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bosis or because of a hypercoagulable state [6].

It has been suggested that SDAVF is primarily a

venous disease, often presenting with progres-

sive and ascending myelopathy and/or radicu-

lopathy [8, 9]. SDAVF is a potentially curable

cause and thus should be treated aggressively;

microsurgery and endovascular embolization are

the treatment choices [10]. Currently, with the

progress in SDAVF treatment, an updated review

is still necessary. Additionally, we provide edu-

cational images and cases in this review to

increase the reading interest. These images and

cases are from our hospital, and there are no

8.2 Natural History andCurrent

Diagnosed State

8.2.1 Natural History

In general, SDAVF has a poor natural history

[11]. Spontaneous regression is uncommon [12].

As described by Aminoff and Logue, if left

untreated, severe locomotor disability may

develop in nearly 20% of patients within 6months

of the onset of functional impairment in the legs;

50% of untreated patients are severely disabled,

and nearly 10% are able to walk independently

after 3 years [13]. SDAVF is often a slow pro-

gressive myelopathy, and a sudden onset of

symptoms is rare [4, 14]. Valsalva-like maneu-

vers can increase venous pressure and compro-

mise venous drainage of SDAVF, and these

maneuvers may also change the natural history

when there is rapid deterioration of the clinical

course [15].

Steroid administration can change the natural

history, and acute neurological deterioration in

patients with SDAVF receiving steroids has been

reported, even after successful obliteration of the

stula. This is because steroids produce hydro-

static retention, hypervolemia, and secondary

venous hypertension, which may lead to worsen-

ing of spinal cord edema [16–18]. Therefore,

steroids should be avoided in patients with

SDAVFs.

8.2.2 Diagnosed State

The initial symptoms of SDAVF can be nonspe-

cic, nonlocalizing, and gradual. Therefore, mis-

diagnoses are frequent and are attributed to aging,

stress, or exercise [3, 19, 20]. A diagnostic delay

may range from 1 to 2years, at which time 78%

of patients have severe lower limb weakness and

19% are wheelchair bound [21–23]. Currently, in

China, SDAVF is also an underdiagnosed disease

[24]. In Zhang etal.’s report, the diagnostic time

was 14.7 months from symptom onset [25].

Therefore, SDAVFs should be considered in all

patients with paraparesis, sensory decits, or

bowel/bladder dysfunction [26].

In addition, a major factor that contributes to a

misdiagnosis or a delayed diagnosis of SDAVF is

false-negative spinal angiographic imaging nd-

ings due to the stulas having limited shunting

owing to the relatively low venous hypertension

and technical difculty of the procedure [27].

Furthermore, SDAVFs can originate far from the

areas of visible pathological features seen on the

initial MR image or CT scan. The failure to per-

form angiographic evaluations at every spinal

level can lead to false-negative results [27].

8.3 Anatomy

andAngioarchitecture

8.3.1 Feeding andDraining Vessels

oftheNormal Spinal Cord

The spinal artery from the intersegmental artery

supplies the spinal cord, dura, and adjacent struc-

tures. The spinal artery gives off the radicular

artery, which supplies the spinal nerve root, the

radiculomeningeal branch (dural artery) of the

spinal artery supplies the dura, and the radiculo-

medullary artery of the spinal artery supplies the

spinal cord via the anterior spinal artery and

paired posterior spinal arteries [28].

Many arteries can give off spinal arteries,

including the vertebral artery, deep cervical

artery, ascending cervical artery, intercostal

artery, and lumbar and lateral sacral arteries

8 Current Status oftheTreatment forSpinal Dural Arteriovenous Fistulas

https://t.me/med1917

abc

Fig. 8.2 Overview of intersegmental arteries. (a) Aorta

angiography showing that intersegmental arteries may

arise from the aorta, vertebral artery, thyrocervical trunk,

and costocervical trunk. (b and c) Descending aorta angi-

ographies clearly showing the thoracic and lumbar (b) and

lumbar and sacral (c) arteries

(Fig.8.2) [24]. The venous drainage of the spinal

cord is collected by the anterior and posterior

longitudinal spinal veins linked together into

radicular veins and then via transdural emissaries

into intervertebral, longitudinal efferent, and

other level-specic venous channels [29, 30].

8.3.2 Angioarchitecture ofSDAVF

Approximately 80% of SDAVFs are found along

the lower thoracic cord surface between the levels

of T5 and L2 [19, 31, 32]. Low cervical DAVFs

(below C2 and above T1) are rare (Fig. 8.3) [9].

Most lesions are solitary, double, or multiple and

may be present in 0.5–4% of SDAVFs [33–36].

SDAVFs are often located in the dura of the dorsal

nerve root sleeve and/or adjacent dura at the inter-

vertebral foramen [3, 37]. However, in the conus/

lumbar regions, SDAVFs are not always the dor-

sal types [38, 39]. SDAVFs are often supplied by

adjacent segmental radicular arteries that are not

at the same level of the stula point, and the feed-

ing artery may be single but also uncommonly

can be multiple [24, 32].

In SDAVFs, the feeding artery splits into mul-

tiple vessels on the outer dural surface and

crosses the dura to the inner dural surface; these

vessels gather into a single arterialized draining

vein, which appears to be the caput medusae [26,

38, 40–42]. Therefore, more arterial blood ow is

delivered into the perimedullary vein in a retro-

grade manner.

Because the normal local radicular venous

drainage in SDAVF is often missing, stenosed,

or occluded, the blood has to ow over a long

distance along the dorsal perimedullary veins,

upward, downward, or both to arrive at the out-

ow into the epidural network, depending on

the patent intradural-to-epidural venous con-

nections and the pressure in the epidural space

[16, 24, 43, 44]. An insufcient venous outlet

plays a signicant role in the development and/

or persistence of SDAVFs [38]. SDAVF may

remain silent if the radicular venous drainage is

patent, especially for cervical lesions with

abundant collateral venous pathways [45].

However, when the venous drainage system is

inadequate to cope with the blood volume, pro-

gressive myelopathy will develop, resulting in

decreased tissue perfusion with edema and pro-

gressive loss of cord function from the venous

medullary congestion and increased pressure

(Fig.8.4) [14].

J. Yu

https://t.me/med1917

Fig. 8.3 Cervical

SDAVF treated by

microsurgery. (a) MR

T2WI showing an

intradural mass of

vessels (arrow) on the

dorsal surface of the

spinal cord. (b)

Angiography of the left

subclavian artery

showing an SDAVF

(arrow) supplied by the

thyrocervical trunk. (c)

Preoperative

angiography of the left

subclavian artery with

the patient in the prone

position, and the SDAVF

(arrow) is shown. (d)

Intraoperative image

showing an intradural

arterialized draining

vein (arrow) attached to

the inner dura. (e)

Intraoperative image

showing that the

arterialized draining

vein was clipped

temporarily. (f) After

clipping the arterialized

draining vein,

intraoperative

angiography showed

that the SDAVF was

completely occluded,

and the arrow indicates

the temporary clip.

Abbreviations: C7

seventh cervical

vertebra, L left, SDAVF

spinal dural

arteriovenous stula

8 Current Status oftheTreatment forSpinal Dural Arteriovenous Fistulas

https://t.me/med1917

e f

Fig. 8.4 Lumber

SDAVF treated by

microsurgery. (a) MR

T2WI showing dilated

vessels (arrows) on the

ventral and dorsal

surfaces of the spinal

cord and edema of the

spinal cord (asterisks).

(b) Preoperative

angiography of the

lumbar artery with the

patient in the prone

position showing the

SDAVF (arrow) between

the L2 and L3 vertebral

levels. The arrowheads

indicate the draining

vein, and the asterisks

indicate the anterior

spinal artery (artery of

Adamkiewicz). (c–e)

Intraoperative images

showing an intradural

arterialized draining

vein (arrow in c)

attached to the inner

dura, an arterialized

draining vein (arrow in

d) that is clipped

temporarily, and an

arterialized draining

vein (arrow in f) that

was cut. (f)

Postoperative

angiography showing

complete occlusion of

the SDAVF and

preservation of the

anterior spinal artery

(arrow). Abbreviations:

L left, L2 second lumbar

vertebra, L3 third

lumbar vertebra, SDAVF

spinal dural

arteriovenous stula

J. Yu

https://t.me/med1917

8.3.3 Classication ofSDAVF

Similar to intracranial DAVFs, SDAVFs can be

classied according to the Cognard subtypes: type

I, anterograde outow into the spinoradicular

(dural) vein or extradural venous plexus; type II,

retrograde outow into the extradural venous

plexus and pial venous plexus; and type III, retro-

grade outow into the pial venous plexus only [46].

8.4 Therapeutic Goal

andOptions

Based on the poor natural history, the treatment of

SDAVF is mandatory and aims at the interruption

of the venous side of the SDAVF and restoration

of the normal venous drainage of the spinal cord

[19, 26]. Even for asymptomatic SDAVF, treat-

ment should be offered [45, 47]. If the patient

refuses treatment, aspirin should be recommended

to reduce the risk of venous thrombosis to increase

the pressure of the spinal cord venous drainage

[43]. Surgical and endovascular interventions can

be used to treat SDAVFs [48]. For type II SDAVFs,

when both intra- and extradural venous drainage

are present, complete surgical excision or emboli-

zation of all the intra- and extradural venous

drainage is recommended [44, 49].

Microsurgery appears to be an efcient

method in terms of the clinical effect, radical-

ity, and lower recurrence (Fig. 8.4) [5, 32,

50–52]. In recent years, advances in endovascu-

lar techniques have greatly improved the ability

to treat a majority of SDAVF patients, espe-

cially for those patients with a reduced physical

condition (Fig.8.5) [53, 54]. The increased use

of endovascular embolization has led to many

recurrent SDAVFs [55]. For SDAVFs in which

endovascular embolization does not obtain a

cure or recurs, microsurgery can be recom-

mended [56–58]. Endovascular embolization

increases the degree of surgical complexity

because of the dissection and the identication

of vessels and tissues that are lled with

embolic material.

In addition, when SDAVF harbors a common

segmental artery supplying both the stula and

anterior spinal artery (especially for the artery

of Adamkiewicz) (Fig.8.4) or posterior spinal

artery, which can be seen in 14% of SDAVFs,

endovascular embolization should not be

attempted due to the possibility of developing a

dangerous anastomosis to the radiculomedul-

lary arteries, which will result in embolization

risks of spinal cord infarction. In these

instances, microsurgery can be recommended

[3, 19, 26, 38, 59].

8 Current Status oftheTreatment forSpinal Dural Arteriovenous Fistulas

https://t.me/med1917

a b

c d

Fig. 8.5 Thoracic

SDAVF treated by

endovascular

embolization. (a)

Descending aorta

angiography showing an

SDAVF (arrow) at the

T4 vertebral level. (b

and c

) Three-

dimensional (b) and

two-dimensional (c)

angiographies of the

intercostal artery

showing the stula point

(arrows) and draining

vein (arrowheads). (d)

Unsubtracted

angiography showing

that the stula (arrow)

had been penetrated by

Onyx into the proximal

draining vein

(arrowhead). (e)

Six-month follow-up

angiography of the

intercostal artery

showing complete

embolization of the

SDAVF without

recanalization. (f)

Vertebral artery

angiography showing an

associated epidural

cervical arteriovenous

stula (arrow).

Abbreviations: T4 fourth

thoracic vertebra,

SDAVF spinal dural

arteriovenous stula.

Note: The patient was a

weak old woman with a

reduced physical

condition

J. Yu

https://t.me/med1917

8.5 Microsurgery Technique

Microsurgery can be performed via posterior

laminectomy or hemilaminectomy [3, 46]. A

major challenge is determining the accurate pre-

operative location of SDAVF.Intraoperative DSA

can help to conrm the center of the surgical

approach to reduce the region of surgical explo-

sion (Fig.8.6) [55]. After dura opening, the intra-

vertebral foramen region should be sufciently

explored. The stula is typically located in a dor-

sal arterialized vein and in a nerve root sleeve

[60]. Then, the arterialized vein close to the dura

can be coagulated and divided (Figs.8.3 and 8.4)

[41]. It is of utmost importance to preserve the

artery of Adamkiewicz; it can share a common

trunk with the feeding artery of the SDAVF.At

this time, simple surgical interruption of the

draining vein is a good choice (Fig.8.4) [61].

In addition, it is crucial to avoid inadvertent

venous sacrice without disconnection of the s-

tula, which can lead to catastrophic consequences

[62]. For microsurgery of SDAVF, intraoperative

identication of the stula and conrmation of its

obliteration are important. Intraoperative DSA is

the best choice when a temporary clip can be

applied on the arterialized vein before coagula-

tion and division (Fig.8.3) [63]. In addition, uo-

rescein and indocyanine green arteriography or

microvascular Doppler can provide real-time

information about the precise location of SDAVFs

[55, 64–67].

c d

Fig. 8.6 Preoperative

location of thoracic

SDAVF. (a) Descending

aorta angiography

showing that no SDAVF

can be found, which

indicated the importance

of superselective

angiography. (b) Right

intercostal artery

angiography showing an

SDAVF (arrow). (c)

Unsubtracted

preoperative

angiography of the right

intercostal artery with

the patient in the prone

position showing the

stula between the T6

and T7 vertebral levels

at the junction (arrow)

of horizontal and

vertical lead bars

(asterisks). (d)

Postoperative

angiography showing

complete occlusion of

the

SDAVF.Abbreviations:

R right, SDAVF spinal

dural arteriovenous

stula, T6 sixth thoracic

vertebra, T7 seventh

thoracic vertebra

8 Current Status oftheTreatment forSpinal Dural Arteriovenous Fistulas

https://t.me/med1917

8.6 Endovascular Technique

Currently, the liquid embolic agents for endovas-

cular embolization for SDAVFs mainly include

N-butyl-2-cyanoacrylate (NBCA) and Onyx

(Medtronic, Irvine, CA, USA) [19, 37]. For

embolization of SDAVF, occlusion of the proxi-

mal draining vein plays an essential role (Fig.8.5)

[68]. Only interruption of the feeding artery with

proximal occlusion alone is not considered effec-

tive, although it results in a transient improve-

ment of symptoms [57].

Successful endovascular embolization

requires a microcatheter to obtain the wedged

position; at this time, the vessel lumen of the s-

tula feeder is blocked with a microcatheter tip,

and the blood ow is arrested, which allows bet-

ter penetration of the liquid embolic agent into

the stula and the proximal draining vein [69].

However, the wedged position cannot be obtained

in all cases, especially in SDAVFs with tortuous

feeders, and the microcatheter may fail to access

the site of the stula [26].

To improve the curative rate of endovascular

embolization, if the feeding artery has a large

diameter, the dual-lumen balloon and pressure

cooker technique called the induced-wedge

technique is helpful when it is not possible to

navigate a ow-directed microcatheter to close

the stulous zone [42, 69, 70]. A dual-lumen

Scepter C balloon (MicroVention, Tustin, USA)

can increase the venous penetration of liquid

embolic agents, and the balloon can block the

reux and favor anterograde migration of liquid

embolic agents into the stula [71]. In the pres-

sure cooker technique, after the rst microcath-

eter is placed into the stula, a second

microcatheter is used and is substituted for the

balloon by performing coiling of the feeding

artery to block the reux, which can also favor

the penetration of liquid embolic agents into the

stula [70].

8.7 Complications

andRecurrence

8.7.1 Complications

In a meta-analysis by Goyal etal., the complica-

tion rates of microsurgery and endovascular

embolization were 7.7% and 6.9%, respectively

[51]. Microsurgical complications were associ-

ated with wounds, such as infections and hemato-

mas of the surgical eld and CSF leaks [38].

Complications with endovascular embolization

were technique-related adverse events, such as

microcatheter ruptures, spinal cord infarction,

and other unintended ischemic complications due

to nontarget embolization [70, 72].

In addition, after closure of the vein by micro-

surgery and embolization, in theory, there is a

risk of retrograde venous thrombosis, which

could involve veins that participate in the drain-

age of the normal spinal cord [49, 73]. Therefore,

the patient is well hydrated and begins a low-dose

heparinization and aspirin regimen for prophy-

laxis and/or treatment of venous thromboembo-

lism during the immediate postoperative period

[73].

8.7.2 Recurrence

Postoperative recurrence or recanalization was

dened as the presence of persistent arteriove-

nous shunting or SDAVF at the time of the rst

and/or last angiographic follow-up compared

with the initial posttreatment angiogram, and

there was clinical deterioration or lack of

improvement following the intervention [55, 60,

72]. In a meta-analysis by Goyal etal., endovas-

cular embolization was associated with 19.8% of

patients having initial residue and 11.2% of

patients having late recurrence [51]. The main

reason is that SDAVFs are often fed by long

J. Yu

https://t.me/med1917

arcades and are supplemented by adjacent seg-

ments, sometimes with a seemingly complete

angiographic occlusion, and recanalization is

seen with the opening of new venous drainage

[38, 74].

In addition, in some cases of SDAVF, embolic

material deposits along the inner walls of drain-

ing veins, giving the false radiological impres-

sion of complete occlusion while an inner lumen

persists, and the persistent shunt often leads to

progressive recruitment and growth of secondary

arterial feeders [55, 75].

8.8 Prognosis

Microsurgical treatment and endovascular embo-

lization are associated with cure rates of nearly

100% and 25–89.5%, respectively [1, 9, 51, 56,

73, 74]. An anatomical cure of SDAVF can be

obtained by either microsurgery or embolization,

but the functional outcome is not always satisfac-

tory [49]. The spinal cord neurological function

can be assessed and graded according to the

Aminoff-Logue disability (ALD) scale and mod-

ied Rankin scale (mRS) [13, 74, 76]. In

Durnford et al.’s report of 57 patients with

SAVDF who underwent occlusion, the ALD

scores improved during the 5-year follow-up by a

median of 1 point, and 49% of the patients had a

1-point improvement in their mRS score [74]. In

the Japanese Registry of Neuroendovascular

Therapy 2 and 3 with 172 SDAVFs, postoperative

neurological improvement was achieved in

48.3% of the patients, and an mRS score of 0–2

on postoperative day 30 was achieved in 60.5%

of the patients [31].

In general, postoperatively, two-thirds of

patients have relief and resolution of symptoms

[14]. In these patients, the motor symptoms

improved more than the sensory disorders, pain,

or sphincter impairment [2, 3, 22, 77]. These

improvements are preserved over an average of

3 years of follow-up [26]. For the treatment of

SDAVFs, one-third of patients had no satisfying

recovery. How to predict the treatment outcome

of SDAVF is still a matter of dispute [78]. It

remains difcult to predict whether patients will

obtain clinical improvement or whether the treat-

ment will simply halt the progression of symp-

toms [20].

It seems that the neurological function status

before treatment and the anatomical location of

the stula can predict the postoperative outcome.

SDAVFs associated with severe neurological def-

icits at presentation tend to have worse posttreat-

ment functional outcomes [22]. Preoperative

(1day before treatment) ALD was the strongest

predictor of clinical improvement [78]. The lower

thoracic area was associated with a favorable out-

come, and the middle thoracic and lumbar areas

were associated with lower rates of improvement

[3, 20, 23, 79]. In lumbosacral SDAVF, the post-

operative micturition function recovery was

superior to thoracic SDAVF [80].

It is worth noting that postoperatively, approx-

imately 50% of patients suffered late clinical

deterioration after temporary recovery, especially

at the 72-month follow-up [78]. The main mecha-

nism underlying this phenomenon is a gradual

and irreversible decline in spinal function related

to hemodynamic modications induced by

SDAVF and to the persistence of a state of de-

ciency of spinal venous drainage (Fig.8.7) [81].

8 Current Status oftheTreatment forSpinal Dural Arteriovenous Fistulas

https://t.me/med1917

a b

c d

Fig. 8.7 Postoperative

state of venous drain age

of SDAVF. (a)

Preoperative

angiography of the left

lumbar artery showing

an SDAVF (arrow)

between the L1 and L2

vertebral levels. (b)

Preoperative MR T2WI

showing dilated vessels

(arrows) on the ventral

and dorsal surfaces of

the spinal cord and

edema of the spinal cord

(asterisks). (c)

Postoperative

angiography showing

the SDAVF and the

complete occlusion of

the SDAVF. (d)

Postoperative 8-month

follow-up MR T2WI

showing the regression

of spinal cord edema;

however, dilated vessels

(arrows) on the dorsal

surfaces of the spinal

cord still exist.

Abbreviations: L left, L1

rst lumbar vertebra, L2

second lumbar vertebra,

SDAVF spinal dural

arteriovenous stula

8.9 Summary

SDAVF is a rare disabling disease and is often

misdiagnosed. SDAVF has a poor natural history.

The angioarchitecture of the SDAVF is complex.

SDAVF is a potentially curable disease and thus

should be treated aggressively. Surgical and endo-

vascular interventions can be used. Microsurgery

appeared to be an efcient method in terms of the

clinical effect, radicality, and lower recurrence in

comparison with endovascular embolization.

However, endovascular embolization is becoming

popular due to the advances in the techniques.

Although there are complications and unsatisfac-

tory prognoses, SDAVF treatments are still rec-

ommended; moreover, the sooner the treatment is

implemented, the better the prognosis.

Acknowledgments The author thanks Dr. Yunbao Guo

for providing the educational images in Figs.8.3 and 8.4

and Xuan Chen for providing the educational images in

Fig. 8.5 (other images are provided by the author). The

author conrms that the permission from the colleagues

who provided the case images to include these in a com-

mercial publication.

J. Yu

https://t.me/med1917

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