[A case of persistent primitive proatlantal intersegmental artery (proatlantal artery I) with aneurysm--a case report].

A 70-year-old woman was admitted to our hospital with attack of SAH. On admission, she was semi-comatose with no other neurological deficit. Left carotid angiography revealed an aneurysm of the anterior communicating artery and a large abnormal vessel connecting the left external carotid artery and the left vertebral artery. This large anastomotic vessel was thought to be primitive proatlantal intersegmental artery (proatlantal artery I). Right carotid angiography revealed a coiling of the right internal carotid artery and hypoplasia of the right A1 portion. Left retrograde brachial angiography revealed aplasia of the left vertebral artery. After admission her consciousness gradually improved but 17 days after admission she died of rerupture of the aneurysm. Autopsied brain showed that the left vertebral artery, namely proatlantal artery, was almost as large as the basilar artery and its macroscopical appearance was similar to other arteries. It was also obvious that the right vertebral artery was hypoplastic. As the rate of combination of the persistent artery with the intracranial aneurysm is relatively high, the authors think that some congenital factor may affect the occurrence of intracranial aneurysms.