Spinal Cord Infarction

Excerpt

Comprehension of the anatomy of the spinal cord and its respective functions is paramount when diagnosing and managing spinal cord infarction (SCI). The spinal cord has 31 pairs of dorsal and ventral roots emanating from the cervical (n=8), thoracic (n=12), lumbar (n=5), and coccygeal (n=1) segments. The anterior two-thirds of the spinal cord contains motor and spinothalamic modalities, and the posterior one-third houses the proprioceptive tracts. The lateral region of the spinal cord contains the lateral corticospinal, rubrospinal, and medullary reticulospinal tracts.

The spinal cord receives its vascular support from one anterior spinal artery (ASA) and two posterior spinal arteries (PSA) that span the length of the cord longitudinally. They originate from the vertebral arteries at the level of the craniocervical junction, they anastomose via the vasocorona and transverse radicular branches forming the pial plexus, then give rise to small perforating branches that enter the spinal cord and supply the different tracts. (Figure 1)

The ASA gives rise to the sulcocommissural artery, which is also responsible for providing blood supply to the anterior part of the spinal cord. The PSA can also originate from posterior inferior cerebellar arteries (PICA); it also relies on posterior radicular arteries (originating from a vertebral artery) for vascular supply. Five to eight of the radicular arteries assume a dominant role in supplying the ASA; one of the thoracolumbar arteries emanating from T9 to T12 is said to assume that role in 90% of people and provides vascular perfusion to the lower thoracic and lumbar spinal cord in addition to the conus medullaris. It is known as the artery of Adamkiewicz.

The spinal cord bears a high level of collateral circulation, thus decreasing its susceptibility to vascular injury; there is also a degree of variation in circulatory support among different individuals. Perfusion of the anterior two-thirds of the spinal cord and the anterior portion of the posterior column occurs via the anterior spinal artery (ASA), and the posterior one-third region of the spinal cord receives its supply from the two posterior spinal arteries (PSA). The PSA supplies the posterior columns, posterior dorsal horns, portions of the corticospinal and spinothalamic tracts. There are speculations regarding a potential watershed zone between the regions supplied by the ASA and PSA involving the anterior dorsal horns and part of the corticospinal and spinothalamic tracts; however, there has been no clear evidence yet published. The lower thoracic spinal cord carries a higher risk of infarction due to its hypovascularity and a lesser degree of collateral circulation.

The anterior spinal and medial posterior veins are responsible for providing venous drainage to the spinal cord; together, they form a venous network surrounding the cord, similar to the arterial system. Radicular veins are present in high quantity and channel through to the intervertebral and paravertebral plex, which direct blood flow to the azygos and pelvic venous systems. The spinal venous network is valveless, thus rendering it susceptible to infections.