Myringoplasty
By
Dr. T. Balasubramanian M.S. D.L.O.
Synonyms: Myringoplasty, Tympanoplasty.
Definition:
Myringoplasty is a procedure used to seal a perforated tympanic membrane
using a graft material.
Temporalis fascia is the commonly
used graft material because:
1. It is an autograft with excellent
chance of take
2. It is available close to the site of operation making
its harvest easier
3. It has a low basal metabolic rate, brightening
its success rate
4. Its thickness is more or less similar to that of
tympanic membrane
There are two available methods of performing
myringoplasty:
Overlay technique
Under lay technique
Overlay
technique: This is a difficult technique to master. Here the
graft material is inserted under the squamous (skinlayer) of the ear
drum. It is a difficult task peeling only the skin layer away from
the tympanic membrane, placing the graft over the perforation and
redraping the skin layer.
Underlay technique: This is a simpler
and commonly used technique. Here the graft is placed under the
tympano meatal flap which has been elevated hence the name under
lay. The major advantage of this procedure is that it is easy to
perform with a good success rate.
Indications of Myringoplasty:
1.
Central perforation which has been dry atleast for a period of 6
weeks.
2. As a follow up to mastoidectomy procedure to recreate the
hearing mechanism
Prerequisites for myringoplasty:
1. Central
perforation which has been dry for atleast 6 weeks
2. Normal middle ear
mucosa
3. Intact ossicular chain
4. Good cochlear
reserve
Procedure: Firstly a temporalis fascia of adequate site
must be harvested and allowed to dry.
The surgery is performed
under local anesthesia. Temporalis fascia graft is harvested under
local anesthesia conventionally and allowed to dry. The external
auditory canal is then anesthetised using 2 % xylocaine
mixed with 1 in 10,000 adrenaline injection. About 1/2 cc is
infiltrated at 3 - o clock, 6 - o clock, 9 - o clock, and 12 - o clock
positions about 3mm from the annulus. The patient is
premedicated with intramuscular injections of 1 ampule fortwin and 1
ampule phenergan.
Step I: Freshening the margins of
perforation - In this step the margins of the perforation
is freshened using a sickle knife of an angled pick. This
step is very important because it breaks the adhesions formed between the
squamous margin of the ear drum (outer layer) with that of the
middle ear mucosa. These adhesions if left undisturbed will hinder
the take up of the neo tympanic graft. This procedure will infact
widen the already present perforation. There is nothing to be
alarmed about it.
Step I: Freshening the margins of perforation -
In this step the margins of the perforation is freshened using a
sickle knife of an angled pick. This step is very important because
it breaks the adhesions formed between the squamous margin of
the ear drum (outer layer) with that of the middle ear mucosa. These
adhesions if left undisturbed will hinder the take up of the neo tympanic
graft. This procedure will infact widen the already present
perforation. There is nothing to be alarmed about
it.
Step II: This step is otherwise
known as elevation of tympano meatal flap. Using a drum knife a
curvilinear incision is made about 3 mm lateral to the annulus. This
incision ideally extends between the 12 - o clock, 3 - o clock, and 6 - o
clock positions in the left ear, and 12 - o clock, 9 - o clock and 6 - o
clock positions in the right ear. The skin is slowly elevated away
from the bone of the external canal. Pressure should be applied to
the bone while elevation. This serves two purposes:
1. It
prevents excessive bleeding
2. It prevents tearing of the flap
This
step ends when the skin flap is raised up to the level of the
annulus.
Step III: Elevation of the annulus
and incising the middle ear mucosa. In this step the annulus is
gradually lifted from its rim. As soon as the annulus is elevated a
sickle knife is used to incise the middle ear mucosal attachement with the
tympano meatal flap. This is a very important step because the inner
layer of the remnant ear drum is continuous with the middle ear
mucosa. As soon as the middle ear mucosa is raised, the flap is
pushed anteriorly till the handle of the malleus becomes
visible.
Step IV: Freeing the
tympano meatal flap from the handle of malleus. In
this step the tymano meatal flap is freed from the handle of malleus
by sharp dissection of the middle ear mucosa. Sometimes the
handle of the malleus may be turned inwards hitching against the
promontory. In this scenario, an attempt is made
to lateralise the handle of the malleus. If it is not
possible to lateralise the handle of the malleus, the small deviated tip
portion of the handle can be clipped. The handle of the
malleus is freshened and stripped of its mucosal covering.
Step V: Placement of graft (underlay technique). Now a
properly dried temporalis fascia graft of appropriate size is introduced
through the ear canal. The graft is gently pushed under the tympano
meatal flap which has been elevated. The graft is insinuated under
the handle of malleus. The tympano meatal flap is repositioned in
such a way that it covers the free edge of the graft which has been
introduced. Bits of gelfoam is placed around the edges of the raised
flap. One gel foam bit is placed over the sealed perforation.
This gelfoam has a specific role to play. Due to the suction
effect created it pulls the graft against the edges of the
perforation thus perventing medialisation of the graft
material.
.