Vascular Diseases of the Nervous System: Spinal Cord Vascular Disease

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Chapter 51E Vascular Diseases of the Nervous System

Spinal Cord Vascular Disease

David S. Geldmacher

The spinal cord is subject to many of the same vascular diseases that involve the brain, but its anatomy and embryology render it susceptible to some syndromes that do not have intracranial counterparts.

Vascular Anatomy of the Spinal Cord

The embryonic arterial supply to the spinal cord derives from intradural vessels that enter at each spinal level and divide to follow the dorsal and ventral roots. The ventral radicular branches join along the midline to form the anterior spinal artery. Irregular anastomoses among the dorsal roots, as they enter the cord on each side, form paired posterior spinal arteries. The anterior and posterior spinal arteries constitute longitudinal arterial plexuses. Circumflex vessels (arteria vasocorona) connect the anterior and posterior arterial systems in a pial plexus around the lateral margins of the cord (Fig. 51E.1).

Fig. 51E.1 Arterial supply to the spinal cord and nerve roots at the level of a medullary radicular artery.

(Adapted from Henson, R.A., Parsons, M., 1967. Ischaemic lesions of the spinal cord: an illustrated review. Q J Med 36, 205-222.)

During development, a few radicular arteries become dominant and provide most of the flow to the spinal cord through the anterior spinal artery. These are variably known as medullary or radiculomedullary vessels. Unfortunately, the terms radicular, medullary, and radiculomedullary are often used interchangeably in the literature. Five to eight of these vessels typically persist in adults. The largest and most frequently identified of the anterior vessels is the arteria radicularis magna or great artery of Adamkiewicz, which courses along one of the lower thoracic or upper lumbar anterior roots to join the anterior spinal artery. It provides a major portion of the blood flow to the lower thoracic cord and the lumbar enlargement. The sacral cord, conus medullaris, and cauda equina are supplied by small lower segmental radicular arteries. In general, a larger number of smaller vessels serve the posterior spinal artery. The cervical and upper thoracic spinal cord is richly vascularized by a plexus arising from branches of the ascending cervical and vertebral arteries (Fig. 51E.2).

Fig. 51E.2 Relationship of typical anterior medulloradicular arteries and spinal cord segments. Lower thoracic levels are at greatest risk for ischemia during hypoperfusion.

The main blood supply to spinal gray matter, as well as to anterior and lateral funiculi, is derived from anterior sulcal arteries. These arise from the anterior spinal artery in the midline and course into the ventral median fissure. Each anterior sulcal artery distributes blood to only the left or right half of the spinal cord. The greatest distance between sulcal arteries is in the thoracic segments; the vascularity is proportional to the numbers of neurons located throughout the cord at that level. The dorsal columns and extreme dorsal horns (approximately one-third of the cord cross-section) are supplied by penetrating branches from the posterior spinal arteries. The superficial white matter also receives blood flow via the circumflex anastomotic vessels. This arrangement leads to a clinically relevant border zone between the territories of the sulcal and superficial arterial distributions. As a result, many spinal cord infarctions do not follow the conventional boundaries between anterior and posterior arterial distributions (Ishizawa et al., 2005).

The venous system of the spinal cord parallels the arterial supply. A group of radial veins flows outward to the surface of the cord, ending in a coronal plexus, and deep parenchymal veins empty into central sulcal veins in the median fissure. Unlike the arteries, however, each parenchymal vein drains both the right and left sides of the cord. There are few venous anastomoses within the substance of the cord, but sulcal veins often have intersegmental anastomoses. The anterior median spinal vein, which lies external to its corresponding artery, is filled from the sulcal veins. As with the other spinal veins, the median spinal vein is more irregular than the corresponding artery and may be doubled at some levels. Extramedullary venous channels are also prominent along the dorsal cord, and the dominant vessel is usually the posterior median spinal vein. There is no corresponding artery in the midline. Eight to twelve major anterior radiculomedullary veins arise from the anterior median spinal vein. They are joined by anterolateral anastomoses from the coronal venous plexus at the nerve roots before passing through the dura. There is typically a large vein that drains the levels of the lumbar enlargement (vena radicularis magna). Posterior radicular veins are present throughout but are particularly prominent in the cervical region.

Venous blood from the entire cord runs into the epidural and paravertebral venous plexuses, forming a large valveless system from sacrum to occiput, known as the vertebral venous plexus or Batson plexus. The absence of valves to resist retrograde flow in this continuous venous network may be a factor in the pathogenesis of some spinal cord vascular disease.

Spinal Cord Ischemia

Paraplegia complicating aortic surgery was recognized as early as 1825, though it was not attributed to spinal cord ischemia until the 1880s. By the early 20th century, cardiac embolism, atheromatous disease, and decompression sickness were also described as causes of paraplegia attributable to spinal cord ischemia. The actual prevalence of spinal cord infarction is unknown but is generally cited as representing 1% to 2% of all central neurovascular events and 5% to 8% of all acute myelopathies. The clinical presentation of spinal cord syndromes is presented in more detail in Chapter 24.

Presentation and Initial Course

Weakness (100%), sensory loss (89%), back pain at onset (82%), and urinary complaints requiring catheterization (75%) were the most common symptoms of cord ischemia at the time of presentation in a prospectively collected series (Masson et al., 2004). In retrospective series, the same major symptoms are observed, though with minor differences in observed frequency (Kumral et al., 2010; Nedeltchev et al., 2004; Novy et al., 2006). The most common location to be affected is the mid- to low thoracic spine. Lower cervical lesions are less common, and upper thoracic spinal infarcts are rare. Quadriparesis is present in only 20% to 25% of all cases of spinal infarction.

Pain and sensory changes occur first in most cases, followed by weakness within minutes or hours. Over 80% of the back pain with spinal infarction follows a radicular pattern (Novy et al., 2006), but in cases of acute aortic disease, pain may have a more visceral character. Maximum motor disability is observed within 12 hours of onset in a majority of patients, with a trend toward longer intervals when dysfunction was less severe. Urinary retention is typical in the acute phase, but involuntary voiding or defecation may be associated with the onset of the ischemic insult.

Examination Findings

Weakness most commonly affects both legs. Examination typically reveals flaccid paresis accompanied by diminished superficial and tendon reflexes below the level of the lesion. Preservation of strength and reflexes suggests posterior spinal artery territory infarction. Sensory changes, when present, nearly always affect spinothalamic modalities. Isolated proprioceptive loss is rare.

Investigations

Magnetic resonance imaging (MRI) is the diagnostic procedure of choice for detecting spinal cord ischemia, although the results can be normal in up to one-third of patients (Novy et al., 2006). In the acute phase of spinal cord infarction, high diffusion-weighted imaging signal is noted and matches with low apparent diffusion coefficient signal (Thurnher and Bammer, 2006). Pencil-shaped hyperintense signal on T2-weighted images initially appear within 2 hours to several days, and may be accompanied by gadolinium enhancement (Weidauer et al., 2002). Abnormal signal and contrast enhancement may demonstrate a double-dot (“owl’s eyes”) pattern in the region of the anterior horns, an H-shaped pattern involving the central gray matter, or a more diffuse pattern involving both gray and white matter (Fig. 51E.3). The diffuse pattern may be difficult to distinguish from venous infarction. When cord infarction results from compromise of a segmental artery, branches supplying the ipsilateral half of the vertebral body may also be affected. Vertebral body infarct is best detected on sagittal T2-weighted images, usually appearing as a triangular area of increased signal near the end-plate and/or deep medullary portion of the vertebral body.

Fig. 51E.3 Subacute arterial infarction of the conus medullaris. A 69-year-old man had sudden onset of paraparesis and loss of bowel and bladder function 8 days prior to the magnetic resonance (MR) study. A, T2-weighted, fast-spin echo image shows focal enlargement and hyperintense signal within the conus medullaris. B, Postcontrast T1-weighted axial image (T12 level) shows abnormal enhancement in an H-shaped pattern involving the central gray matter.

(From Bowen, B.C., Saraf-Lavi, E., 2005. Magnetic resonance imaging and magnetic resonance angiography of spinal vascular lesions. In: Latchaw, R.E., Kucharczyk, J., Moseley, M.E. (Eds.), Imaging of the Nervous System. Diagnostic and Therapeutic Applications, vol 2. Mosby, Philadelphia, pp. 1707-1722, with permission.)

Other laboratory and radiographic studies are not diagnostic in noncompressive spinal cord ischemia. Myelography is usually normal. Cerebrospinal fluid (CSF) protein was elevated in 44% of one series, but pleocytosis was not observed (Novy et al., 2006).

The exact cause of spinal ischemia often remains occult and could not be discerned in up to half of prospective and retrospective series (Masson et al., 2004; Novy et al., 2006).