Original landmarks for intraoperative localization of the foramen ovale: a radio-anatomical study.

PURPOSE: Radiofrequency lesioning is one of the frequently used modalities for the treatment of trigeminal neuralgia. Easily identifiable radiological landmarks are necessary for correct intra-operative localization of foramen ovale.

METHODS: One hundred and seventy sides of dry skulls were studied for the following measurements. D-1: the transverse distance between the apex of the petrous temporal and the centre of the foramen ovale. D-2: the transverse distance from the midline to the centre of the foramen ovale. The distances between the centre of the foramen ovale and, D-3: the anterior margin of mandibular fossa, D-4: centre of the mandibular fossa and D-5: point at the junction of posterior margin and floor of the sella. D-6: the vertical distance between the centre of the foramen ovale and point at the junction of posterior margin and floor of the sella.

RESULTS: The mean values measured were D-1: 13.9 mm, D-2: 24.5 mm, D-3: 3.1 mm, D-4: 11.4 mm, D-5: 0.75 and D-6: 12.42 mm. In majority of cases the centre of foramen was around 25 mm from midline. Additionally the centre of the foramen was at the level of the junction of the posterior wall and floor of the sella or within 2 mm of this point in the antero-posterior direction. In most (81%) cases the vertical displacement of the foramen was 1-1.5 cm inferior to this point.

CONCLUSION: During intra-operative imaging, the midline of the skull and the junction of the posterior wall and floor of the sella can be used as reliable landmarks for the identification of foramen ovale.