[Non-traumatic dissecting aneurysms on the intracranial internal carotid artery: report of three cases].

Subarachnoid hemorrhage (SAH) due to non-traumatic dissecting aneurysms is uncommon. Most of such cases are reported to occur in the posterior circulation. We encountered three cases of non-traumatic dissecting aneurysms on the intracranial internal carotid artery. Two cases developing SAH from the dissecting aneurysms were surgically treated by such means as proximal ligation and trapping. Two cases, which were treated surgically during the acute phase, showed poor surgical outcome, because a large cerebral infarction took place during the course of vasospasm. Trapping of the ICA or the contralateral ICA with the dissecting aneurysm failed to keep enough blood supply despite hypervolemic hypertensive therapy. Operative results seemed to depend on the collateral circulation during vasospasm, so appropriate bypass surgery was recommended in cases of dissecting aneurysm on the ICA manifesting SAH. Furthermore, the mechanism of initiation of a dissecting aneurysm on the intracranial carotid artery was discussed from the biorheological aspect.