Double origin of the posterior inferior cerebellar artery with juxta-proximal fenestration of caudal component.

We demonstrate the first case of double origin of the posterior inferior cerebellar artery (PICA) with juxta-proximal fenestration of the caudal component, which was misunderstood as triple origin, combined with an unruptured middle cerebral artery aneurysm. The caudal component of the PICA originated from the atlanto-occipital portion and it was fenestrated shortly after origin. The cranial component originated from the intracranial vertebral artery and converged with the superior branch of the caudal component, and then met the inferior branch of the caudal component distally.