Foramen ovale morphology and relationship with the lateral pterygoid process plate: proposal for a new classification system

Surgeons frequently approach the foramen ovale (FO) via the infratemporal fossa (ITF) to treat trigeminal neuralgia. However, this percutaneous procedure could be unsuccessful due to anatomical factors. The present study aimed to assess the FO morphology and its relationship with the lateral pterygoid process plate (LPPP), emphasizing coexisting ITF variants. One-hundred-and-eight (216 sides) adult dried skulls were evaluated at the ITF (FO and LPPP). The FO maximum anteroposterior and lateromedial distances (APD and LMD) were calculated and correlated with the FO morphology. The FO-LPPP relationship was observed, and the presence of a sphenoidal emissary foramen (SEF) and possible ossified sphenoid bone's ligaments variants (pterygoalar and pterygospinous-PTA and PTS variable ossification) were recorded. Statistical analysis was performed using the SPSS statistical program. The FO morphology was classified into three types after taking into consideration the FO morphometry. Type 1 FO was considered when the APD was two times more than the LMD (45.83%), Type 2 FO was identified when the APD was more than the LMD but no more than two times (51.85%), and Type 3 FO was considered when the APD and LMD were equal (2.32%). The FO and LPPP relationships were classified into the following four types: the direct type when the LPPP base ended at the FO center (32.3%), the lateral type was observed when the LPPP base ended at the FO lateral margin (28.76%), the far type was considered when the LPPP base ended distally to the FO (22.57%), and the medial type was when the LPPP base ended at the FO medial margin (11.95% of cases). Concerning the impact of the sphenoid bone variants on the FO-LPPP, the SEF did not alter the FO-LPPP relationship, while the PTA or PTS bar presence significantly affected it (p < 0.001 and p = 0.007, respectively). When the sphenoid bone ossified bars were present, the most common type of FO was the medial one. A novel classification system was proposed for the FO morphology, assessing possible coexisting ITF variants that could alter the FO-LPPP relationship. Knowledge of these details would help clinicians perform percutaneous procedures to treat trigeminal neuralgia.