EXERCISE 16

ENDOSCOPIC ENDOMEATAL DISSECTION OF INTERNAL CAROTID ARTERY.

The location of the internal carotid artery in the middle ear and in the petrous bone is very important for middle ear and lateral skull base surgeon.
In the middle ear the ICA is situated in the protympanum. Petrous carotid is extradural and intraosseus, extends from carotid foramen to upper border of petro lingual ligament.
Once ICA enters the petrous bone it presents short vertical couse, as turns infront of cochlea forms posterior bend.
From posterior bend the horizontal ICAstarts ,runs horizontally in antero medial direction.It is situated posterior to TT muscle, medial to eustachian tube, foramen of spinosum, ovale and at anterior border of trigeminal ganglion the petrous ICA turns above the foramen Lacerum, gives anterior genu.
From there it becomes verical. The paraclival ICA, at this level the vidian canal is lateral to F.Lacerum.

STEP A0 – THE POSITION OF ICA IN PROTYMPANUM.
Here the presence of trabiculae in protympanum indicates the ICA is little away from the cochlea, particularly in cellular mastoids.

STEP A – RELATION BETWEEN COCHLEA AND ICA.
The protympanum is drilled with diamond bur or piezo electric blade, the vertical ICA is skeletonized including its posterior genu. In cellular mastoids there is a space between ica and basal turn of cochlea, where as in contracted petrous bone the ICA hugs the cochlea.

STEP B – ICA AND JUGULAR BULB IN HYPOTYMPANUM.
The hypotympanum is drilled and carotid foramen anteriorly and jugular bulb posteriorly exposed THE CROTCH is seen between ICA and jugular bulb..it contains jocob nerve seen clearly here.

STEP C – COMPLETE EXPOSURE OF VERTICAL CAROTID.
Here the TM joint is completely exposed, and the ICA is exposed from carotid foramen to posterior genu From cervical portion the ica coming from anterior to posterior direction to enter carotid foramen .
It is noted here .The tympanic mouth of eustachian tube is seen. After posterior genu the ICA is directed anteromedially
A thin plate of bone seperates the ET to ICA The is a 1cm gap of bone seperates the tm joint to anterior part of verical carotid.

Labelling:
PT – Protympanum
1 – Crotch
2 – Eustachian tube opening
3 – Posterior genu
5 – Jocobsons nerve
6 – Carotid foramen
4 / 7 – jugular bulb
8 – Tm joint
10 – Bone between TM joint and vertical carotid canal.


With using 0 and 30-degree endoscopes, whole horizontal ICA can be exposed through open cavity mastoidectomy without giving external incisions, isolating facial nerve and lowering mandibular condyle. Here the only leading structure is eustachian tube
STEP F
DISSECTION OF DISTAL HORIZONTAL ICA…The horizontal ICA is followed distally by removing medial wall of the eustachian tube


STEP G
CARTILAGINOUS EUSTACHIAN TUBE AND ICA
The shepherd hook like cartilaginous et is identified. To its lateral hook, the tensor tympani muscle takes origin. Above the et is skull base and lateral to cartilaginous eustachian tube, the mandibular nerve and middle meningeal arteries are identified and dissected. The ICA is present medial to et


STEP H…
TRIGEMINAL GANGLION DISSECTION..once the skull base dura is identified above the eustachian tube, it is incised and trigeminal ganglion is identified.T he trigeminal ganglion passes above ICA medial to lateral and divides into 3 branches. The eustachian tube is dissected laterally enlarged. The enlarged eustachian tube leads to the nasopharynx
ET…Cartilaginous eustachian tube HICA…Horizontal ICA 1..ica 2…Trigeminal ganglion 3..naso pharync

ENDISCOPIC ENDOMEATAL DISSECTION OF INTERNAL CAROTID ARTERY

STEP CI – EXPOSURE OF CROTCH
Crotch is bony septum between carotid foramen (ICA) and jugular bulb.
Using 0 degree endoscope ICA and jugular bulb are exposed by drilling bone of floor of the hypotympanum.

STEP D – POSTERIOR GENU OF
ICA EXPOSURE
With diamond bur and gentle drilling of floor of tympanic mouth of estachian tube exposes the posterior genu of ICA.
Here the eustachian tubal opening is at the lateral side of ICA.
From posterior genu the horizontal ICA changes direction from postero lateral to antero medial

STEP E – EXPOSURE OF PROXIMAL HORIZONTAL PETROUS ICA.
To expose horizontal ICA canal wall down mastoidectomy is initial step. It allows wider dissection around ICA and surrounding areas .
Using 0 and 30 degrees endoscopes allows good view of ICA dissection.
Gentle drilling of medial wall of bony estachian tube visualises the ICA.
Removing lateral bony wall of estachian tube and widening the opening laterally gives more space.

Labelling:
ICA – Intrnal carotid artery.
C – Crotch.
JB – Jugularbulb.

ENDOSCOPIC ENDOMEATAL CAVERNOUS SINUS ICA DISSECTION (ENDOSCOPIC TYPE C ITF EXPOSURE OF ICA)

STEP H – TRIGEMINAL GANGLION EXPOSURE.
The trigeminal gaglion is exposed after dissecting bone of skull base and opening of dura

STEP A, B, C, D – ENDOSCOPIC EXPOSURE OF ICA IN CAVERNOUS SINUS.
The foramen Lacerum, anterior gennu, paraclival ICA and parasellar ICA are seen clearly

Pic H –
1 – Horizontal ICA
2 – Trigeminal ganglion
3 – Nasopharynx

Pic A and B –
1- Foramen lacerum
2 – Anterior genu
3 – paraclival ICA
4 – parasellar ICA

Pic C – CS – cavernous sinus

Pic D – PSC – parasellar ICA

Note: All the dissection pics are taken through endoscopic open cavity approach.