Development of contralateral symmetric (mirror) aneurysm after a trapping procedure. An 18-year observation.

An 18-year-old male medical student presented with subarachnoid hemorrhage. Other than stiffness of the neck, the neurological examination yielded normal findings. Bloody cerebrospinal fluid was obtained by lumbar puncture. Bilateral carotid arteriography revealed a right internal carotid artery aneurysm at the level of the posterior communicating artery. The angiogram of the left carotid artery was entirely normal. A right trapping procedure followed. The patient was asymptomatic for 4 years, when a repeat subarachnoid hemorrhage occurred. A new (mirror) aneurysm on the opposite (left) internal carotid artery was at this time demonstrated by repeat bilateral carotid arteriography. The newly developed aneurysm was successfully clipped. The patient has led a normal, useful life, with no recurrent episodes of subarachnoid hemorrhage in the next 18 years.