False localization of rupture by computed tomography in bilateral internal carotid artery aneurysms

BACKGROUND Focal clot on computed tomographic (CT) scan is one of the most reliable clues in determining the site of rupture in patients with multiple intracranial aneurysms. However, unusual presentation of clot may cause false localization of the ruptured aneurysm in bilateral aneurysms, particularly when they are located near the midline. METHODS We describe two cases of bilateral internal carotid artery (ICA) aneurysms presenting contralateral distribution of clot on CT scan. RESULTS Misjudgment of rupture site by the CT scan resulted in clipping of the wrong aneurysm in one patient. Disastrous rebleeding occurred before the second operation for the ruptured one. In the other patient, the rupture site was assumed correctly despite contralateral situation of clot on CT, and both aneurysms were treated in one operative session. CONCLUSIONS Adhesion and obliteration of the subarachnoid cisterns from previous hemorrhage will deviate the direction of hemorrhage and present contralateral clot on CT scan in bilateral aneurysms located near the midline as ICA aneurysms. Medial direction of rupture may obscure accurate localization of rupture side in such aneurysms.