Segmental medullary artery

Segmental medullary arteries (Radiculomedullary arteries, RMAs) are a small subset of radicular arteries that, rather than terminating at the spinal nerve root, continue medially to reach and reinforce the longitudinal spinal arteries primarily the anterior spinal artery (ASA) and, to a lesser extent, the posterior spinal arteries (PSAs).

Origin and course

Segmental arteries arise from major regional vessels depending on the spinal level: the vertebral arteries, ascending cervical arteries, deep cervical arteries, intercostal arteries (from the aorta), lumbar arteries, and sacral arteries. At each vertebral level, a segmental artery gives rise to a radicular artery that enters the intervertebral foramen to supply the spinal nerve root and dura. Although there are 31 pairs of radicular arteries, only 6 to 10 of these extend beyond the nerve root to become true radiculomedullary arteries that reach and reconstitute the anterior spinal artery.

The artery of Adamkiewicz

The largest and most clinically significant segmental medullary artery is the great radicular artery (Artery of Adamkiewicz; Arteria radicularis magna; Great anterior radiculomedullary artery). It most commonly arises from a left-sided intercostal or lumbar artery between T8 and L2, with a left-sided origin in approximately 81% of individuals. It is the dominant feeder of the ASA in the lower thoracic and lumbar spinal cord. A cadaveric study of 25 specimens found that 32% had additional supporting radiculomedullary arteries beyond the artery of Adamkiewicz, and 8% had two arteries of Adamkiewicz.

The artery of von Haller

A recently characterized constant anterior radiculomedullary artery at the upper thoracic level (T3-T7), most frequently originating at T5, has been termed the artery of von Haller. Angiographic data show that 86% of patients have at least one ASA contributor between T3 and T7, undermining the classic concept of a thoracic watershed zone..