Anatomical location of the abducens nerves (VI) in the ventral approach of clival tumors

The aim of this work was to determine reliable anatomical landmarks for locating and preserving the abducens nerves (6th cranial nerves) during trans-facial or trans-nasal endoscopic approaches of skull base tumors involving the clivus and the petrous apex. In order to describe this specific anatomy, we carefully dissected 10 cadaveric heads under optic magnification. Several measurements were taken between the two petro-sphénoidal foramina, from the bottom of the sella and the dorsum sellae. The close relationship between the nerves and the internal carotid artery were taken into account. We defined a trapezoid area that allowed drilling the clivus safely, preserving the 6th cranial nerve while being attentive to the internal carotid artery. The caudal part of this trapezium is, on average, 20 mm long at mi-distance between the two petro-sphenoidal foramina. The cranial part is at the sella level, a line between both paraclival internal carotid arteries. Oblique lateral edges between the cranial and caudal parts completed the trapezium.

Surgical anatomy for hemifacial spasm

Classically in the cerebello-pontine angle the facial (CN VII) and vestibular-cochlear (CN VIII) nerves should run parallel with the anterior inferior cerebellar artery, whereas the lower nerves (CN IX-XI) continue with the posterior-inferior-cerebellar artery (PICA). In fact, this is not always true, particularly when dealing with hemispasm surgery where the relationships between CN VII, CN VIII and PICA are often different and closer. Knowledge of anatomical bases in surgical situation will help neurosurgeons to appreciate anatomical nuances, that are important to increase effectiveness and safety of hemifacial spasm surgery.

Surgical anatomy of the petrous apex and petroclival region

Surgical exposure of the clivus, the ventral or lateral aspect of the brain stem, and all the intradural structures of the petroclival area remains difficult because of the presence of the petrous apex and peripetrous complex. However, a lateral skull base approach to the petroclival area is the most suitable approach if the lesion to be resected lies medial to the fifth nerve, in front of the acousticofacial bundles, extending towards the midline. The purpose of this study is to review the topographic anatomy of the petrous apex and peripetrous structures, with emphasis on the relationships important to the lateral approaches to the petroclival area. Such anatomical knowledge allows us to study the surgical technique, exposure, and pitfalls of the main lateral transpetrosal skull base approaches used to reach the petroclival area.