Anterior and Middle Petrosectomy via an Extended Transorbital Neuroendoscopic Approach: Anatomic Study

Abstract

Background Transorbital neuroendoscopic (TONES) approaches have been described for resection of spheno-orbital, cavernous sinus, and Gasserian ganglion lesions. Lesions involving the petrous apex and cerebello-pontine angle (CPA) offer a formidable challenge via standard TONES approaches. This cadaveric study examined the surgical field-of-view and anatomic constraints provided by a novel extended transorbital neuroendoscopic (eTONES) approach and compared these to previously described TONES approaches and the traditional subtemporal anterior petrosectomy.Methods The eTONES approach includes single-piece removal of the superior and lateral orbital rims. This in turn offers expanded surgical trajectory to middle fossa skull base, anterior petrous ridge, and ventro-lateral posterior fossa, while reducing globe retraction. Four cadaveric heads underwent eTONES approach on one side and traditional subtemporal anterior petrosectomy on the contralateral side. Petrosectomy volume, location, and posterior fossa field-of-view were compared between the two approaches.Results Mean volume of petrous bone removed in the standard eTONES was 0.84 ± 0.38 ml. In comparison, the mean volume of petrous bone removed in the subtemporal approach was 0.72 ± 0.15 ml. On a single specimen, a superior eTONES variation was performed, tailored to provide access to the petrous apex and petroclival region, and 0.07ml of petrous bone was removed. Standard eTONES offered a straight on ventral-to-dorsal view of the internal acoustic canal and CPA contents. Conversely, traditional subtemporal approach, provided an unobstructed view of the medial CPA and petroclival region, with a lateral-to-medial viewing angle. Superior eTONES variation ‘bridges-the-gap’ between standard eTONES and subtemporal approaches in terms of petroclival and petrous apex exposure.Conclusion eTONES provides a straight on, minimally invasive endoscopic surgical approach that is comparable to the traditional subtemporal approach and may complement other surgical approaches for lesions involving the cavernous sinus, petroclival region, petrous ridge, and CPA. The describ¹ed approach has yet to be examined in a clinical setting.