EXERCISE 15

ENDOSCOPIC DISSECTION OF THE VESTIBULE

VESTIBULE AND STAPEDOTOMY SURGEON

Stapedotomy is a very common operation now a days. The stapes surgeons are very familiar with the anatomy of the vestibule. Now a days endoscopic anatomy gives more details of the vestibule particularly the medial wall and its structures By knowing the inside structures and their relationship with stapes the surgeon is sure to put the piston in the correct position

STEP A – VESTIBULE
Human vestibule is 5 mm × 5 mm bony box with 6 walls The anterior half of the lateral wall is formed by oval window.
The posterior half of the lateral wall is near the sinus tympani (2 to 3 mm) The thin bony wall seperates the pyramidal process, sinus tympan to the vestibule.

STEP C – SACCULE AND STAPES STAPES IS REFERENCE POINT OF VESTIBULAR ENDOSCOPY.
The saccule is situated opposite to anterior three-fourths of stapes in the spherical recess where as utricle is situated above the saccule and both are separated by crista vestibularis.
The utricle is present medial to the horizontal facial nerve. The medialsurface of stapes directly related to saccule. Remember the anterior edge (anterior commissure) of oval window is very close to the saccule.

SURGICAL IMPORTANCE:
1) There are perilymphatic fibres connecting anterior part of foot plate to saccule so in case total stapedectomy removal of total foot plate pulls and injures the scaaule
2 ) Out of whole foot plate the anterior end of foot plate is very near to saccule (the saccule extends over the anterior wall of the vestibule)
Hence during stapedectomy with sulaxation of footplate (if the anterior end luxates inside vestibule) it injures saccule..

3) The anterior part of foot plate is nearer to saccule than the posterior part

Labelling:
Dotted lines – position of vestibule over medial wall of the middle ear
S / 10 – saccule
U – utricle
SV / 9 – Scala vestibuli
ST / 11 – Scala tympani
VC – Vestibular crest (crista vestibularis)
HFN – Horizontal facial nerve
CP – Cochleariform process
A – Anterior
P – Posterior
The blue dotted line in live indicates the posterior limit of saccule in relation to stapes (The posterior third of stapes is free from saccule).


ENDOSCOPIC DISSECTION OF VESTIBULAR CREST (CRISTA VESTIBULARIS)AND UTRICLE


The anatomy particularly the medial wall of the vestibule is very important for the stapes surgeon. The endoscopy gives more details of the medial wall
CRISTA VESTIBULARIS..is a semi circumference bony ledge on the medial wall of the vestibule. It has two parts.1 horizontal portion ..present horizontally in anteriorly separates saccule below to utricle above.

LINE OF 3 RIDGES(GURRIER)Lower border of the horizontal facial nerve, horizontal crista vestibularis and falciform crest of the fundus of Iac are at same level.1. The vertical part of vestibular crest .it separates cochlear fossa posteriorly to saccule anteriorly


STEP A…EXPOSURE OF UTRICLE. Utricle occupies the superior third of medial wall of vestibule medial to horizontal fn. Its long axis is placed horizontally. It is separated from saccule inferiorly by vestibular crest.we can see parts of vestibular crest here clearly


SURGICAL IMPORTANCE

utricle is related to the upper border of the footplate of stapes only and the major part of the footplate is in relation with saccule.


STEP B ..PYRAMID OF VESTIBULE. It is a triangular bony crest at an anterior part of crista vestibularis. it contains terminal branches of utricular nerve(branches of superior vestibular nerve) to supply utricle. COCHLEARFOSSA is semioval fossa behind the vestibular crest contains ductus reunions. Utricle is horizontally placed looks like a banana-shaped membranous structure


SURGICAL IMPORTANCE

If the piston is placed too inferior and posteriorly in stapes surgery, it injures ductus reunions
STEP C ..VISUALISATION OF SULCIFORM GUTTER. Endiscopically this gutter is clearly visible present just behind the utricle from there the endolymphatic duct arises inside the vestibule


STEP D.VISUALISATION OF MACULA OF UTRICLE…In live surgeon can observe horizontally placed white structure under the HFN. It is macula of utricle .so macula of utricle is horizontally placed where as the macula of saccule is vertically placed parts.

The pinch point here is the safe position of placement of piston in stapes surgery. The depth here is the deep This point is present inferior to the center of the long axis of foot plate and just posterior to center


SURGICAL IMPORTANCE

If the piston is placed too high near the lower edge of HFN it rubs the macula and injures the utricle surgeon can observe this point here