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

Abstract

Introduction Neurosurgical anatomy is traditionally taught via anatomic and operative atlases; however, these resources present the skull base using views that emphasize three-dimensional (3D) relationships rather than operative perspectives, and are frequently written above a typical resident's understanding. Our objective is to describe, step-by-step, a retrosigmoid approach dissection, in a way that is educationally valuable for trainees at numerous levels. Methods Six sides of three formalin-fixed latex-injected specimens were dissected under microscopic magnification. A retrosigmoid was performed by each of three neurosurgery residents, under supervision by the senior authors (C.L.W.D. and M.J.L.) and a graduated skull base fellow, neurosurgeon, and neuroanatomist (M.P.C.). Dissections were supplemented with representative case applications. Results The retrosigmoid craniotomy (aka lateral suboccipital approach) affords excellent access to cranial nerve (CN) IV to 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. 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.

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

“…Taken together, these considerations render the retrosigmoid our preferred approach for most CPA surgeries, with the far lateral reserved for low, ventral lesions, and the presigmoid exposures selected when a more anterolateral trajectory is needed for central or upper CPA lesions, as we have previously described ( Table 1 ). 2 4 Of note, due to the low and ventral exposure, the far lateral also incurs an increased risk of extracranial facial nerve injury during dissection; although rare, this injury is potentially devastating, and deliberate care is required to avoid heat, stretch, or other injury, particularly while exposing the mastoid tip.…”

“…With the scalp flap elevated and the C1-2 region fully exposed, attention is turned to the craniotomy which begins with a standard retrosigmoid bone flap, as we have previously described. 2 A large burr hole is placed at the inferomedial angle of the transverse-sigmoid junction, with the borders of both sinuses visualized unambiguously (►Fig. 1E).…”

“…1 The far lateral is perhaps best understood as an expanded version of its more commonplace counterpart, the standard retrosigmoid craniotomy. 2 Both approaches access the posterior fossa via a trajectory centered posterior to the sigmoid sinus, minimizing the need for temporal bone drilling and reducing the risk of hearing loss directly attributable to the exposure.…”

3D Printing for Complex Cranial Surgery Education: Technical Overview and Preliminary Validation Study

“…17 18 19 Although this need is addressed in part by our previously described step-by-step anatomic dissection guides, absent the resources of a cadaver laboratory, the added value of a physical model that can be manipulated, examined, positioned, and so on in 3D space is considerable, when compared to 2D images alone. 1 2 3D printed models provide not only visual information but haptic tactile perception that has been shown to aid in greater understanding than visualization of data on 2D screens. 20 21 22…”

Application of Subperineural Resection Technique in Vestibular Schwannomas: Surgical Efficacy and Outcomes in 124 patients

“…Lumbar cistern drainage was performed routinely before surgery. A craniotomy was conducted with a suboccipital retrosigmoid approach in the lateral prone position intraoperatively ( 16 ). The transverse sinuses and the intersection of transverse and sigmoid were located on the basis of MRI.…”