Complete middle cerebral artery block without brain infarction.

We report a patient with progressive supranuclear palsy and incidentally detected the absence of right middle cerebral artery (MCA) without any old or acute infarct in its territory. The magnetic resonance angiography and computed tomography angiography failed to detect any significant collateral circulation. We discuss the embryogenesis of brain circulation and offer a possible explanation for the nonvisualization of the right MCA in our patient.