[A case of absence of the left internal carotid artery associated with aneurysm of the anterior communicating artery].

A 67-year-old female was admitted to our hospital because of unconsciousness after severe headache on April 7, 1986. On admission, the patient was semicomatose with anisocoria and absence of light reflex. Computed tomography showed subarachnoidal hemorrhage with intraventricular clots. Right carotid angiogram revealed that the left anterior cerebral artery was filled from the right side through the anterior communicating artery and a saccular aneurysm in anterior communicating artery. On left-side carotid angiogram, neither the left internal carotid artery nor the intracranial arteries were visualized. She died on the 15th hospital day. Complete absence of the left internal carotid artery and hypoplasia of the left A1 portion were verified at autopsy. Sixteen cases of agenesis of the unilateral internal carotid artery have been associated with cerebral aneurysms in the literature. Absence of internal carotid artery was discussed in relation to aneurysm formation.