Central myelin-peripheral myelin junction in trigeminal, facial, and vestibulocochlear nerve: A histo-morphometric study.

Background: The study aimed to locate the central myelin and peripheral myelin junction (CNS PNS Junction, CPJ) in trigeminal, facial and vestibulocochlear nerves.

Methods: The cisternal segments of the nerves were cut from the brainstem to the proximal margin of trigeminal ganglia (trigeminal nerve) and internal acoustic meatus (facial and vestibulocochlear nerve) from cadavers. Horizontal sections of H&E stained slides were analysed and histo morphometry was performed. The CPJ was confirmed by immunohistochemistry using monoclonal myelin basic protein antibody.

Results: The mean length of the trigeminal, facial and vestibulocochlear nerves were 13.6 ± 3.1 mm, 12.4 ± 1.9 mm and 11.5 ± 2.0 mm respectively; mean length of the centrally myelinated segment at the point of maximum convexity was 4.1 ± 1.5 mm, 3.7 ± 1.6 mm, 3.6 ± 1.4 mm respectively. Six different patterns were observed fortheCPJ.Utilizing the derived values, the CPJwas located at a distance of 18 - 48% and 17 - 61% of the total length of the nerve in all the cases in trigeminal and facial nerve respectively. In vestibulocochlear nerve, it was located at a distance of about 13 - 54% of the total length of the nerve.

Conclusions: The location of the CPJ in the vestibulocochlear nerve was midway between the brainstem and internal acoustic meatus which is a novel observation.For all the nerves, the CPJ was located either at or before the half way along the length of the nerve in huge majority (97%); never crossing the 60% of the nerve length.