Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Middle Fossa Approaches Including Internal Acoustic Canal Exposure and Anterior Petrosectomy

Background: The middle fossa approaches encompass a group of versatile and challenging surgical accesses to pathologies in the middle fossa, internal acoustic canal exposure, and superomedial aspect of the posterior fossa (anterior petrosectomy) or a combination. Although many descriptions of the middle fossa approaches have been published, a practical surgical guide that allows an easy understanding for skull base and neurosurgical trainees at different levels of training is needed.

Methods: Six sides of three formalin-fixed, colored-injected specimens were dissected under microscopic magnification. A middle fossa craniotomy followed by internal acoustic canal drilling was performed on three sides, and anterior petrosectomy was performed in the remaining three sides. The anatomical dissection was documented in stepwise 3D photographic images. Following dissection, representative case applications were reviewed.

Results: The middle fossa approach provides direct access to the middle fossa structures and internal acoustic canal. The 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. Key common steps include positioning and skin incision; scalp and muscle flaps; burr holes; craniotomy flap elevation ([Fig. 1]); dural dissection along the petrous ridge; and division of the middle meningeal artery and exposure of the greater superficial petrosal nerve, tegmen tympani, arcuate eminence, and mandibular division of the trigeminal nerve ([Fig. 2]). Then approach to the internal acoustic canal, superior internal acoustic canal drilling, and longitudinal dura opening ([Fig. 3]). The area drilled 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. After the anterior petrosectomy is performed, the dura is incised in four consecutive cuts with ligation of the superior petrosal sinus to expose the upper aspect of the posterior fossa ([Fig. 4]).

Conclusion: The middle fossa approaches are challenging. Operatively oriented neuroanatomy dissections provide trainees with a crucial foundation for learning these fundamental skull base techniques. In the current study, we described a comprehensive, step-by-step approach to mastering the middle fossa, internal acoustic canal exposure, and anterior petrosectomy, highlighted illustrative cases that emphasize their routine indications, and provided a detailed discussion of the various alternative approaches that may be considered by the contemporary skull base surgeon in attempting to individualize the operative strategies.

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Publication History

Article published online:
12 February 2021