Surgical Anatomy of the Retrosigmoid Approach with Endoscopic-Assisted Reverse Anterior Petrosectomy (RAP): Optimizing Meckel's Cave Access from the Posterior Fossa

Purpose: The Retrosigmoid Approach with Endoscopic-Assisted Reverse Anterior Petrosectomy (RAP) is an approach used to treat lesions extending from the cerebellopontine angle to the middle cranial fossa (MCF). This study aims to investigate the extent of access to Meckel’s cave (MC) and the MCF while providing guidance for intraoperative protection of the internal carotid artery (ICA).

Methods: Ten sides of five formalin-fixed, latex-injected anatomical specimens were dissected. Two different variations of the RAP were performed according to the inferior and lateral extensions of the petrous bone removed: the limited RAP, in which the internal acoustic meatus (IAM), inferiorly, and the base of the suprameatal tubercle (SMT) and subarcuate fossa (SF), laterally, were preserved; the extended RAP, in which the same aforementioned limits were removed, thereby exposing the CN VII/VIII complex and the semicircular canals, respectively. Retrosigmoid craniotomies with limited and extended RAP were performed to measure various distances to the MC and ICA and compared. Temporal craniotomies with an extradural subtemporal approach were subsequently performed to provide visualization of access from the MCF to this region for further analysis. Digital measurements were obtained and analyzed using ImageJ.

Results: In the limited RAP, defined by SMT and SF preservation, the superoanterior zone of MC was accessed with a mean distance to the superior orbital fissure and foramen rotundum of 2.5 cm and 2.0 cm, respectively. Meanwhile, preserving the IAM inferiorly allowed access to the inferolateral zone of MC with a mean distance to the foramen ovale of 0.8cm. In the extended RAP, after the removal of the IAM and SF, the corridor between CN V and CN VII/VIII complex allowed access to the inferolateral zone of MC with a mean distance to the foramen ovale of 1.2 cm. The maximal length of the lacerum and petrous ICA exposed in the extended RISA were 0.3 cm and 0.9 cm, respectively. In both RAP variations, drilling between the SMT and the petrous ridge accessed the superomedial zone of MC, with a mean distance of 0.7 cm to the posterior bend of the cavernous ICA.

Conclusion: Our results suggest that extended inferolateral drilling of the petrous apex provides greater access to V3 in MC, yet with increased risk for iatrogenic injury to the ICA. Following the removal of the base of the SMT, the point at which MC contacts the lacerum ICA is found inferomedially. Instead of proceeding in this inferolateral trajectory, drilling in an anterior and superior direction to achieve greater MCF access is recommended to avoid petrous ICA injury.

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No conflict of interest has been declared by the author(s).

Publication History

Article published online:
05 February 2024