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 extradural origin of the PICA is infrequent. Its preoperatory identification is important in surgical strategy during the exposure of the VA.

METHODS

During an anatomic prosection, the VA was exposed at the craniocervical junction in cadaveric adult specimens. The extradural origin of the PICA was encountered bilaterally in one specimen and on one side in a second specimen. An anatomic study with histological and radiographic 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 infarction of these neural structures that can be asymptomatic or cause major neurological deficits. Radiographic results obtained using a lateral projection provided the most reliable delineation of the extradural origin of the PICA. When this artery originates at, or posterior to, the posterior aspect of the occipital condyle, an extradural origin is likely.

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 without question. A thorough understanding of the relative dominance of the VAs and PICAs, the location of the PICA origin, and the collateral circulation of the posterior fossa are prerequisites to surgery in this region. The preoperative identification of an extradural PICA is important in planning surgical strategy and in avoiding complications during operations near the foramen magnum.