The basilar venous plexus.

The basilar venous plexus is the anteromedian venous channel of the posterior cranial fossa that has many conflicting and brief descriptions in the extant literature. To our knowledge, no single study has been performed that analyzed this venous structure in detail. The aim of the current study was to elucidate further the anatomy of this structure of the posterior cranial fossa. The authors examined twenty adult cadaveric specimens following injection of the internal jugular veins or cavernous sinus to observe the morphology of the basilar plexus. All specimens were found to have a basilar plexus which was always plexiform and very variable in nature. This structure was dorsal to the clivus superiorly and dorsal clivus and overlying tectorial membrane inferiorly. The mean diameter of the channels making up this plexus was 1.1 mm. Communication was always found between the basilar plexus and the inferior petrosal sinuses and this was the primary route used to drain the basilar sinus out of the cranium. In fact, these two venous structures were more or less contiguous across the midline at multiple levels. In seven specimens (35%), the basilar plexus communicated with veins draining into the hypoglossal canal. The basilar plexus communicated with the marginal sinus in 12 specimens (60%). This plexus became much less concentrated as it descended inferior to a plane between the jugular tubercles. No specimen was found to have connections with veins of the anterior brain stem or ventral surface of the clivus. The basilar plexus is a highly variable posterior fossa venous structure. Clinicians and radiologists should take into account this variability when managing cerebral venous disorders or interpreting imaging studies of the skull base.