What predisposes the watershed zone in the spine to infarction?

Spinal Cord Watershed Zone Vulnerability to Infarction

The watershed zones in the spine are predisposed to infarction primarily due to their location at the distal boundaries of arterial territories where perfusion pressure is lowest, combined with the unique vascular anatomy that creates areas dependent on collateral flow from adjacent vascular territories.

Anatomic Factors Creating Vulnerability

Vascular Territory Junctions

• Watershed zones exist at the junction between major arterial territories where blood supply from adjacent vessels meets, creating regions with the most tenuous perfusion 1, 2.
• The spinal cord has both longitudinal watershed zones (between rostral and caudal arterial contributors) and transverse watershed zones (between anterior and posterior spinal artery territories) 3, 4.

Posterior Lumbosacral Watershed Zone

• A particularly vulnerable area exists at the dorsal aspect of the conus medullaris, where the posterior spinal artery territory meets the anterior spinal artery territory 1.
• This zone is at increased risk because of the caudocranial direction of flow within the most caudal segment of the posterior spinal arterial network, which functionally depends on the anterior spinal artery 1.
• The periconal arterial anastomotic circle configuration in the conus medullaris region creates a specific watershed territory with unique vulnerability 1.

Hemodynamic Factors

Decreased Perfusion Pressure

• Decreased cerebral perfusion in distal regions of vascular territories makes these areas vulnerable to ischemia, as the perfusion pressure is lowest at the boundaries between arterial territories 5, 2.
• Watershed zones are susceptible to global hypoperfusion states including prolonged hypotension, cardiac arrest, blood loss during surgery, and thoracoabdominal procedures 3, 4.

Dependence on Collateral Flow

• These regions rely heavily on collateral circulation from adjacent arterial territories, making them vulnerable when any contributing vessel is compromised 1.
• Intersegmental artery compromise through compression mechanisms (diaphragmatic crus syndrome, disk herniation) can precipitate watershed infarction by decreasing spinal cord perfusion 1.

Predisposing Clinical Conditions

Atherosclerotic Disease

• Preexisting atherosclerotic disease significantly increases vulnerability, as it reduces baseline perfusion reserve in watershed territories 3, 4.
• Patients with extensive intraluminal thrombus and bilateral spinal artery occlusion are at particularly high risk for widespread watershed lesions during hypotensive episodes 4.

Surgical and Hypotensive Events

• Thoracoabdominal surgery creates risk through both direct vascular manipulation and perioperative hypotension 3.
• Postoperative blood loss leading to prolonged hypotension is a recognized precipitant of spinal cord watershed infarction 3, 4.

Clinical Pitfalls to Avoid

• Do not overlook compression mechanisms (disk herniation, diaphragmatic crus) that can compromise radiculomedullary arteries supplying watershed zones 1.
• Recognize that watershed infarction can manifest as central necrosis with peripheral sparing in the transverse axis and central lesions with rostral and caudal sparing in the longitudinal axis 4.
• Be aware that the posterior thoracolumbar watershed zone represents an area at increased risk, particularly with partial flow impairment from arterial compression 1.