Anatomy & Physiology

The anatomy of the middle ear cleft is extremely important in combined approach tympanoplasty. It relies on an accurate knowledge of the relationship between the facial nerve particularly in its vertical portion and the chorda tympani. Indeed it is the bony triangle between them that is drilled out in order to put into communication the mesotympanum and mastoid regions. It is referred to as the posterior tympanotomy. In all other respects the anatomy of the middle ear cleft is as for any other operation.

Indications

Indications for a combined approach tympanoplasty are as follows:

• Serous otitis media - rarely
• Grade III/IV retraction pockets
• Chronic suppurative otitis media: - Granulations, - Cholestetoma
• Placement of middle ear hearing aid
• Placement of cochlear implant

Anaesthetic

In this country there is a tendency to use general anaesthetic for the purposes of carrying out this surgery. However local anaesthetic techniques can be used along with patient sedation.

Technique

Incision
A post aural hairline incision is made from above the pinna to the level of the mastoid tip. The incision is deepened to the level of the temporalis fascia. The whole skin flap is then elevated anteriorly in this plane to the level of the external auditory canal but without entering it. A large anteriorly based Palva flap is raised from the mastoid bone to the level of the bony external auditory canal. It should be large enough to expose a finger breadth of bone superiorly to the external auditory canal and cleared inferiorly to the tip of the mastoid and the floor of the external auditory canal. A large temporalis fascia graft is harvested superiorly but leaving a band of temporalis fascia intact inferiorly. If necessary, conchal cartilage can also be harvested as can bone dust during the drilling phase of the procedure.

Procedure
An extended mastoidectomy is carried out with identification of the sigmoid sinus posteriorly, the middle fossa dura superiorly. The canal wall is kept intact. The mastoidectomy is extended as far forward as possible into the attic region in order to expose the region of the attic where the incus and malleus are found. The superior and posterior canal wall is thinned particularly medially. This aids in identification of the course of the chorda tympani. Great care is taken during the mastoidectomy to observe and find the main landmarks which are the lateral semicircular canal and short process of incus. The posterior tympanotomy is created using initially large cutting and then subsequently a large diamond burr until the facial nerve and chorda tympani have been identified in the vertical course.

Once identified progressively smaller diamond burrs are used to open up the triangle between the chorda tympani and facial nerve being careful not to disrupt or unduly move the incus with the drill.

The anterior tympanotomy is then performed by raising a tympanomeatal flap. The disease with or without appropriate ossicles, dependent upon the degree of destruction of the ossicles, is then removed from the mastoid through to the external auditory canal. It is desirable to remove it as an intact sac. In many cases there will have been loss of the bony wall posterosuperiorly particularly in the area of the scutum.

Once the disease has been completely removed, hopefully with preservation of the chorda tympani, if it is not completely involved in the disease, an endoscopic inspection of the cavity with particular reference to the attic and posterior tympanotomy is made. This is followed by an endoscopic examination via the anterior tympanotomy of the retrotympanum, the stapes footplate region, the protympanum and hypotympanum.

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