8Raising the Tympanomeatal Flap Safely

FWhat the flap is and why we raise it

Almost every middle-ear operation begins with the same manoeuvre: lifting the eardrum out of the way to see the ossicles behind it. The drum cannot simply be cut through, because it must survive intact to vibrate afterwards. Instead it is delivered forward as part of a tympanomeatal flap— a single sheet of posterior bony-canal skin in continuity with the tympanic membrane and its fibrous annulus. Raised off the bone and hinged anteriorly, the flap swings the drum forward like a trapdoor, opening the posterior middle ear while the membrane stays in one living piece [2023].

This is the access step on which the whole reconstruction depends. Whether the operation is an incus interposition, a partial or total prosthesis, or a stapes procedure, the surgeon must first see the incudostapedial joint, the stapes, the facial recess and the round-window niche, and that view is won by the flap. In a single-stage ossiculoplasty the flap is raised widely so the drum can be grafted at the same sitting; in a second-stage procedure on a healed drum, elevation is deliberately limited to the posterosuperior quadrant needed to reach the chain, preserving the drum’s attachment and tension [2003].

The flap is also a piece of living tissuethat must heal back down. It is not a window cut and discarded but a pedicled flap that keeps its blood supply, is laid back at the end of the case, and re-adheres to the canal over the following weeks. Everything about how it is designed and handled — the line of the incision, the plane of elevation, the gentleness of delivery — serves the twin goals of exposure now and healing later. The step-through below follows the flap from first incision to entering the cleft.

FDesigning the incisions: flap and vascular strip

There are two classic ways to cut the canal skin, and they suit different needs. The first is the tympanomeatal flap proper: two radial incisions in the posterior canal, joined by a curved incision running circumferentially a few millimetres lateral to the annulus. That distance is not arbitrary. Set the curve too close to the annulus and the flap is too short to peel and re-drape; set it too far back and the field is needlessly cramped and the pedicle overlong. A flap a few millimetres lateral gives length to work with while keeping the deep canal blood supply within the pedicle so the skin survives [2023].

The second design is the vascular strip, associated with lateral (overlay) grafting and wide canal work. Here two long radial incisions — classically near the tympanosquamous and tympanomastoid suture lines, around the 12 and 6 o’clock positions — isolate a posterior strip of canal skin that is everted out of the way, exposing the bony canal widely for drilling or a large graft. The strip is named for the supply it preserves: it is kept as a vascularised pedicle rather than excised.

A reasonable worry is that either incision might devascularise the canal skin and delay healing. Reassuringly, a stereological study comparing the two found that canal-skin revascularisation after the tympanomeatal flap and after the vascular strip was comparable, and both recovered a vascular density similar to non-operated controls — provided the pedicle is respected [2003]. The lesson is that incision design follows the exposure required — a focused posterior flap for limited access, a vascular strip for wide canalplasty or overlay grafting — while either heals well when its blood supply is preserved.

TElevating to the annulus and entering the cleft

Once incised, the flap is raised in the correct plane: subperiosteally, directly on the bone of the canal, lifting periosteum and skin together as one robust sheet. Stray superficial to that plane and the thin, fragile canal skin shreds; a torn flap heals poorly, granulates, and may retract. The elevator hugs the bone and the flap is peeled steadily medially towards the annulus, which is reached as a pale, slightly thickened ring sitting in the bony tympanic sulcus.

Delivering the annulus is the moment that demands the most finesse. The fibrous annulus is hooked out of its sulcuswith a fine instrument and the drum swung forward as a continuous sheet, opening the posterior mesotympanum. The commonest beginner’s error here is to lift too vigorously and avulse the drum from the malleus handle or tear a hole in a thin, atrophic membrane. The annulus is delivered, not yanked: gentle, patient traction lifts it cleanly out of the sulcus while the drum stays attached to the malleus. The relevant landmarks — the notch of Rivinus superiorly, the bony sulcus, and the relations of the chorda and ossicles — are worth rehearsing before the first cut [2016].

With the flap held forward by a self-retaining retractor or the speculum, the middle ear opens to view. In a wide, straight canal the microscope reaches this field directly; where an anterior bulge or a tortuous canal hides the deep recesses, the transcanal endoscope brings the lens to the lesion and lets the same flap be raised with even less bony removal, reaching the anterior annulus and retrotympanum that a microscopic view can miss [2016]. The circumference of the annulus is not uniform in what lies behind it; the risk map below shows where to be bold and where to be careful.

TProtecting the chorda tympani

The structure most reliably encountered — and most reliably injured — as the posterosuperior flap is raised is the chorda tympani. The nerve runs across the posterosuperior middle ear between the malleus handle and the long process of the incus, and it is frequently adherent to the deep surface of the flap and the annulus, so that it is delivered up with them as the drum is swung forward. It carries taste from the anterior two-thirds of the tongue, and dividing or even stretching it produces a metallic taste, numbness, or a persistently altered flavour that patients find genuinely troublesome.

The discipline is to recognise the chorda early and free it under direct vision. As soon as the pale cord is seen tenting across the field, the elevator’s tension is released and the nerve is dissected off the flap and annulus, then kept in view for the rest of the case. How much this matters is borne out by outcome data: across a systematic review of more than a thousand operated ears, a preserved chorda was symptomatic in about a quarter of patients, against roughly half when the nerve was stretched or sacrificed [2018]. Strikingly, a stretched nerve fares no better than a divided one — so a half-hearted attempt to preserve a chorda that is left under traction wins little.

Prospective work confirms both the frequency and the trajectory of the problem. In one cohort, taste disorders were reported by 42.7% at ten days, 23.3% at four months and 9.2% at one year, and where the chorda was healthy to begin with, transecting it caused more lasting disturbance than stretching it — the argument for preservation whenever the anatomy allows [2024]. When a chorda is hopelessly buried in cholesteatoma or so foreshortened that preservation would compromise disease clearance, a clean sharp division and honest counselling are preferable to leaving it stretched. The chart contrasts the three outcomes.

CHazards: the facial nerve and the anterior angle

Two less obvious hazards separate the safe flap from the dangerous one. The first is the tympanic segment of the facial nerve, which runs just above the oval window exactly where the deep posterosuperior flap is lifted. The bony canal over this segment is frequently dehiscent— histological and operative series put dehiscence over the tympanic segment in a large minority of ears, more so in chronically diseased and previously operated cavities [2014]. A flap densely scarred to a dehiscent nerve can be elevated straight onto it. The protection is to elevate the medial flap subperiosteally, slowly, under direct vision, to anticipate dehiscence in revision and canal-wall-down ears, and to identify the nerve by its landmarks before instrumenting near it rather than freeing scar by feel.

The second hazard is at the other end of the drum: the anterior tympanomeatal angle. The acute angle where the anterior drum meets the canal wall is the natural shape that keeps the membrane taut and efficient. Over-elevating anteriorly, lateralising the graft, or packing the angle carelessly fills in that acute angle — anterior blunting— which rounds off the drum, slackens it, and degrades hearing even when the chain is perfectly reconstructed [2003]. Many surgeons therefore deliberately limit anterior elevation, leaving the anterosuperior annulus undisturbed where access does not demand otherwise, and support rather than stuff the anterior recess when grafting.

CRe-draping and the result

Raising the flap is only half the job; laying it back welldecides whether the ear heals quietly. Once the reconstruction is done, the flap and drum are returned to their bed, the annulus is seated back into its sulcus, and the canal skin is smoothed flat against the bone with no curled, in-folded or overlapping edges — folded epithelium is how iatrogenic cholesteatoma pearls and pockets begin. The middle ear is supported from below with absorbable packing, and the flap is held down with a light canal pack until it re-adheres.

Holding the whole sequence in mind makes the flap a deliberate act rather than a reflex. The incision is designed for the exposure required and to keep the pedicle alive; elevation stays subperiosteal so the skin does not tear; the annulus is delivered, not avulsed; the chorda is identified and preserved; the facial nerve is anticipated where it may be dehiscent; the anterior angle is left unblunted; and the flap is re-drapedflat to heal. None of these steps guarantees a good hearing result on its own — that depends on the reconstruction and the middle-ear environment — but a torn drum, a stretched chorda, an injured facial nerve or a blunted angle each reliably spoils an otherwise sound operation. The safest entry is the one that leaves the next surgeon, and the patient, with as normal an ear as the disease allows [2023, 2016].