[Relationship between the afferent artery and the site of neck of anterior communicating artery aneurysm, and hemodynamics in the anterior part of the circle of Willis (author's transl)].

Of 346 patients with direct intracranial surgery for an aneurysm of anterior communicating artery that we have experienced from June 1961 to September 1975, 213 patients having sufficient data were selected to study a relationship between hypoplasia of the A1 of the anterior communicating artery, and sites of an afferent artery and a neck of an aneurysm. 1. Ninety seven of 182 patients who had had the bilateral angiography before surgery had hypoplasia of the right A1, 90 of which (92%) had an afferent artery of an aneurysm only in the left A1. All 29 patients with hypoplasia of the left A1 had an afferent artery of an aneurysm only in the right A1. An afferent artery was limited to the dominant A1 in about 95% of them. 2. Angiography revealed that of 204 patients in whom the neck of an aneurysm in the anterior communicating artery was confirmed, 140 patients had hypoplasia of a unilateral A1. The neck of an aneurysm was located at the bifurcation of the dominant A1 and the anterior communicating artery in 48 of the 140 patient (34.3%), at the bifurcation of the non-dominant A1 and the anterior communicating artery in 14 patients (10.0%), and in the anterior communicating artery itself in 78 patients (55.7%). Cerebral angiography revealed that the neck of an aneurysm was more than 3 times greater at the bifurcation of the dominant A1 and the anterior communicating artery than at the bifurcation of the non-dominant A1 and the anterior communicating artery. 3. The above findings suggest that hemodynamics in the anterior part of the circle of Willis may participate in the initiation, growth, and rupture of an aneurysm of the anterior communicating artery.