This young patient presented obtunded after a prolonged period of hypotension as a result of a drug overdose.

Watershed infracts occur at the border between territories, typically as a result of prolonged hypotension. Lesions are usually unilateral and occur on the side of severe carotid stenosis. The best known pattern is that of cortical infarction between middle cerebral artery, anterior cerebral artery and posterior cerebral artery. The other pattern, less well publicised is the so called internal watershed (this case), between “medullary arteries arising from the superficial pial plexus and deep penetrating arteries arising from the basal cerebral arteries” (1). The tissue at risk in this pattern is the white matter tracts of the corona radiata, and centrum semiovale. When internal infarction is confluent, then clinical outcome is poor, with only 3 of 6 patients achieved independence in one study (1).

For more images (CT and MRI) of the same patient, please visit here.

C. F. Bladin et al “Clinical Features, Pathogenesis, and Computed Tomographic Characteristics of Internal Watershed Infarction” Stroke 1993;24;1925-1932
Credit: Dr Frank Gaillard