Congenital absence of the cervical and petrous internal carotid artery with intercavernous anastomosis.

Congenital absence of an internal carotid artery is a rare anomaly. Less than 1 00 cases have been reported in the English literature. It is usually associated with collateral flow to the involved vascular territory, so neurologic deficits are few. However, this anomaly is also associated with a high occurrence of intracranial aneurysms. We report two cases of absent internal carotid artery with collateral supply of blood through an anastomotic vessel arising from the cavernous region of the contralateral internal carotid artery. Both cases presented because of complications of associated aneurysms.