Mechanisms and clinical features of posterior border-zone infarcts.

BACKGROUND

Previous studies link posterior border-zone cerebral infarcts between the middle cerebral artery (MCA) and the posterior cerebral artery (PCA) to hemodynamic causes, not embolism.

OBJECTIVE

To study the cause of these infarcts.

METHODS

We studied 21 patients (unilateral = 18, bilateral = 3) with acute, symptomatic posterior border-zone infarcts shown on CT or MRI to clarify stroke mechanisms. Patients were identified by review of CT and MRI logs and medical records during a 35-month period. An embolic mechanism was assigned when a source of embolism from either the heart, aorta, or parent large artery was present in the absence of intrinsic MCA or PCA disease. A hemodynamic mechanism was assigned when systemic hypotension was present.

RESULTS

Among patients with unilateral lesions, 10 were embolic (7 cardiac, 3 carotid), 7 were unknown, and one patient had vasospasm from a ruptured aneurysm. Visual field abnormalities predominated over motor, sensory, and language abnormalities. All patients with bilateral posterior border-zone lesions had perioperative hypotension. Prolonged lethargy, bilateral limb weakness, and cortical blindness were common.

CONCLUSIONS

Embolism, either cardiac or from the parent carotid artery, is the predominant stroke mechanism in unilateral posterior border-zone infarcts, not distal field perfusion failure. Bilateral posterior border-zone infarcts have a distinctive clinical presentation and are caused by systemic hypotension. Variability of irrigation of the major arteries, passage of emboli to border-zone areas, and decreased clearance of emboli in these areas explain the findings in the patients with unilateral lesions.