Ascending vermian artery, branch of the V4 segment of the vertebral artery.

A previously undescribed anatomical variant is reported here, that of vermian arteries (vAs) branched from the vertebral arteries (VAs) and replacing the medial branches of the posterior inferior cerebellar arteries (PICAs) that, in turn, were leaving the basilar artery. Both vAs left the VAs in the foramen magnum. The left vA initially looped in front of the spinal root of the accessory nerve (Sp11) and then looped inferiorly on the dorsal side of the spinal cord, in the vertebral canal and continued ascending on the dorsal surface of the medulla oblongata. The right vA looped dorsally to the Sp11 above the foramen magnum, and also ascended dorsally to the medulla. Both vAs were distributed to the vermis. On both sides, the PICAs looped above the glossopharyngeal nerves and the jugular foramina and continued as only lateral terminal branches of a normal PICA that descended in countercurrent on the outer side of the variant vAs. Such anatomical variation is relevant for surgery and microsurgery on both sides of the foramen magnum and in the posterior cerebral fossa.