Endoscopic endonasal approach to the ventral-medial portion of posterior paramedian skull base: a morphometric perspective of surgical and radiological anatomy

Objective: This study aims to provide morphometric analysis of endoscopic endonasal approach (EEA) to ventral-medial portion of posterior paramedian skull base (VMPPSB). 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 pre-dissection and a post-dissection CT study was performed. A surgically oriented classification into 4 regions was used: 1) tubercular region; 2) occipital condyle region; 3) parapharyngeal space (PPhS) region; 4) jugular foramen (JF) region. Student's 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 VMPPSB encompasses two medial trajectories (transtubercular and transcondylar) and two lateral pathways to PPhS and JF. The CN access, without removal of ET, allows a complete exposure of petrous and intrajugular portion of JF and superior PPhS without exposition of parapharyngeal segment of internal carotid artery. The ipsilateral nostril approach with ET removal allows to obtain a wider exposure, reaching medial sigmoid part of JF. No significant differences exist in regards to transtubercular and transcondylar approaches. Conclusions: This study suggests that EEA to PPSB allow the realization of a corridor directed to jugular tubercle, occipital condyle, medial parapharyngeal space and ventral-medial JF. The CN approach with ET preservation can expose petrous and intrajugular parts of JF and PPhS. Case series are needed to demonstrate benefits and drawbacks of these approaches