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Anatomical study of the central myelin portion and transitional zone of the vestibulocochlear nerve

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Abstract

Background

The aim of this study was to evaluate gross and microscopic anatomical features of the vestibulocochlear nerve or eighth cranial nerve (CNVIII) from fresh cadavers, especially the nerve’s central myelin portion (CMP) and transitional zone (TZ), and to consider any pathological implications.

Methods

Six fresh cadavers were used to examine the CNVIII. Its cisternal length from brainstem to internal auditory meatus was measured. Longitudinal sections were stained to make following measurements: the diameter where the nerve enters the brainstem, the diameter where the TZ begins, the distance to the most distal part of TZ from the brainstem, and the depth of the TZ. The volume of the CMP was calculated as well.

Results

The cisternal length of ten CNVIIIs measured between 14.2 and 19.2 mm (16.48 ±1.78 mm). The thickness where the CNVIII enters the brainstem was between 1.21 and 3.16 mm (2.31 ± 0.68 mm); the thickness where the TZ begins was between 1.07 and 2.21 mm (1.44 ± 0.38 mm); the distance of the most distal part of the TZ from the brainstem was between 9.28 and 13.84 mm (11.50 ± 1.56 mm); the depth of the TZ was between 0.56 and 1.28 mm (0.81 ± 0.27 mm). The volume of the CMP was between 17.34 and 53.87 mm3 (33.98 ± 13.74 mm3). The measurements were compared to trigeminal, facial, glossopharyngeal and vagus nerves. CNVIII was the nerve with the longest CMP.

Conclusions

The measurements showed that the CMP of CNVIII was very long. The implication of this length in the dysfunctional syndromes of this nerve, its propensity to harbor schwannomas, which most frequently arise at the porus of the auditory meatus, and the vulnerability to damages are discussed.

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Authors and Affiliations

  1. Department of Neurosurgery, Hopital Neurologique Pierre Wertheimer, University of Lyon 1, Lyon, France

    Bulent Guclu, Marc Sindou, Emile Simon & Patrick Mertens

  2. Hospices Civils de Lyon, Centre de Pathologie et de Neuropathologie Est, Lyon, 69003, France

    David Meyronet & Nathalie Streichenberger

  3. Inserm U1028; CNRS UMR 5292, Neuroscience Center, University Lyon 1, Lyon, 6900, France

    David Meyronet & Nathalie Streichenberger

  4. Department of Anatomy, University of Lyon 1, Lyon, France

    Emile Simon & Patrick Mertens

  5. Neurosurgery Clinic, Ministry of Health, Sevket Yilmaz Research and Training Hospital, Yildirim, Bursa, 16310, Turkey

    Bulent Guclu

Authors
  1. Bulent Guclu
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  2. Marc Sindou
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  3. David Meyronet
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  4. Nathalie Streichenberger
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  5. Emile Simon
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  6. Patrick Mertens
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Corresponding author

Correspondence to Bulent Guclu.

Additional information

Comment

Guclu and colleagues from the University of Lyon report the results of a microscopic anatomy study on the length of central myelin of the VIIIth cranial nerve. This study completes a series of volumetric analyses of the central myelin of the cranial nerves and confirms that the central myelin portion of the vestibulocochlear nerve is the longest.

The authors suggest that this feature may predispose the VIIIth cranial nerve to dysfunctional syndromes, such as positional vertigo and tinnitus, and its peculiar vulnerability to mechanical injuries. Also, the authors suggest its role in the susceptibility of the vestibulocochlear nerve to the development of schwannomas. The hypothesis is attractive, but it needs to be verified by more comprehensive studies.

One point, however, deserves attention: the embryologic origin of the nerve and its possible influence on the development of vestibular schwannomas. This and other well-known studies showed that schwannomas develop at the glio-schwannian junction. Here, in particular circumstances, Schwann cells develop some potential to generate proliferative tumor cells. Therefore, we can infer that in this small area, there are environmental factors, including an irregular glio-schwannian interaction, contributing to the development of tumors.

Alfredo Conti Messina, Italy

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Guclu, B., Sindou, M., Meyronet, D. et al. Anatomical study of the central myelin portion and transitional zone of the vestibulocochlear nerve. Acta Neurochir 154, 2277–2283 (2012). https://doi.org/10.1007/s00701-012-1479-x

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  • DOI: https://doi.org/10.1007/s00701-012-1479-x

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