title: Microanatomy and histological features of central myelin in the root exit zone of facial nerve.
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 µm (40-110 µm) at proximal REZ and 7.4 µm (5-10 µm) at distal REZ.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Neurosurgery, Gil Medical Center, Gachon University, Incheon, Korea.
authors.forename: Gi-Taek
authors.initials: GT
authors.lastname: Yee
authors.affiliation: Department of Neurosurgery, Gil Medical Center, Gachon University, Incheon, Korea.
authors.forename: Chan-Jong
authors.initials: CJ
authors.lastname: Yoo
authors.affiliation: Deparment of Neurosurgery, Ilsan Paik Hospital, College of Medicine, Inje University, Goyang, Korea.
authors.forename: Seong-Rok
authors.initials: SR
authors.lastname: Han
authors.affiliation: Deparment of Neurosurgery, Ilsan Paik Hospital, College of Medicine, Inje University, Goyang, Korea.
authors.forename: Chan-Young
authors.initials: CY
authors.lastname: Choi
keywords: Central myelin; Facial nerve; Glial sheath; REZ