[Saccular aneurysm arising in the non-branching segment of the distal anterior cerebral artery with stalk-like narrow neck: a case report].

An aneurysm arising in the distal anterior cerebral artery (DACA) is relatively rare. Among them, those in the non-branching segment are seldom reported so far. The authors present the case of an 87-year-old woman who developed intracerebral hemorrhage and acute hydrocephalus due to rupture of an aneurysm arising in the non-branching site of DACA. External ventricular drainage followed by aneurysm clipping by bifrontal craniotomy was performed as treatment. Microscopic observations revealed that the aneurysm was saccular-shaped, located at the non-branching site of the A3 portion of the anterior cerebral artery, and had significant atherosclerosis neither on its parent artery nor neck. Histopathological examinations of the aneurysm wall denied traumatic aneurysm or mycotic aneurysm, and showed partial disruption of the internal elastic lamina, suggesting a difference from common aneurysms arising at arterial branchings. Profound knowledge of this type of aneurysms would be useful in dealing with them at surgery.