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Title: Spinal Dural Arteriovenous Fistulas


1
Spinal Dural Arteriovenous Fistulas
  • Terence Sasaki, M.D.
  • Tibor Becske, M.D.
  • Peter Kim Nelson, M.D.

2
Spinal Dural Arteriovenous Fistulas
  • Abstract
  • The most common of the spinal vascular
    malformation, the spinal dural arteriovenous
    fistula (SdAVF), is a rarely thought about cause
    of back pain and myelopathy. This devastating
    entity is often overlooked and the result can be
    permanent paraplegia with loss of sphincter
    control. Perhaps the most important factor in
    diagnosis is inclusion in ones etiologic
    considerations. In this review, we depict the
    history, dissect the anatomy, explain the
    pathogenesis, and discuss the treatment options
    of SdAVFs.
  • Keywords
  • AVF, AVM, dural arteriovenous fistulas,
    neurointerventional, neuroendovascular, spinal
    arteriovenous fistulas, spinal arteriovenous
    malformations, review

3
Anatomy of this Presentation
  • Review of Anatomy
  • Classification of the types of Spinal vascular
    malformations
  • SdAVFs
  • Epidemiology -- Diagnosis
  • Clinical Features -- Treatment
  • Pathophysiology
  • Conclusions

4
Basic Anatomy
  • The circulation of the spinal cord consists of
    the intrinsic and extrinsic systems.
  • The extrinsic or macrocirculation subsists of the
    radiculomedullary (ASA) and radiculopial (PSA)
    system fed by their respective medullary and pial
    branches of the radicular arteries.
  • A potential watershed exists between the adjacent
    medullary arteries.

Drawing from WE Krauss Vascular anatomy of the
spinal cord In Nsurg Clin N Am 10(1)9-15, 1999
Jan
5
Arterial Macrocirculation
  • The cervicothoracic region has the greatest
    variability in supply, the midthoracic has a
    single anterior medullary artery, and the
    thoracolumbar and sacral regions share the artery
    of Adamkiewicz (T9-L2).
  • At the medullocranial junction, the dorsal cord
    is subserved by extradural vessels.
  • Anterior spinal artery supplied by 7-8 anterior
    medullary arteries
  • Posterior spinal arteries supplied by posterior
    medullary (radiculopial) arteries

Drawing from WE Krauss Vascular anatomy of the
spinal cord In Nsurg Clin N Am 10(1)9-15, 1999
Jan
6
Arterial Microcirculation
  • The intrinsic or microcirculation consists of
    the central arteries off the ASA, the pial
    (coronal) plexi from the ASA PSA, and the
    radial branches which travel to deeper spinal
    cord structures.

Drawing from WE Krauss Vascular anatomy of the
spinal cord In Nsurg Clin N Am 10(1)9-15, 1999
Jan
7
Venous System
  • The venous drainage is accomplished by several
    systems. The anteromedian group of intrinsic
    veins drain the anterior columns, the grey and
    white commissures, and the medial anterior horns.

Drawing from WE Krauss Vascular anatomy of the
spinal cord In Nsurg Clin N Am 10(1)9-15, 1999
Jan
8
More Veins...
  • First traveling in the anterior sulcus as the
    central vein, it continues as the anteromedial
    spinal vein, then eventually as the anterior
    medullary vein entering the epidural plexus and
    terminating in the azygos/vena caval system.
  • The rest of the cord is drained by the radial
    veins into the anterior and posterior coronal
    plexi which also contribute to the medullary
    veins.

Drawing from BE Kendall and V Logue Spinal
Epidural Malformations Draining into Intrathecal
Veins. Neurorad 13, 181-189 (1977)
9
  • The medullary veins number two in the cervical,
    one each in the upper mid thoracic, two in the
    lower thoracic, and one at about the level of the
    third lumbar vertebral body.
  • Batsons (perivertebral) plexus is located in the
    region of the neuroforamen and are a conglomerate
    of the epidural plexus, medullary veins, and
    vertebral veins.
  • Rich anastomoses exist between the anterior and
    posterior plexi in the lower thoracic region.

Reference Kendall and Logue, Neurorad 13,
181-189 (1977)
10
  • The cranial dural layers separate at the region
    of the foramen magnum to become the spinal dura
    and the periosteal dura of the spinal canal
    separated by the epidural space.
  • Within the subarachnoid space a venous reticulum
    called the coronary plexus is normally separated
    from the epidural venous system, perhaps by
    valves.
  • Thus the dural and nerve root arteries do not
    normally communicate with the medullary veins
    the dura and extradural tissues have separate
    drainage pathways from the cord.

11
  • As elegantly described by Manelfe in 1972, the
    dura is supplied by the intraspinal division of
    each dorsospinal branch of the segmental artery
    at every level and from both sides.
  • Both supplying and running alongside nerve
    sleeves, they split to longitudinal and
    transverse anastomoses both ventrally and
    dorsally.

JC Watson EH Oldfield The Surg Management of
Spinal Dural Vascular Malform. In Neurosurg Clin
N Am 10(1)73-88, Jan 1999
12
Classification
  • Vascular malformations of the CNS have been
    classified by McCormick () and Russell
    Rubinstein () into four major pathologic types
    (a) AVM (b) cavernous angioma (c) capillary
    telangiectasia and (d) venous angioma.
  • Aside from these congenital (developmental)
    lesions, a distinct entity is the dural AVM.
  • The dural AVM (or fistula) represents an acquired
    vascular lesion, characterized by arteriovenous
    (AV) shunting involving vessels within the dural
    venous sinuses and coverings of the brain/spinal
    cord.
  • Various classification systems and eponyms for
    these lesions have been used over the years with
    resultant confusion and difficulty in comparing
    and evaluating the various subgroups.

13
Timetable of Spinal vascular history
Hebold 1885, Gaupp 1888 ? 1st description of spinal vascular malformations (angiomas)
Elsberg, 1914 ? 1st successful surgery
Foix-Alajouanine, 1926 ? subacute (angiodysgenetic) necrotizing myelopathy
Perthes, 1927 ? identified spinal AVM on myelogram
Michon, 1928 ? described the syndrome of spinal SAH
Wyburn and Mason, 1943 ? clinical features described
Djindjian et al, 1962 ? selective spinal angiography
Doppman and Di Chiro, 1965 ? focus on nidus
Doppman et al, 1968 ? endovascular treatment (embolization)
Yasargil Krayenbuhl, 1969 ? microsurgical technique
Kendall and Logue, 1977 ? distinction of dural and intradural AVM
Anson and Spetzler, 1992 ? current classification
14
Types of Spinal Vascular Malformations
  • Spinal dural arteriovenous fistula (SdAVF)
  • Spinal extradural (epidural or paravertebral)
    AV fistula
  • Spinal cord (or intramedullary) arteriovenous
    malformation (SCAVM)
  • Spinal cord (perimedullary) arteriovenous
    fistula (SCAVF)
  • Cavernous malformation (CM)

Modified after Anson and Spetzler 1992
Berenstein and Lasjaunias 1992.
15
  • Anson and Spetzler Type I vascular malformations
    are SdAVFs. They account for 60-80 of spinal
    vascular malformations.
  • Thought to be acquired lesions, spinal dural
    arteriovenous fistulas (SdAVF) are defined as
    small AVFs involving a dural branch of the
    radicular artery drained by a single radicular
    vein which then drains into the intradural
    perimedullary veins.

Drawing Rosenblum et al. J Nsurg 67195-802, 1987
16
SdAVFs
  • Unlike spinal CORD vascular malformations, they
    are NOT supplied by the anterior and posterior
    spinal arteries (ASA PSA).
  • Their shunts and draining veins are usually
    within the dura at the level of the nerve root
    foramen on the posterolateral aspect in the
    axilla of the exiting nerve root.

17
Perimedullary AV Fistula
  • Type IV or intradural perimedullary AVFs, which
    account for 10-15 of cases, are supplied by the
    radiculomedullary or radiculopial arteries.
  • These are further subdivided into three types
    depending on the size and number of feeders.
  • The intradural location of the shunt, the
    constant involvement of spinal cord arteries, and
    the lack of intervening nidus are
    angioarchitectural features that differentiate
    them from both SdAVFs as well as intramedullary
    AVMs.

Text reference Anson and Spetzler 1992 Drawing
Rosenblum et al. J Nsurg 67195-802, 1987
18
Intramedullary AVM
  • The rarest form, type II or intramedullary AVM,
    is found within the parenchyma or pia and
    believed to be congenital.
  • They can be glomus or juvenile in nature.
  • Type III stands for extensive AVM with vertebral
    or paraspinal involvement

Drawing Rosenblum et al. J Nsurg 67195-802, 1987
19
Comparison of SdAVF spinal cord arteriovenous
malformations (SCAVM)
Feature SDAVF SCAVM
Age gt4th decade 2nd-3rd decade
Symptom onset Slow progressive Acute
Male predominance Yes (marked) Minimal
Hemorrhage No Yes (frequent)
Bruit No 5-10
Origin Acquired Congenital
Site of nidus Dura, root sleeve Spinal cord
Medullary arterial involvement 10-20 100
Adapted from Muraszko and Oldfield
20
Epidemiology
  • Spinal vascular malformations make up
    approximately 3 to 16 of spinal mass lesions.
  • Of these at least 35 represent SdAVFs, although
    some estimates range as high as 80. SdAVF, the
    most common type of spinal AVM, affects patients
    late in adulthood typically during their middle
    ages with the mean age of onset of 55.
  • Males are the predominant victims, 4-91, and
    typically the SdAVF lesion is located in the
    thoracolumbar region.

21
Clinical Features
  • Patients initially present with back or sacral
    pain, leg numbness or weakness causing gait
    difficulty.
  • Often patients initially notice weakness then
    sensory problems with these progressing to overt
    paraplegia in 2-4 years.
  • The weakness can be from both upper as well as
    lower motor neuron dysfunction.

22
  • Patients can be wrought with paresthesias and
    spasms which may culminate in wasting and
    fasciculations
  • Both the sensory deficits and pain can result
    from cord and/or radicular involvement.
    Hyperesthesia may develop especially in the trunk
  • The sensory level is seldom above T10. Patients
    often complain that symptoms worsen with exercise
    or illness

23
  • When sphincter or sexual dysfunction occurs
    later, they rarely regress.
  • This underlines the importance of an early
    diagnosis. Rarely these may precede the other
    symptoms.
  • SdAVFs must be differentiated from MS, myopathy,
    cord compression whether intrinsic or extrinsic,
    motor neuron disease, infection (tropical spastic
    parapareis/HAM), or syringomyelia.

24
  • The chronic progressive course, which
    characterizes the clinical course in 80, can be
    occasionally interrupted by acute exacerbations.
  • Although episodic deterioration can occur, the
    step-wise progression of nidal hemorrhages seen
    with intramedullary lesions does not occur.
  • The absence of hemorrhage seen in other spinal
    AVMs is thought to be attributable to the
    location (no pial supply) and slow flow nature of
    the shunt. The chronicity of cord vascular
    congestion is thought to be another factor.

25
Foix-Alajouanine Syndrome
  • In 10-15, patients have an acute/subacute
    presentation of symptoms with rapid progression,
    sometimes termed the Foix-Alajouanine syndrome.
  • This entity is characterized by a subacute
    necrotizing myelopathy of venous thrombosis and
    resultant infarction.

26
Pathophysiology
  • Believed to be an acquired rete along dura, the
    SdAVF often begins at the axilla of a nerve root
    sleeve, dorsal to the nerve root.
  • The feeder of the fistula is a dural branch of
    the radicular division of an intercostal or
    lumbar artery.
  • Initially, it is a tiny, very slow flow shunt but
    with the buildup of pressure, flow reverses in
    the medullary veins in a centripetal fashion and
    thus the lesion drains intradurally.

27
  • Due to the limited capacitance, the
    arteriolization of the radicular vein causes the
    perimedullary veins to engorge resulting in a
    distended and stagnant venous plexus.
  • As hypertension develops in the venous system, it
    causes the intrinsic cord veins to become
    congested eventually slowing flow in the
    anterior spinal artery.

Note the enlarged venous structures surrounding
the cord.
28
  • This venous stasis results in decreased perfusion
    and resultant hypoxia of neural tissue.
  • Intramedullary vasodilation, coinciding with the
    loss of the autoregulatory reflexes, may also
    occur.
  • This further contributes to the cord edema,
    stagnation of blood flow, and the disruption of
    the blood-CNS barrier.
  • Cord edema results in upper motor neuron symptoms
    which progress to lower motor neuron symptoms
    once anterior horn cells are damaged by ischemia.

29
  • Regardless of the site of fistula, edema starts
    at the most dependent area of the cord (conus).
  • The result is a subacute ascending progression of
    symptoms including weakness.
  • There may be a discrepancy between the observed
    spinal level and the fistula level.
  • The cord edema commonly terminate at or below the
    level of the heart about T5. This is believed to
    be the result of venous return to the heart
    assisted by gravity above T5.
  • Myelomalacia can occur with longstanding lesions.

30
  • Mean arterial pressures can rise with exertion
    complicating cord perfusion further and resulting
    in claudication.
  • In the past, this mechanism was thought to be due
    to a steal phenomenon.
  • At times, local compression due to distended
    vasculature can result in nerve root or cord
    compression.
  • SdAVFs almost never bleed because of the slow
    flow dynamics described above.
  • Multiple lesions are uncommon.

31
  • A SdAVF differs from a cranial dural AVF because
    it drains directly into a subarachnoid vein
    without an intervening dural sinus.
  • Although cranial AVFs are thought to result from
    thrombosis triggering angiogenesis and subsequent
    shunting, this is likely not the mechanism which
    explains SdAVF pathogenesis. Preceding epidural
    lakes or varices are sometimes observed.

32
Diagnosis
  • CSF A mild to moderate protein elevation (up to
    500) with little cell elevation is seen in CSF
    analysis.
  • Myelogram
  • MRI
  • Angiogram

33
Myelogram
  • Myelogram displays serpentine or totuous filling
    defects or bag of worms appearance.
  • Because the posterior medullary veins are more
    abundant and the posterior longitudinal vein is
    generally larger, myelograms are more sensitive
    if performed in the supine position.

34
MRI Sagittal T2-weighted images
  • The MR often displays an expansile conus which
    may have nonspecific enhancement and is often
    mistaken for tumor, inflammation, or
    demyelination.
  • The profound superior extension of cord edema,
    which is visualized as T2 hyperintensity, as well
    as the multiple enhancing vessels, which produce
    a tortuous or studded appearance, are
    characteristic.
  • Chronic disease can present with an atrophic cord.

35
Seen here is a swollen cord with high intensity
signal on T2-weighted images indicative of edema.
Also seen are multiple dilated vascular channels
adjacent to the cord.
  • The dilated pial veins, often on the dorsal cord
    surface, may be seen best on T2-weighted images
    as areas of tortuous flow void adjacent to the
    high signal cerebrospinal fluid (CSF).

36
Angiography
  • When spinal angiography is performed, the entire
    neural axis should be systematically searched.
  • However, a scanning aortogram can often spot the
    feeder saving valuable time.
  • Barring this, each of the segmental arteries
    should be selectively catheterized in turn.
  • Bowel movement can be reduced with glucagon but
    should be used sparingly due to tachyphylaxis.
    Liberal use of apnea is suggested.
  • Be sure to include the internal iliac and the
    sacral arteries (median lateral) to exclude
    pelvic contribution.
  • The skull base branches of the vertebral and the
    carotid (internal external) arteries as well as
    the ascending cervical and the thyrocervical
    trunks also have been known to feed cephalad
    based SdAVFs.

37
  • Late arterial phase image of Rt T6 intercostal
    artery injection reveals a dural AVF
  • Note the tortuous and dilated perimedullary veins
    extending both cranially and caudally

38
  • Late venous images reveal the craniocaudal extent
    of venous congestion

39
  • Once the lesion has been located, it is important
    to identify the anterior and posterior spinal
    arteries.
  • If either of these arteries are communicating
    with the lesion or from the same pedicle,
    embolization is contraindicated due to the risk
    of infarction.
  • In 10 to 15 of cases, the SdAVF is fed by a
    radicular artery that also contributes the spinal
    cord supply via a radiculomedullary or
    radiculopial branch.

40
Stereoscopic views early to midarterial phase
  • By taking images at 6 degrees angles, the two
    images can be visually combined by slightly
    crossing the eyes.

41
Stereoscopic views late arterial phase
  • The resultant three dimensional image can help
    understand spatial relationships.

42
Treatment Endovascular
  • Because of recanalization risks and inadvertent
    migration, both coils and particles are not
    recommended for SdAVF embolization.
  • Relapse often occurs in 2-8 months.
  • In an attempt to isolate the draining vein and
    the perimedullary veins, typically the fistula
    and the distal 1-2 cm of the adjacent vein are
    filled with acrylate liquid glue.
  • Histoacryl (0.5 mL), otherwise known as
    N-butyl-2-cyanoacrylate (NBCA), and Lipiodol
    (1.2mL), an iodized oil to delay polymerizing
    time, are combined with a radioopaque substance
    such as tantalum powder.

43
Pre-treatment angiographic evaluation
  • Early arterial phase
  • Late arterial phase
  • Venous phase

44
Embolization with NBCA
  • Post Embolization
  • Microcatheterization
  • Pre Embolization

45
  • Endovascular treatment is technically not
    feasible in up to 40 of cases
  • Reasons include
  • -ASA/PSA contribution from the same pedicle
  • -failure of microcatheterization (tortuous
    anatomy dissection of arterial pedicle)
  • -failure of glue penetration across fistula .
  • If embolization has failed or cannot take place,
    a platinum coil can sometimes be used to
    fluoroscopically mark the feeding artery to
    facilitate subsequent surgery.
  • This risks worsening the hemodynamics of the
    lesion however if surgery is not performed soon.

46
Outcome
  • Clinical stabilization or improvement occurs in
    60-87 of endovascular cases with a complication
    rate ranging from 1.6-5.5.
  • The extent of recovery is dependent on the
    nature, severity and duration of symptoms before
    treatment.
  • Recurrence of symptoms may affect up to 40 of
    patients.
  • In these, collateralization of the incompletely
    embolized fistula or, rarely, true recanalization
    (?) can be the etiology.
  • Alternatively a new fistula or progressive venous
    thrombosis can account for the recurrence of
    symptoms. If this is the suspected cause,
    systemic anticoagulation should be initiated.

47
Treatment Surgical
  • Goal complete and permanent occlusion of the
    fistula.
  • This is accomplished by coagulating and dividing
    the intradural draining vein.
  • Exposure of the nerve root followed by
    coagulation and resection of the dura containing
    the fistula can also be performed. This may be
    necessary with fistulas that have epidural
    drainage in addition to the intradural one.

Drawing from Watson JC, Oldfield EH The surg
management of spinal dural vascular malform
Nsurg Clin N Am 101, January 1999
48
  • The surgical procedure is not technically
    challenging provided the surgeon understands the
    pathophysiology and has a good quality angiogram
    to refer to during the case.
  • Stripping of the dilated and tortuous venous
    stuctures is contraindicated (this used to be
    routine practice).

Microsurgical photograph Note the tortuous veins
on the dorsal surface of the dural sac.
49
Outcome
  • An improvement is seen in 70-95 with
    complications happening 0-16 of the cases.
  • The extent of recovery is dependent on the
    nature, severity and duration of symptoms before
    treatment.
  • Surgical mortality is close to 0.

50
Follow-up
  • Postoperative or postembolization MRI (3-6 mos
    post procedure) to confirm resolution of cord
    edema and disappearance of dilated vascular
    channels.
  • If symptoms recur, MRI followed by spinal
    angiography is indicated to assess for
    recanalization, venous thrombosis or de novo
    fistula formation.

51
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