Background: Dural venous sinuses around the torcular herophili area must be preserved during routine craniotomy such as suboccipital approach, supracerebellar approach. Localization of these venous sinuses is usually guided by surgical landmarks such as inion, superior nuchal line and asterion.

Objective: The present study aimed to demonstrate the accuracy of routine surface landmarks in estimating the exact location of these dural venous structures in the Thai population.

Materials and Methods: Fifty-one formalin-fixed skulls were studied in their bony landmarks around the torcular area. Surgical landmarks included lambdoid sutures, inion, and superior nuchal lines within 3.5 cm lateral from the inion bilaterally. The transverse sinuses were measured in relation to the surface landmarks by using vernier calipers.

Results: Inion is located at the torcular herophili area 68.6%, inferior to the torcular herophili 19.6% and superior to the torcular herophili 11.8%. The right superior nuchal line located at the transverse sinus 68.6%, inferior to the sinus 13.7%, and superior to the sinus 17.7%. The left superior nuchal line located at the transverse sinus 66.7%, inferior to the sinus 9.8%, and superior to the sinus 23.5%. Lambdoid sutures located superior to the sinuses 3.5 cm on the right and 3.8 cm on the left. The width of the right transverse sinus was greater than the left transverse sinus significantly. (p<0.05).

Conclusion: Inion and superior nuchal lines were roughly useful landmarks for torcular herophili and transverse sinuses. Right transverse sinus is larger than the left transverse sinus. Lambdoid suture is not a good landmark for these venous sinuses. Without availability of the neuro-navigator, burr holes of adult craniotomy should be placed inferior to the superior nuchal line at least 15 mm to avoid transverse sinuses and cut the bone at least 8 mm below inion to avoid torcular herophili for routine midline posterior fossa surgery.

Keywords: Torcular herophili; Transverse sinus; Inion; Superior nuchal line