Background The existence of spinal cord watershed territories was suggested in the 1950s. Segmental infarcts within the junctional territories of adjacent radiculomedullary contributors and isolated spinal gray matter ischemia constitute two well-recognized types of watershed injury. This report describes the existence of another watershed territory related to the particular configuration of the spinal vasculature in the region of the conus medullaris.

Methods The anatomical bases underlying the concept of a posterior lumbosacral watershed zone are demonstrated with angiographic images obtained in a 16-year-old child. The clinical importance of this watershed zone is illustrated with MRI and angiographic data of three patients with a conus medullaris infarction.

Results In all three cases of spinal ischemia an intersegmental artery providing a significant radiculomedullary contribution for the lower cord was compromised by a compressive mechanism responsible for decreased spinal cord perfusion (diaphragmatic crus syndrome in two cases, disk herniation in one). The ischemic injury, located at the junction of the anterior and posterior spinal artery territories along the dorsal aspect of the conus medullaris, was consistent with a watershed mechanism. This zone is at risk because of the caudocranial direction of flow within the most caudal segment of the posterior spinal arterial network which, from a functional standpoint, depends on the anterior spinal artery.

Conclusions The posterior thoracolumbar watershed zone of the spinal cord represents an area at increased risk of ischemic injury, particularly in the context of partial flow impairment related to arterial compression mechanisms.