EXERCISE 10

ENDOSCOPIC ENDOMEATAL DISSECTION OF RETROTYMPANUM

Retrotympanum is posterior part of the middle ear cavity behind the annulus tympanicus.
The prominent reference point in retrotympanum is pyramidal process, with reference to pyramidal process and facial nerve the retrotympanum is divided in to 4 compartments:
2 medial and
2 lateral to facial nerve.
Very important part in retrotympanum is sinus tympani.
Sinus tympani is not seen with microscope due to deep recess particularly in type C.

STEP A – VISUALISATION OF THE RETROTYMPANUM.
Initially using 0 degree endoscope the retrotympanum is visualised.
Pyramidal process with pyramidal eminence, stapedial tendon, ponticulus, sibiculum and sinus tympani are visualised.

STEP B – Using 45 degree endoscope sitting infront of bone surgeon can visualise the retrotympanum very clearly.
In cases of deep sinus tympani partial curetting of pyramidal ridge including stapedius muscle clearly visualises sinus tympani

STEP C – VISUALISATION OF RETRO TYMPANIC STRUCTURES.
With the same position and using 45 degree endoscope all the structures of structures of retrotympanum including sinus tympani, ponticulus, stapes tendon, concomereta medialis, lateralis and fustis are obsreved

STEP C1 – DRILLING OF CONCOMERETA MEDIALIS AND SINUS TYMPANI AREA

Drilling concomereta medialis including inferior part of posterior lip of round window slowly with 2 mm bur exposes the singular nerve.
Singular nerve travels from outer surface of RWM just outside the scala tympani towards the ampulla of the posterior semi circular canal.

Labelling:
1 and ST – Stapes tendon
2 and ST..Sinus tympani
PE – Pyramidal eminence
P – Ponticulus
CM – Concomereta medialis
CL – Concomereta lateralis

EXERCISE 10 (Cont..)

ENDOSCOPIC ENDOMEATAL DISSECTION OF RETROTYMPANUM

STEP D – SINGULAL NEURECTOMY
Deep drilling in the area of concomereta medialis parellal to upper border of the fustis to wards the sinus tympani exposes the singular nerve.
This nerve is a branch of inferior vestibular nerve.
After its origin 2 mm medial to fundus of IAC, it passes through singular foramen, present at posterior wall of IAC to come out side of the round window to suply the ampulla of PSS.
Once the nerve is seen it is cut or avulsed using hook.

STEP E – EXPOSURE OF AMPULLA OF POSTERIOR SEMICIRCULAR CANAL
After removal of singular nerve
deeper drilling of bone with 2 mm endoscope near the floor of sinus tympani exposes the ampulla of PSS.

STEP F – BONY AND MEMBRANOUS AMPULLA OF PSS DRILLING.
Once the bony ampulla of PSS is skelotinized the membranous ampulla is visualises and it is removed to see ampullary lumen which opens in to postero inferior part of vestibule in posterior recess opposite to opening of crus commune.

STEP G – EXPOSURE OF INNER OPENING OF AMPULLA OF PSS.
The inner opening of the ampulla of PSS is exposed .
The apulla of PSS is opened in to postero inferior part of vestibule opposite to crus commune in posterior recess of the vestibule.
The relation between the amulla and sinus tympani is observed.

Labelling:
SN – Singular nerve
ST – Sinus tympani
FS – Facial sinus
APSC – Ampulla of posterior semicircular canal
FIAC – Fundus of IAC
C – Crus commune inner opening
V – Vestibule
AL – Ampulla of lateral semicircular canal
ML – Memranous labyrinth (membranous ampulla)
L – Lumen of ampulla of PSS