A standalone minimally invasive presigmoid retrolabyrinthine suprameatal approach: A cadaveric morphometric study.

Background: Presigmoid approaches provide access to several structures anterior to the sigmoid sinus (SS) and may be intended for the treatment of lesions located in the middle and posterior fossa. We conducted a morphometric cadaveric study investigating the infratentorial presigmoid retrolabyrinthine suprameatal approach (PRSA) as a unique operative corridor. The typical anatomic-radiological characteristics and variations were evaluated and analyzed to predict surgical accessibility.

Methods: A total of 10 surgical dissections were performed on both sides of five adults, injected, and cadaveric heads. Fifteen morphometric parameters were measured, analyzed, and categorized into pre-procedural, intra-procedural, and additional parameters.

Results: Preoperative anatomic-radiological parameters provide valuable information to select patients with favorable anatomy that may offer appropriate surgical accessibility to the medial part of cerebellopontine angle cistern, lateral pons, and prepontine cistern through a PRSA corridor. An obtuse petroclival angle of ≥144° with a more horizontally oriented petrous bone, a posterior SS position, and a large mastoid cavity provided the greatest surgical accessibility through the PRSA corridor. The superior petrosal sinus drainage and the degree of petrous apex pneumatization were important factors affecting surgical fluency and speed. However, they were not determinant factors for selecting the most appropriate patients eligible for the PRSA.

Conclusion: The PRSA represents a minimally invasive modification of the trans-labyrinthine approach that may be offered in patients with lesions medial to the internal auditory canal or anterior/lateral to the brainstem, with the goal of preserving vestibulocochlear functions. Preoperative anatomic-radiological parameters are mandatory for a patient-tailored selection of the most effective surgical approach.