Objectives: The Petroclival lesions are difficult to excise surgically because of their location. Anterior petrosectomy by an extradural subtemporal route is the standard procedure for removal of Petroclival meningiomas but has many complications. This cadaveric study was done to identify landmarks for safe surgeries using intradural approach via the transylvian-transtentorial route for petroclival lesions. As neurosurgeons are more comfortable with transsylvian approaches and the corridor is definitely wider through this approach. Patients and Methods: This study was conducted in the department of anatomy over a period of two years. Cadaveric anterior intradural petrosectomy was conducted in 13 complete unfixed heads (26 sides), important anatomical landmarks for anterior intradural petrosectomy were identified and distance between these landmarks were measured and recorded as D1 to D7. Results: Cadaveric dissection of skull was performed on 13 cadavers (26 sides). Eight males (16 sides) and five females (10 sides). No significant difference was found in measurements between males and females. In most specimens the distance was between 10-13 mm from the entry of the third nerve to the fourth nerve. In practice a cut on the tentorial edge > 1.7 cm will not injure the fourth nerve. The distance of dura cut from tentorial edge to superior petrosal sinus was 09 to 22 mm (mean 13.96 mm). Total dura to be cut from tentorial edge was 21 to 40 mm (mean 27.57 mm). Distance from petrous ridge to superior medial edge of internal auditory meatus (IAM) was found to range from 05 to 15 mm (mean 09.03mm). Internal carotid artery (ICA) was found at a minimum distance of 04 mm with a mean of 08.88mm from the point of drilling on petrous ridge. The distance from lateral edge of gassarian ganglion (GG) to the arcuate eminence was between 16 to 28 mm (mean 21.5 mm) Conclusions: In order to avoid injury to nerves, ICA and brainstem, dura should be cut at right angles just proximal to fourth nerve, arcuate eminance (AE) identified and dura stripped. Drilling should be done from petrous ridge, not more than 05mm deep, not more than 04 mm laterally, should not exceed 07 mm towards GG and should lie inside the line joining arcuate eminence (AE) to petrous ridge.

Keywords: Petroclival Region; Gassarian Ganglion (GG); Internal Carotid Artery (ICA), Arcuate Eminence (AE); Intradural Anterior Petrosectomy; Internal Auditory Meatus (IAM).