Anatomical Step-by-step Dissection of Complex Skull Base Approaches For Trainees: Surgical Anatomy of the Anterior Petrosal Approach

Background: The anterior petrosal approach is a challenging approach that provides access to the posterior fossa through the middle fossa floor and petrous apex between the petrous portion of the internal carotid artery, the internal acoustic meatus and the lateral aspect of Meckel's cave. Although many descriptions of the anterior petrosal approach have been published, a practical step-by-step surgical guide that allows an easy understanding for skull base and neurosurgical trainees at different levels in their training is needed.

Methods: Three formalin-fixed, colored-injected specimens were utilized (six sides). The specimens were dissected under microscopic magnification. A middle fossa craniotomy and drilling of the petrous apex was performed and the anatomical dissection was documented in stepwise 3D photographic images. Following dissection, representative case applications were reviewed.

Results: The middle fossa exposure with anterior petrosectomy provides excellent access to lesions located in the trigeminal porus, Meckel's cave, superior petroclival area, superior cerebellopontine angle and ventrolateral midbrain and upper pons. The area to drill in the anterior petrosectomy approach forms a pentagon limited by the petrous internal carotid artery, cochlea, internal auditory canal, petrous ridge, and lateral border of V3. Key steps include: positioning and skin incision, scalp and muscle flap dissection, burr holes, craniotomy flap elevation, dura dissection along the petrous ridge, division of the meningeal artery, exposure of the greater superficial petrosal nerve, tegmen tympani, arcuate eminence and mandibular division of the trigeminal nerve. The anteromedial petrosectomy is performed, posterior fossa dura exposure and durotomy (in a T fashion: parallel to the superior petrosal sinus followed by dural division perpendicular and through the superior petrosal sinus) and final exposure.

Conclusions: The anterior petrosectomy is a complex approach that allows access to the posterior fossa through the middle fossa. Operatively oriented neuroanatomy dissections provide trainees with a critical foundation for learning this fundamental skull base technique. We describe a comprehensive step-by-step approach to learning this technique, intended to be easy to understand by an audience of all levels of knowledge and experience in a way that simultaneously assists with rapid learning in the operating room, and an understanding of its potential for wide clinical application to skull base diseases.