EXERCISE 14

ENDOSCOPIC DISSECTION OF APICAL TURN OF COCHLEA

The apical turn is smallest of the all turns situated infront of the second turn.
Its apex or copula is under the tensor canal and genu of the facial nerve.
Apical turn is only two thirds of the circle where the anterior widened part scala vestibuli ends as blind CUL-DE SAC.
The narrow part behind the HAMULUS ends at the scala tympani.

STEP A – EXPOSURE OF TERMINAL EDGE OF SPIRAL PARTITION
The modiolus has nothing to do with the frame work of the apex of the cochlea
At the top of the 2nd turn the modiolus ends, from the top of modiolus a ledge of bone extends to the top of apex in modiolar axis.
This is called THE TERMINAL EDGE OF SPIRAL PARTITION.
We can observe cul -de sac end of scala vestibuli, scala tympani, lax basilar membrane and terminal end of modiolus here.

STEP B – SCALA TYMPANI OF APICAL TURN.
Once the basilar membrane is removed we can see scala tympani below the scala vestibuli.
In apical turn the scala vestibuli is bigger than scala tympani.

STEP C – MAGNIFIED VIEW OF COCHLEAR APEX
The apex of the cochlea is seen clearly including osseus spiral lamina.

STEP D – HELICOTREMA.
At the top the two scalae are communicated with a small hole, It is HELICOTREMA.

STEP E – HAMULUS OR BEC OR ROSTRUM OR CROCHET
The osseus spiral lamina at the end of the apex end like a hook, It is Hamulus. Hamulus is free of all attachments

DEAR SURGEONS WITH MICROSCOPE WE CANNOT SEE ALL THESE DETAILS OF COCHLEA. ENDOSCOPES HELP US IN CLEAR VISUALISATION OF THESE STRUCTURES.
HENCE THE ENDOSCOPIC TEMPORAL BONE DISSECTIONS ARE NOW A DAYS VERY VALUABLE.

Labelling:
1 – Cul–de sac ending of scala vestibuli
2 – Scala vestibuli
3 – Basilar membrane of thr apical turn (width is lonest and lax)
4 – Temninal edge of the spiral partition
5 & 6 – Scala tympani
7 – Ending of modiolus
8 – Hamulus
C – Copula
M – Modiolus