J Korean Neurosurg Soc.  2014 May;55(5):244-247. 10.3340/jkns.2014.55.5.244.

Microanatomy and Histological Features of Central Myelin in the Root Exit Zone of Facial Nerve

• Yee GT
• Yoo CJ
• Han SR
• Choi CY

• KMID: 2018028
• DOI: http://doi.org/10.3340/jkns.2014.55.5.244

Abstract

OBJECTIVE
The aim of this study was to evaluate the microanatomy and histological features of the central myelin in the root exit zone of facial nerve.
METHODS
Forty facial nerves with brain stem were obtained from 20 formalin fixed cadavers. Among them 17 facial nerves were ruined during preparation and 23 root entry zone (REZ) of facial nerves could be examined. The length of medial REZ, from detach point of facial nerve at the brain stem to transitional area, and the thickness of glial membrane of central myelin was measured. We cut brain stem along the facial nerve and made a tissue block of facial nerve REZ. Each tissue block was embedded with paraffin and serially sectioned. Slices were stained with hematoxylin and eosin (H&E), periodic acid-Schiff, and glial fibrillary acid protein. Microscopy was used to measure the extent of central myelin and thickness of outer glial membrane of central myelin. Thickness of glial membrane was examined at two different points, the thickest area of proximal and distal REZ.
RESULTS
Special stain with PAS and GFAP could be differentiated the central and peripheral myelin of facial nerve. The length of medial REZ was mean 2.6 mm (1.6-3.5 mm). The glial limiting membrane of brain stem is continued to the end of central myelin. We called it glial sheath of REZ. The thickness of glial sheath was mean 66.5 microm (40-110 microm) at proximal REZ and 7.4 microm (5-10 microm) at distal REZ.
CONCLUSION
Medial REZ of facial nerve is mean 2.6 mm in length and covered by glial sheath continued from glial limiting membrane of brain stem. Glial sheath of central myelin tends to become thin toward transitional zone.

Keyword

Central myelin; REZ; Facial nerve; Glial sheath

MeSH Terms

Brain Stem
Cadaver
Eosine Yellowish-(YS)
Facial Nerve*
Formaldehyde
Glial Fibrillary Acidic Protein
Hematoxylin
Membranes
Microscopy
Myelin Sheath*
Paraffin
Eosine Yellowish-(YS)
Formaldehyde
Glial Fibrillary Acidic Protein
Hematoxylin
Paraffin

Figure

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  Fig. 1 Photograph showing an exiting facial nerve (CN VII) from pontomedullary junction.

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  Fig. 2 Photomicrograph showing an exiting facial nerve from brain stem. A : Central segment of facial nerve positive to glial fibrillary acid protein (arrow) turned out to be a brown color and peripheral segment is not stained (arrowhead). B : Peripheral segment of facial nerve positive to periodic acid-Schiff (arrow) turned out to be a deep purple color (original magnification, ×10).

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  Fig. 3 The length of medial root exit zone, from detach point of facial nerve at the brain stem to the most distal point of central myelin is 3.1 mm. The thickness of glial sheath of proximal and distal segment is 50 µm, 5 µm respectively (original magnification ×10, ×40).

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