Aqueductal blood clot as a cause of acute hydrocephalus in subarachnoid hemorrhage.

We describe two patients with acute hydrocephalus, in whom CT scans did not show intraventricular hemorrhage unequivocally. Midline sagittal MR imaging revealed a blood clot plugging the aqueduct. MR imaging is useful for detecting sub-acute clots within the aqueduct and for differentiating them from other entities.