Spinal Vascular Malformations Sohail Bajammal February 2, 2009

Acknowledgement Dr. Aleksa Cenic

Outline Embryology Anatomy Classification Clinical presentation Treatment

Embryology of the Spinal Vascular Network 4 stages Congenital theory of AVMs: 20% of patients with intradural AVMs have other associated congenital vascular malformations: intracranial AVMs, cerebral aneurysm, vascular agenesis, hemangioblastoma, Rendu-Osler-Weber syndrome, Klippel-Trenaunay-Weber syndrome Present in younger patients Distributed throughout the entire spinal axis

Stage I “Primitive Segmental Stage” Week 2-3 gestation 31 pairs of segmental vessels originate from paired dorsal aortas  grow toward the neural tube along the developing nerve roots Segmental vessels divide into ventral & dorsal branches and form capillary networks on the ventrolateral surface of the neural tube These networks develop into paired primitive ventral arterial tracts, the precursors of the anterior spinal artery

Stage II “Initial Stage” Week 3-6 gestation Development of the dorsal arterial anastomosis Longitudinal venous channels develop on both ventral and dorsal spinal cord surfaces These channels expand and give rise to interconnected capillary network AVM theoretically happens during this stage

Stage III “Transitional Stage” 6th week – 4th month gestation Formation of the adult pattern of vascular supply The primitive ventral longitudinal arterial tracts fuse and the number of segmental arteries is reduced By 10 weeks, adult patterns are present

Stage IV “Terminal Stage” After 4th month Maturation and increased tortuosity of the major spinal cord vessels

Adult Anatomy

Arterial Anatomy Anterior spinal artery: arises from the fusion of a contribution from each of the vertebral arteries supplies the ventral 2/3 of the cord narrows as it descends but reinforced by blood vessels at some segmental levels Paired posterior spinal arteries: run the length of the spine supply the posterior 1/3 of the cord

Arterial Anatomy At each segmental level: a dorsal ramus of the segmental artery enters the intervertebral foramen and gives rise to 3 branches: Dural branch: to dura Radicular branch: to nerve root Medullary branch: Augments the flow to the anterior spinal artery During the 3rd stage of fetal development, most of the medullary branches involute  distal portion of the cord relatively ischemic Somewhere between T8 & L2, especially on the left: the medullary branch does not involute and becomes the artery of Adamkiewicz

Venous Anatomy Coronal venous plexus: Epidural venous plexus: A plexus on the cord surface Formed by coalescence and anastomosis of radial veins Epidural venous plexus: At segmental levels, medullary veins leave the coronal plexus and exit the intervertebral foramen to join the epidural plexus The plexus communicates with the venous sinuses of the cranial dura It drains into the ascending lumbar veins and the azygous venous system

Spinal Vascular Malformations Terminology Definition: abnormalities of the arteries or veins surrounding the spinal column, spinal cord, and nerve roots AV fistula (AVF): direct communication between artery & vein AV malformations (AVMs): multiple complex communications Nidus: the core of an AVM that appears angiographically and anatomically as a conglomeration of vessels because of the superimposition of arteries and veins.

Spetzler et al. Modified classification of spinal cord vascular lesions. J Neurosurg (Spine 2) 2002.

Incidence Rare cause of neurologic dysfunction 5% of all intraspinal pathology Occur throughout the spine Affect any age group, majority: 30-50 Better diagnosis and management with improved techniques of spinal angiography, MRI, MRA and endovascular surgery O`Toole and McCormick. Chapter 83: Vascular Malformations of the Spinal Cord. Rothman-Simeone The Spine. 5th Edition

Clinical Presentation Haemorrhage Myelopathy Radiculopathy Back pain

Pathophysiology of Symptoms Depends on the type of the AVM High-flow: Ischemia Hemorrhage Slow-flow: Venous congestion Mechanical compression of the spinal cord and roots

Classification Many exist Most common: 4 types based on the location and angioarchitecture Anatomical: intradural vs extradural Presence or absence of AV shunts Recent: Spetzler 2002

4 Types Type I: Dural AV Fistula Type II: Glomus AVMs Type III: Juvenile AVMs Type IV: Intradural AV Fistula

Type I (Dural AV Fistula) The most common type 60% of spinal AVF/AVM Single AV connection within the dura of the nerve root sheath Results in dilated arterialized coronal venous plexus

Type I Figure 83-1 Anteroposterior view of right L1 selective angiography demonstrates the typical fistula (arrow) of a type I AVF and the characteristic intradural medullary draining vein that extends on the dorsal surface of the spinal cord over many rostral segments.

Type 1 Intraoperative photograph of a type I AVF shows enlarged coiled vein on dorsal spinal surface.

Pathophysiology of Type 1 Slow-flow  Intradural venous hypertension  progressive spinal cord ischemia Exercise (elevated intraspinal venous pressure)  reversible ischemic symptoms Venous hypertension may be exacerbated by structural changes in the veins Venous thrombosis  acute exacerbation

Clinical Presentation Type 1 Mean age: 50yr Men 4 times more common Majority: thoracic and thoracolumbar Symptoms: insidious back and leg pain, mild sensorimotor dysfunction (like spinal stenosis) Signs: mixed UMNL and LMNL and patchy sensory loss.

Natural History of Type 1 Inevitable progression of symptoms Episodes of acute worsening e.g., Foix-Alajouanine syndrome If untreated: wheelchair dependence within 6mo to 3 years after symptom onset Preoperative neurologic status is the most important predictor of post-treatment outcomes. Median time from symptom onset to diagnosis: 15 to 23 months.

Type II (Glomus AVMs) Analogous to intracranial AVMs Tightly packed nidus of dysmorphic arteries and veins in direct communication w/o capillary bed; over a short segment of the spinal cord The nidus may be completely or partially intramedullary Usually at the cervicothoracic junction

Selective spinal angiography reveals type II AVM of the cervical spinal cord supplied by a branch of the anterior spinal artery (arrow). B, Sagittal MRI demonstrates intramedullary location of the lesion (arrow).

Pathophysiology of Type II Vascular steal mechanism: High-flow lesion; AVM nidus acts as a low-resistance sump siphoning blood away from the surrounding normal spinal cord Dysmorphic vessels susceptible to hemorrhage Mass effect: myelopathy or radiculopathy

Clinical Presentation of Type II Childhood or adult years Acute presentation from subarachnoid or intramedullary hemorrhage is most common Acute onset of severe neck or back pain “coup de poignard” approximates the level of AVM: typically the first symptom of AVM hemorrhage

Type III (Juvenile AVMs) Arise in single or multiple adjacent somites  thus intradural and extradural, may involve soft tissue and bone in addition to the cord Diffuse shunts with normal spinal cord existing between loops of abnormal vessels No distinct nidus Metameric: tissue derived from the entire somite

Type IV (Intradural AVF) Direct connection between an intradural artery and vein in the subarachnoid space without a definable nidus Usually ventral, involves the anterior spinal artery Sub classified: small, medium, large

Pathophysiology of Type III & IV High-flow lesions Vascular steal/ischemia Hemorrhage Mass effect

Type V Type III lesions outside the spinal cord and dural (i.e., not truly metameric)

Diagnosis MRI and MR angiography (MRA): useful for the initial screening of AVMs. Permit more targeted selective angiography Selective spinal angiography: gold standard for definitive diagnosis and characterization

Treatment Goal: total obliteration or excision of the abnormal shunt If only partially reduce the shunt or address proximal feeders only  recurrence

General Considerations of Surgical Treatment Majority of AVMs are dorsal or dorsolateral  standard posterior laminectomy of appropriate number of levels Neuromonitoring: SSEPs & MEPs Wide laminectomy Dural opening with preservation of arachnoid

General Considerations of Endovascular Treatment Continues to evolve Advances in catheter technology, image resolution and embolization materials Neuromonitoring and pharmacologic intra-arterial provocative testing (amobarbital and lidocaine) Either primary or adjunctive role depending on the type of AVMs & expertise Procedure of choice for type III Type I & IV: attempts of embolization, if failed  surgery. Some authors prefer surgery as first line Type II: surgery remains the gold standard

Type I

Treatment of Type 1 Historically, stripping of the long dorsal vein  poor outcomes b/c removal of normal cord venous drainage Now, excision of the dural fistula Two-level hemilaminectomy and partial medial facetectomy to expose the dural root sleeve and foramen Paramedian longitudinal dural incision: exposes the intradural nerve root and initial segment of draining vein Several mm of the feeding radicular artery and intradural draining vein, cauterized, divided and excised along with a small window of dura on the root sleeve.

Outcomes of Type 1 Treatment Neurologic improvement or stabilization in 70 to 99%. Motor and gait disturbances improve to a greater degree than sensory or sacral deficits Surgery produces 98% fistula obliteration rate, endovascular embolization produces 25 to 66% obliteration rate. O`Toole and McCormick. Chapter 83: Vascular Malformations of the Spinal Cord. Rothman-Simeone The Spine. 5th Edition

Type II

Treatment of Type II Preoperative endovascular embolization to shrink the size Surgical excision: Interruption of the feeding arteries first If mainly intramedullary, midline myelotomy

Type III

Treatment of Type III The most difficult to treat They penetrate the spinal cord Do not have well-defined margins (intramedullary, intradural-extramedullary, extradural) over many spinal segments Generally unresectable. Palliative treatment with endovascular embolization, and/or surgery

Type IV

Treatment of Type IV Depends on the size and complexity Small: surgical ligation is definitive Posterior (or posterolateral) or anterior approach Usually needs spinal instrumentation Medium and large: endovascular embolization preferred as primary treatment or preopeative adjunct

Thanks

Credits Images from: Spetzler et al O`Toole and McCormick Oldfield