Surgical Implications of Anatomic Relationships Among Foramen Ovale, Foramen Spinosum, and VI Cranial Nerve in the Anterior Transpetrosal Approach

BACKGROUND AND OBJECTIVE: The anterior transpetrosal approach (ATA) is a valuable option for accessing the petroclival region, although it can be associated with considerable morbidity. The objective of the study was to provide a detailed description of the anatomic relationship between key neurovascular structures encountered in the ATA, to facilitate crucial steps of the approach. METHODS: ATA has been performed on 34 sides in cadaveric heads. The extent of drilling was divided into standard ATA and extended ATA with removal of the petrous apex below the mandibular nerve (V3) and Gasserian ganglion. The relationship between middle meningeal artery and foramen spinosum (FS), greater superficial petrosal nerve (GSPN), foramen ovale, and arcuate eminence was evaluated. Finally, the abducens nerve (CN VI) was analyzed in its cisternal and interdural segment (CN VI-IS). RESULTS: The FS was located posterolateral to the foramen ovale at a mean distance of 3.5 mm. The mean FS distances from the craniotomy edge and the arcuate eminence measured 24 and 29 mm, respectively. The mean distance between the FS and the GSPN-V3 intersection was 6.2 mm. At the root exit zone of CN VI, the mean distance from the inferior petrosal sinus was 7.8 mm. At the petrous apex, CN VI lay 9.7 mm deep to the Gasserian ganglion before passing beneath Gruber's ligament. The mean length of the CN VI-IS was 6.6 mm, and according to its exposure obtained with standard or extended ATA, it was divided into 3 patterns. CONCLUSION: An understanding of the relationship among the middle meningeal artery, V3, GSPN and CN VI is essential to reduce operative time and neurological morbidity. The CN VI with a longer CN VI-IS could represent a potential risk factor for indirect injury during aggressive bone removal in the ATA.