To describe a case of true fenestration of an extremely long anterior communicating artery (ACoA).

A 3-year-old boy with a history of a ventricular septal defect and aortic coarctation underwent magnetic resonance imaging (MRI) and angiography (MRA) of the head and neck regions using a 3-Tesla scanner, for follow-up of stenosis at the origin of the innominate artery, which was a complication of aortic arch coarctation surgery.

MRA of the head region showed an extremely long ACoA of approximately 20 mm in length, with a fenestration of approximately 5 mm in size. No aneurysms were observed.

According to a meta-analysis, the mean length of the ACoA was 2.84 mm (0.38–10.4 mm). The ACoA has been reported to be the most frequent site of fenestration of intracranial arteries. However, most reported ACoA fenestrations are not true fenestrations, but duplications or partial duplications. We herein report a case of true fenestration of an extremely long ACoA, which is an extremely rare variant. To our knowledge, this is the first report of such an association in the relevant English language literature.