Spinal Vascular Malformations

Spinal Vascular Anatomy

To understand the pathophysiology and treatment of spinal cord vascular malformations requires knowledge of spinal vascular anatomy . The spinal cord receives arterial blood supply through two distinct arterial systems, a single anterior spinal artery and paired posterior spinal arteries ( Fig. 100.1 ). The anterior spinal artery is formed by the convergence of two branches of the distal vertebral arteries that join anterior to the cervicomedullary junction and descend in the anterior median sulcus. The anterior spinal artery receives segmental blood supply from radiculomedullary arteries arising from the vertebral arteries, costocervical or thyrocervical trunks, and intercostal, lumbar, and sacral arteries. Typically, two large radiculomedullary branches supplement the anterior spinal artery. A large radicular feeder usually arises at the C5 or C6 level from the vertebral or ascending cervical artery and is called the artery of cervical enlargement. The largest of the radiculomedullary branches is known as the artery of Adamkiewicz, which usually arises from a lower intercostal artery and enters the spinal canal on the left side at a variable level between T8 and L4. The artery of Adamkiewicz ascends anterolateral to the cord and takes a hairpin turn to descend to the conus medullaris (CM). As radiculomedullary arteries enter the dura at the nerve root sleeve, small branches supply the adjacent dura.

The paired posterior spinal arteries run longitudinally along the dorsolateral aspect of the spinal cord behind the dorsal nerve roots. Similar to the anterior spinal artery, the posterior spinal arteries receive radiculomedullary feeders from the vertebral, intercostal, and lumbar arteries. The anterior spinal artery supplies the anterior two-thirds of the spinal cord, and the posterior spinal arteries supply the posterior columns and portions of the lateral columns. The posterior spinal arteries join with the distal anterior spinal artery at the CM to form the cruciate anastomosis.

The venous drainage of the spinal cord is through small radial veins that course through the spinal cord parenchyma into the coronal venous plexus along the surface of the spinal cord. The convergence of the coronal venous plexus on the surface of the spinal cord forms the medullary veins that exit at the nerve root sleeves.

Classification and Epidemiology

Most spinal vascular malformations can be classified into one of four types that differ in etiology, anatomy, pathophysiology, radiological appearance, and treatment. Additionally, cavernous malformations occur in the spinal cord.

The type I spinal vascular malformation is most common and consists of a single arteriovenous fistula imbedded within the dura around the proximal nerve root sleeve and adjacent spinal dura. The feeding artery is a dural branch off the radiculomedullary ramus of an intercostal or lumbar segmental artery. From the dural nidus, outflow of the fistula is intradural through the medullary vein into the dorsal venous plexus along the surface of the spinal cord ( Fig. 100.2 top left). These lesions typically occur in the lower thoracic region in males, most commonly in the fifth to sixth decades of life.

Less commonly, type I spinal AVMs have two or more arterial feeders that enter at separate segmental levels. The additional dural branches travel within the dura to the fistula nidus where they converge to communicate with the efferent vein. Type I AVMs are subdivided into types Ia and Ib based on the presence of one or multiple arterial feeders, respectively .

Type II spinal cord AVMs, or glomus AVMs, are intramedullary vascular malformations that have a true, compact nidus within the parenchyma of the spinal cord ( Fig. 100.2 top right). Type II AVMs are less common than type I AVMs, occur most frequently in the cervical spine with equal sex incidence, and present in a younger population. The nidus is often fed by the anterior spinal artery, but may have multiple feeders.

Type III spinal AVMs, also known as juvenile AVMs, are quite rare, occur with equal sex incidence and usually present in adolescents and young adults. These complex, extensive lesions have both intramedullary and extramedullary components and often extend into extraspinal tissues as well ( Fig. 100.2 bottom left).

Type IV spinal AVMs, or perimedullary arteriovenous fistulae, occur more commonly in males and are intermediate in incidence between the more common type I and less common types II and III spinal AVMs . The intradural extramedullary fistula drains directly into an enlarged venous outflow of varying size. They present through a broader age range than other spinal AVMs. These lesions are most commonly supplied by the anterior spinal artery and are located anterior to the spinal cord, most often at the CM ( Fig. 100.2 bottom right).

Spetzler et al. previously published a modified classification of spinal vascular abnormalities that includes separate categories for aneurysms and neoplasms of a vascular nature in addition to the four types of malformations described . This expanded classification scheme includes lesions outside the narrow focus of this chapter; however, the authors describe CM AVMs as a subtype of spinal vascular anomaly distinct from the types I–IV as aforementioned. While anecdotal, our single center experience has lead us to believe that the CM AVM deserves consideration as a unique entity with idiosyncratic pathophysiology and treatment considerations.

Pathophysiology, Hemodynamics, and Natural History