The watershed (boundary zone) between the anterior cerebral artery (ACA) and middle cerebral artery (MCA) territories is vulnerable in systemic hypotension. A bilateral watershed infarction in the ACA–MCA boundary zone characteristically causes:

• A Dense hemiplegia and hemisensory loss — identical to MCA territory infarction
• B Locked-in syndrome — unable to move all limbs but preserved consciousness via eye blinking
• C Man-in-a-barrel syndrome — bilateral proximal arm weakness with spared face and leg function (transcortical motor aphasia if dominant) ✓
• D Quadrantanopia — loss of upper visual field in both eyes

Explanation

The ACA–MCA watershed zone corresponds to the region of cortex representing the proximal upper limb (shoulder and arm) — in the parasagittal cortex between the hand area (MCA) and the leg area (ACA). Bilateral watershed infarction from systemic hypoperfusion preferentially affects the proximal arm representation, causing weakness of both shoulders and proximal arms while the face and legs are relatively spared — the 'man-in-a-barrel' syndrome. If the dominant hemisphere watershed is affected, transcortical motor aphasia (aphasia with intact repetition) occurs. Locked-in syndrome results from bilateral ventral pontine infarction.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.