Anterior petrosal approach: The safety of Kawase triangle as an anatomical landmark for anterior petrosectomy in petroclival meningiomas.

Object: Anterior petrosectomy through the middle fossa is a well-described option for addressing cranial base lesions of the petroclival region. To access posterior fossa through middle fossa, we quantitatively evaluate the safety of Kawase triangle as an anatomical landmark.

Method: We reviewed pre- and postoperative Multi-Slice CT scan (1mm thickness) of patients with petroclival meningioma between Jan 2009 and Sep 2013 in which anterior petrosectomy was performed to access the posterior fossa part of the tumor. The distances between drilling start and finish edge to the vital anatomical skull base structures such as internal auditory canal (IAC) and superior semicircular canal and petrous apex (petrous part of the carotid artery) were measured and analyzed.

Results: Drilling entrance length is directly related with tumor size. The distances between anatomical structures and drilling points decrease with increasing tumor size, but it always remains a safe margin between drilling points and IAC, internal carotid artery (ICA), and semicircular canals in axial and coronal views.

Conclusion: The Kawase triangle is shown to be a safe anatomical landmark for anterior petrosectomy. The described landmarks avoid damage to the vital anatomical structures during access to the posterior fossa through middle fossa, despite temporal bone anatomical variations and different tumor sizes.