A thrombosed giant aneurysm of the internal carotid artery with brain stem displacement.

A giant aneurysm with a maximum diameter of 5.2 cm arising from the right internal carotid artery grew to occupy the interpenduncular cistern and displaced the upper brain stem. Most of the lumen of the aneurysm was occluded by a thrombus and its real dimension in situ was visualized by CT scan. The neck of the aneurysm was successfully clipped but removal of the aneurysm was not feasible. Following surgery, clinical signs and symptoms gradually improved and subsequent decrease in size of the thrombosed aneurysm was documented by serial CT scans.