EXTRADURAL ORIGIN OF THE POSTEROINFERIOR CEREBELLAR ARTERY - AN ANATOMIC STUDY WITH HISTOLOGICAL AND RADIOGRAPHIC CORRELATION

OBJECTIVE: The posteroinferior cerebellar artery (PICA) usually arises from the intradural segment of the vertebral artery (VA), The extradu ral origin of the PICA is infrequent. Its preoperatory identification is important in surgical strategy during the exposure of the VA. METHO DS: During an anatomic prosection, the VA was exposed at the craniocer vical junction in cadaveric adult specimens. The extradural origin of the PICA was encountered bilaterally in one specimen and on one side i n a second specimen. An anatomic study with histological and radiograp hic correlation was performed. RESULTS: Perforating branches originate from the PICA. They supply the middle and inferior third of the olive and the lateral aspect of the medulla. The PICA has cortical branches that lead to the cerebellum. Injury to the PICA can produce an infarc tion of these neural structures that can be asymptomatic or cause majo r neurological deficits. Radiographic results obtained using a lateral projection provided the most reliable delineation of the extradural o rigin of the PICA. When this artery originates at, or posterior to, th e posterior aspect of the occipital condyle, an extradural origin is l ikely. CONCLUSION: Bilateral selective vertebral angiography should be performed with special attention to the relationships of PICA origins before any surgical exposure of the VA at the craniocervical junction , unless magnetic resonance angiography provides this information with out question. A thorough understanding of the relative dominance of th e VAs and PICAs, the location of the PICA origin, and the collateral c irculation of the posterior fossa are prerequisites to surgery in this region. The preoperative identification of an extradural PICA is impo rtant in planning surgical strategy and in avoiding complications duri ng operations near the foramen magnum.