Microsurgical anatomy of the extracranial-extradural origin of the posterior inferior cerebellar artery.

OBJECT: The authors describe the microsurgical anatomy of the posterior inferior cerebellar artery (PICA) with an extradural origin and discuss its importance as a common variation.

METHODS: The microsurgical anatomy of paired PICAs with an extradural origin were examined.

CONCLUSIONS: Five to 20% of PICAs have an extradural origin. In the case described, both PICAs arose extradurally from the third segment of the vertebral artery (VA). Both origins were less than 1 cm proximal to the site at which the VA penetrated the dura, and neither PICA gave rise to extradural branches. Extradurally, the PICAs coursed parallel to the VA and the C-1 nerve and the three structures penetrated the dura together. Intradurally, the PICAs remained lateral and posterior to the brainstem, whereas, in the common PICA configuration, the first segment of the PICA courses anterior to the medulla. Neither PICA sent branches to the anterior brainstem, which is commonly found in PICAs with an intradural origin. There were no soft-tissue or bone anomalies.