Typical and atypical neurovascular relations of the trigeminal nerve in the cerebellopontine angle: an anatomical study.

The aim of the present study was to anatomically evaluate in adults the neurovascular trigeminal relations in the cerebellopontine angle (CPA), from a morphological and topographical perspective and thus to improve, detail and debate the pre-existing information, with educational and surgical implications. For the present anatomical study we performed bilateral dissections on 20 human adult skull bases, in formalin-fixed cadavers, at the level of the cerebellopontine angle, using the anatomical superior approach; we also studied 20 additional drawn specimens-cerebellum and brainstems, from autopsied cadavers, in order to better document the vasculature at the trigeminal root entry zone (REZ). The most constant but not exclusive neurovascular relations of the trigeminal nerves were those with the superior cerebellar artery (SCA) and the superior petrosal vein (the petrosal vein of Dandy). The regular possibility for the SCA to appear divided into a medial and a lateral branch and these to represent individual trigeminal relations at the level of the pontine cistern or REZ must not be neglected. The petrosal vein tributaries can also represent superior, inferior, or interradicular trigeminal relations. Arterioles emerging from the SCA or the anterior inferior cerebellar artery (AICA) represented trigeminal relations either at the REZ or were coursing between the trigeminal roots. A dissected specimen presented a radicular trigeminal artery emerging from the basilar artery and entering the trigeminal cavum inferior to the nerve. Another specimen presented two bony lamellae superior to the trigeminal nerve at the entrance in the trigeminal cavum-these lamellae were embedded within the lateral border of tentorium cerebelli and the posterior petroclinoid ligament. So we bring here an evidence-based support extremely useful not only for specialists dealing with this area but also for educational purposes. It appears important not only to consider the typical anatomy at this level but also to take into account the atypical and hardly predictable morphologies that may alter the diagnoses and the specific surgical procedures.