Background: Anatomical localization of the venous sinuses in the posterior cranial fossa is important to preventing inadvertent
venous sinus injury during surgical approaches to the area. Identification of surface landmarks related to these structures is
useful in planning such approaches.
Objective: To identify the positions of the asterion and the superior nuchal line for localization of the venous sinus in the
posterior fossa.
Material and Method: Twenty fresh cadaveric heads, yielding 40 sides, were used. The vessels were injected with colored
silicone. The soft tissues were removed to expose the posterior cranium, from inion to the foramen magnum and laterally to
the mastoid process. Using digital calipers, the relationship of asterion to the transverse-sigmoid sinus junction was determined and the distance from the highest superior nuchal line to the nearest transverse sinus was measured.
Results: Asterion was located in 82.5% of the cadavers on the right side and 85.0% on the left side. The most common asterion position was at the junction of the transverse and sigmoid sinuses (67.5%), of which 5.0% were superior to the
transverse-sigmoid junction, 2.5% inferior to the transverse-sigmoid junction and 7.5% medial to the transverse-sigmoid
junction, at the transverse sinus. The superior nuchal line was identified in all cadavers. The most common position was inferior to the transverse sinus (60.0%) at an average distance of 8.55 mm 35.0% were at the same level as the transverse sinus and 5.0% were superior to the transverse sinus at an average distance of 2.14 mm.
Conclusion: A burr hole inferior-medial to asterion can expose the posterior fossa dura with the least risk. The superior nuchal line is always identifiable and relatively close to the transverse sinus. A burr hole more than 3 mm inferior to the superior nuchal line can expose the posterior fossa dura with the least risk.

Keywords: Posterior cranial fossa, Retrosigmoid approach, Venous injury, Surgical safety