EXERCISE 8

ENDOSCOPIC ENDOMEATAL DECOMPRESSION OF LABYRINTHINE PART OF FACIAL NERVE

This is a very good exercise for residents.
Generally labyrinthine part of facial nerve can be decompressed by

A) Hearing preservation techniques:

  • Middle fossa approach

B) Hearing destruction techniques:

  • Translabrynthine (microsurgical)
  • Transcochlear or Transotic (microscopic or endoscopic) procedures

Endoscopically the complete decompression of facial nerve can be done from porus to stylomastiod foramen through the transmeatal approach by using 0 and 45 degrees endoscopes.

Endoscopically labyrinthine FN is divided in to
A – Perigeniculate portion
B – Perilabyrinthine portion
This part takes gentle concavity towards medially before entering IAC.
The pergeniculate part rests on roof of apical turn of cochlea and peri labyrinhine part rests on 2nd and basal turns of cochlea and passes in vestibulo cochlear groove in between cochlea and ampulla of superior semi circular canal.

Labelling:
TT – Tensor tunnel
TM – Tensor muscle
C – Cochlea
OW – Oval Window
HFN – Horizontal FN
C – Cochlea


ENDOSCOPIC ENDOMEATAL DECOMPRESSION OF LABYRINTHINE PART OF FACIAL NERVE

STEP D – REMOVAL OF TENSOR TYMPANI MUSCLE..
Once complete exposure of ICA is done and (not compulsary) the tensor muscle is cut and removed

STEP E – EXPOSURE OF GENICULATE GANGLION
The geniculate ganglion is completely exposed with piezo or with a bur, the wedge of bone between the genu and tensor canal is identified

STEP F – REMOVAL OF WEDGE
Removal of wedge of bone inferior to geniculate ganglion with adiamond bur and using 45 degree endoscope the first part of facial nerve is visualised from genu to meatal foramen
The fundus of IAC is deleniated by careful drilling.
The position of ICA, JUGULAR BULB, OVAL WINDOW and PETROUS APEX is noted endomeatally

STEP G – MAGNIFIED VIEW.. With using 45 degree endoscope the magnified view of labyrinthine facial nerve, fundus of ,oval window, sinus tympani and ampulla of posterior semi circular is observed.

Labelling:
TM -Tensor muscle
G – Geniculate ganglion
ICA – ICA vertical part(at the bend the ica is shrunken )
FN – Labyrinthine facial nerve
IAC – Fundus of ICA
MF – Meatal foramen
OW – Oval window
ST – Sinus tympani
APSC – Ampulla of posterior semicircular canal
C – Cochlear roof after drilling 


ENDOSCOPIC ENDOMEATAL DECOMPRESSION OF LABYRINTHINE PART OF FACIAL NERVE

STEP H – DISSECTION OF FUNDUS OF INTERNAL AUDITORY CANAL
With piezo careful dissection around fundus visualises meatal foramen, bills bar and transverse crest.

STEP I – MEATAL FORAMEN EXPOSURE.
Careful driling around fundus of ICA exposes meatal foramen It is present 2 mm antero superior to the fundus of meatus.
Meatal foramen is 0.58 mm in diameter situated between the junction of the perilabyrinthine part and internal auditory meatal part of the FN at the end of the gentle medial curvature of the labyrinthine FN

STEP J – EXPOSURE OF ROOF OF THE COCHLEA
The roof of the copula, first and second turns are exposed to visualize the the 1st part of fn The triangular space between the facial nerve and cochlear nerve is exposed .
The relation between facial, cochlear, superior and inferior nerves are observed.

STEP K – PERISIERS TRIANGLE
The perisiers triangle is triangular space between first and second parts of facial nerve Its apex is situated towards geniculate ganglion and base is towards vestibular window
The endoscopic endomeatal relation between oval window and internal auditory canal, sinus tympani and ampulla of posterior semicircular canal observed. The labyrinthine part of FN is divided in to perigeniculate and perilabyrinthine parts endoscopically and the perigeniculate part is straight and perilabyrinthine part is slight concave medially and finally it joins meatal part at meatal foramen
.

Labelling:
1 – Bills bar
2 – Transverse crest
MF – Mearal foramen
PL – perilabyrinthine segment of facial nerve
PG – Perigeniculate segment of facial nerve
G – Geniculate ganglion of FN 1st – Labirynthine FN
2nd – Horizontal FN
C – Roof of copula
1,11 – Roofs of 1st and 2nd nd turns of cochlea
SV – Superior vestibular nerve
IV – Inferior.vestibular nerve
C – cochlear nerve.
P – parisiers triangle
Ow – oval window
ST – Sinus tympani
APSL – Ampulla of posterior semi circular canal.