Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Endoscopic Endonasal Approach to the Orbit

Background: The endoscopic endonasal approach to the orbit has been described in recent decades as an alternative route to the traditional external approaches to medial and inferior orbital lesions. Although several descriptions of endonasal approaches to the orbit have been published, the need remains for a practical, step-by-step surgical guide that allows neurosurgical trainees of different levels to understand this approach. Correspondingly, the main goal of the present project was to develop an educational resource to learn the endoscopic endonasal approach to the orbit via an operatively oriented easily understood dissection.

Methods: Three specimens were formalin fixed and injected with colored latex using a six-vessel technique. Six sides were dissected using 4-mm, 0- and 30-degree rigid endoscopic lenses (Karl Storz and Co.), standard endoscopic equipment, and a high-speed surgical drill (Medtronic Midas Rex electric systemÒ). The anatomical dissection was documented in stepwise 3D endoscopic images. Additional macroscopic 3D images were provided to further illustrate the neurovascular anatomical relationships from a medial ([Fig. 1]) and a lateral perspective ([Fig. 2]). Following dissection, representative case applications, as well as clinical pearls, for selection of this approach and tips for prevention and treatment of complications were thoughtfully reviewed.

Results: The endoscopic endonasal route provided an excellent access to the medial and inferior orbital regions and to the medial aspect of the orbital apex and optic canal. The precise anatomical relation of the orbital lesion to the optic nerve and conal structures must be assessed, as appropriate case selection and understanding the limitations of this endoscopic endonasal corridor are the key factors for its optimal use. Key surgical steps included: positioning and preoperative considerations, middle turbinate medial dislocation, uncinate process and ethmoid bulla removal, complete ethmoidectomy, transethmoidal sphenoidotomy, maxillary antrostomy, medial maxillectomy, lamina papyracea removal, orbital apex and optic canal decompression, orbital floor removal, periorbita opening, dissection of the extraconal fat, and final exposure of the orbit contents between the medial and inferior rectus muscles ([Fig. 3]). Reconstruction techniques, although not routinely required, and the nasal packing procedure were also described.

Conclusion: The endoscopic endonasal approach to the orbit is challenging. Operatively oriented neuroanatomy dissections are crucial for learning the anatomy and fundamental skills of this practical minimally invasive endonasal corridor. We describe a comprehensive step-by-step curriculum directed to residents, fellows, and any audience willing to master this endoscopic skull base approach.

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Publication History

Article published online:
12 February 2021