Identical cerebral aneurysms in siblings: report of two families.

Two pairs of sisters with identical cerebral aneurysms are reported. In the first family, a sibship of three, the two female members presented with subarachnoid haemorrhages from identical, left internal carotid artery bifurcation aneurysms. The subarachnoid haemorrhage occurred in one of the sisters at the age of 20 and at the age of 50 in the other. The remaining healthy sibling, a 40-year-old male, underwent elective cerebral angiography, which was normal. The other sibship, two 48-year-old female identical twins, had identical right middle cerebral artery aneurysms. The first twin became symptomatic after subarachnoid haemorrhage. The aneurysm in her identical twin was identified by screening angiography. There were no verified subarachnoid haemorrhages among the parents and grandparents in either family. No systemic anomalies were identified and collagen type 3 deficiencies were excluded. The identical location of these familial aneurysms, particularly in view of the relatively rare location in the first family, suggests that local factors in the developing vascular tree may play a role in the pathogenesis of saccular aneurysms in addition to systemic anomalies affecting the general structure of cerebral vascular walls.