[Unruptured aneurysm arising from fenestration of the horizontal (A1) segment in the anterior cerebral artery: a case report and review of the literature].

Cerebral aneurysms arising from fenestration of the horizontal (A(1)) segment in the anterior cerebral artery (ACA) are very rare. In this paper, we report our case, discuss radiological features, and review previous cases. A 70-year-old male was referred to our hospital presenting with memory disturbance. His unruptured cerebral aneurysm in the A(1) segment was incidentally found by magnetic resonance angiography (MRA). Three dimensional computed tomographic angiography (3D-CTA) demonstrated this aneurysm arising from fenestration of the A(1) segment. Surgical neck clipping was performed via the pterional approach, while sacrificing one pair of the A(1) segment. The patient's post operative course was uneventful. Only 14 cases with an aneurysm arising from fenestration of the A(1) segment have been reported previously. In the present case, 3D-CTA was very useful for finding out where the aneurysm arose from, and we also had to be careful about perforating arteries from the A(1) segment during the surgery.