The specimen consists of the left half of the brain. The third ventricle is distorted as is the adjacent
brain tissue by an aneurysm some 4 cm across occupied by laminated clot. The optic chiasma can
be seen distorted beneath it. The aneurysm would appear to be arising from the basilar artery.
This man presented at the age of 42 with an aneurysm of the basilar artery which could
not be clipped because of the atheromatous condition of the vessel. Accordingly both vertebral
arteries were ligated but the aneurysm continued to expand until five years later an attempt was
made to deal with it under hypothermia and with circulatory arrest. His initial postoperative
progress was good but he subsequently died some months later.