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A 62 year-old man with developed an upper GI bleed complicated by severe hypotension. Several days after successful surgical repair of a bleeding gastric ulcer, it was noticed that he had significant weakness of the right shoulder and hip girdle muscles.
MRI axial flair images: Note the linear area of infarction between the distributions of the middle and anterior cerebral arteries on the left. The area in between two vascular territories is known as a watershed. Watershed infarcts occur following reduced perfusion pressure, as often occurs during cardiac events or severe bleeding. The watershed territory between the MCA and ACA corresponds to the shoulder and hip girdle muscles on the motor homunculus, leading to the characteristic clinical deficits (patients' weakness is often referred to the man in the barrel distribution). When a watershed infarction is seen on one side, this usually occurs due to hemodynamic narrowing of a proximal artery (e.g., in this case, the carotid artery) with or without superimposed hypotension.
The Electronic Curriculum is copyrighted 1998, Case Western Reserve University School of Medicine.