Endoscopic Endonasal Approach to the Ventral-Medial Portion of Posterior Paramedian Skull Base: A Morphometric Perspective of Surgical and Radiologic Anatomy

Objective: This study aims to provide morphometric analysis of endoscopic endonasal approach (EEA) to the ventral-medial portion of posterior paramedian skull base. Furthermore, it aims to investigate the surgical exposure obtained through EEA with and without eustachian tube (ET) removal, emphasizing the role of contralateral nostril (CN) access. Methods: Five fresh adult head specimens were prepared for dissection. A predissection and a postdissection computed tomography study was performed. A surgically oriented classification into 4 regions was used: 1) tubercular region; 2) occipital condyle region; 3) parapharyngeal space (PPhS) region; and 4) jugular foramen (JF) region. The Student t-test was used to compare angulations and measures of EEA with access from the ipsilateral and CN, respectively, with and without ET removal. Results: EEA to the ventral-medial portion of posterior paramedian skull base encompasses 2 medial trajectories (transtubercular and transcondylar) and 2 lateral pathways to the PPhS and JF. The CN access, without removal of the ET, allows a complete exposure of the petrous and intrajugular portion of the JF and superior PPhS without exposition of the parapharyngeal segment of internal carotid artery. The ipsilateral nostril approach with ET removal allows to obtain a wider exposure, reaching the medial sigmoid part of the JF. No significant differences exist in regard to transtubercular and transcondylar approaches. Conclusions: This study suggests that EEA to posterior paramedian skull base allows the realization of a corridor directed to the jugular tubercle, occipital condyle, medial PPhS, and ventral-medial JF. The CN approach with ET preservation can expose the petrous and intrajugular parts of the JF and PPhS. Case series are needed to demonstrate benefits and drawbacks of these approaches. Keywords: Anatomy; Endoscopic endonasal approach; Eustachian tube; Internal carotid artery; Posterior paramedian skull base.