond favorably to

trea tm ent (Willinsky et al. 1995). Therefore, the absence of im provement

as shown on MRI does no t necessa rily reflect residual o r recu rren t DAVF,

as the MRI findings tend to lag behin d the clinical findings. On the other

ha nd, if MRI clearly shows the persistence of flow voids along th e sp inal

cord in a patient who did not respond to therapy, then repeat an giography

is indicated (Mascalchi et al. 2001). The repeat angiographic work-up

should sta rt with the injection of the anterior spinal artery to verify the

circulation time again. If prolon ged, the ipsilateral a nd co ntralateral arte-

rial pedicles at th e level of the DAVF as well as those abov e an d below tha t

level should be reevaluated. If no residual fistula is dem onstrated a search

should be m ade to exclude the occ urrenc e of a second fistula. Similarly, n

those patients showing initial improvement but subsequent cessation of

improvement or deterioration, reevaluation is mandatory, as recanaliza-

tion or developm ent of a second fistula, althoug h extremely rare, may be

found.

12 spinal dural arteriovenous fistulae

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