Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Retrosigmoid Approach

Introduction: Neurosurgical anatomy is traditionally taught via anatomic and operative atlases; however, these resources present the skull base using views that emphasize 3D relationships rather than operative perspectives, and are frequently written above a typical resident's understanding. The goal of current study was to outline, step-by-step, a retrosigmoid dissection, presented from an operative perspective and described in accessible language, to aid junior level trainees with a valuable resource for laboratory and preoperative study alike.

Methods: Six sides of three formalin-fixed latex-injected specimens were dissected under microscopic magnification. A retrosigmoid craniotomy was performed by each of three neurosurgery residents, under supervision by the senior authors (C.L.D. and M.J.L.) and a graduated skull base fellow, neurosurgeon, and neuroanatomist (MPC). Dissections were supplemented with representative case applications ([Fig. 1)].

Results: The retrosigmoid craniotomy (aka, lateral suboccipital approach) affords excellent access to CN IV–XII, with corresponding applicability to numerous posterior fossa operations. Key steps include: positioning and skin incision, scalp and muscle flaps, burr hole and parasigmoid trough, craniotomy flap elevation, initial durotomy and deep cistern access, completion durotomy, and final exposure ([Fig. 2]).

Conclusion: The retrosigmoid craniotomy is a workhorse skull base exposure, particularly for lesions located predominantly in the cerebellopontine angle. Operatively oriented neuroanatomy dissections provide trainees with a critical foundation for learning this fundamental skull base technique. We outline a comprehensive approach for neurosurgery residents to develop their familiarity with the retrosigmoid craniotomy in the cadaver laboratory in a way that simultaneously informs rapid learning in the operating room, and an understanding of its potential for wide clinical application to skull base diseases ([Figs. 3] and [4]).

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