Lateral posterior fossa venous sinus relationships to surface landmarks.

BACKGROUND: Knowing the location of the venous sinuses in the combined lateral posterior fossa and lateral cranial base approach is important to prevent their inadvertent injury. The identification of surface landmarks related to these structures is useful in planning such surgical approaches.
METHODS: Twelve injected adult cadaver specimens and 10 dried skulls were used to study the relationship of the venous sinuses to various surface anatomic structures.
RESULTS: The asterion was not clearly seen in 60% of the studied cadaver sides. The asterion was always clearly seen in the dry skull preparations. The upper margin of the superior nuchal line was found to range from 1.5 mm to 14 mm inferior to the lower margin of the lateral transverse sinus. In 85% of our specimens, the mastoid groove was found to completely overlie the sigmoid sinus.
CONCLUSIONS: The asterion was found to be variable in its anatomic relations to other identifiable structures. This variability in relation to other posterior fossa bony landmarks limits its overall usefulness as a consistently stable marker for intracranial structures. The first and most superolateral burr hole for lateral posterior fossa procedures can be safely placed 1 cm below the superior nuchal line and 1 cm medial to the top of the mastoid groove. A burr hole in this location will avoid the transverse and sigmoid sinuses, as well as the transverse-sigmoid junction, yet will be high enough and lateral enough to provide easy exposure of these venous sinuses for all lateral posterior fossa procedures.