Ruptured middle cerebral artery aneurysm with intramural myxoid degeneration in a child.

A 9-year-old girl presented with a subarachnoid hemorrhage. Cerebral angiography showed a saccular aneurysm arising from the horizontal portion of the right middle cerebral artery. The aneurysm was successfully clipped, and the dome of the aneurysm was excised for pathological study. Histological examination of the aneurysm wall showed that the entire thickness of the wall showed an increased myxoid degeneration. No dissection was present. Most intracranial aneurysms in childhood are believed to be of the saccular type similar to that in adults, but the pathogenesis of the aneurysm formation remains controversial. Myxoid degeneration may cause intracranial saccular aneurysm with eventual rupture, even in the absence of dissection. This is the first case reported of a ruptured saccular aneurysm caused by myxoid degeneration in a child. The possible pathophysiology is discussed.