10Reconstructing Congenital Ossicular Anomalies

FThe puzzle behind a normal drum

Most ossiculoplasty repairs an ear that disease has damaged: a perforation, a cholesteatoma, a retraction that has eaten the long process of the incus. Congenital ossicular anomalies are a different proposition. Here the chain was built wrong from the start, while everything in front of it — the pinna, the canal, the eardrum — looks entirely normal. The child has simply never heard well on that side, and the otoscope offers no clue. The classic presentation is a non-progressive conductive hearing loss behind an intact, healthy drum in an ear that has never been infected or injured [1993].

These are the so-called minor anomalies— malformations confined to the middle ear, in contrast to the major anomalies of atresia and microtia where the canal and pinna are obviously deformed. Embryologically the ossicles arise from the first and second branchial arches, and the same developmental window that builds the malleus head and incus body from the first arch and the stapes superstructure from the second can go astray in characteristic ways. The result is one of a small repertoire of lesions: the stapes footplate fixed like a miniature congenital otosclerosis, the malleus and incus fused into a single block, the long process of the incus absentor replaced by a fibrous band, or — the most ominous — the oval or round window simply missing. The surgeon’s whole task is to work out which of these is present and whether it can be safely corrected.

FA surgical map: the Teunissen–Cremers classes

Because the repertoire of lesions is finite, it can be classified — and the most useful scheme is the one built explicitly around what the surgeon does next. Teunissen and Cremers, reviewing 144 operated ears, grouped congenital minor anomalies into four classes hinged on a single decisive variable: the state of the stapes footplate and the oval and round windows [1993]. It is a classification of operability as much as anatomy, because the footplate decides whether you are doing a stapes operation, an interposition, or nothing at all.

• Class 1 — isolated stapes ankylosis. The footplate is fixed but the malleus and incus are normal; functionally a congenital otosclerosis.
• Class 2 — stapes ankylosis with another ossicular anomaly. The footplate is fixed andthe chain above it is malformed (a fused malleus–incus mass, an absent long process, an epitympanic fixation).
• Class 3 — ossicular anomaly with a mobile footplate. The footplate (and usually the superstructure) move, but the conducting chain above is discontinuous or deformed.
• Class 4 — aplasia or severe dysplasia of the oval or round window. The window itself is missing or rudimentary, frequently with an aberrant facial nerve overlying the oval window niche.

The clinical power of this map is that prognosis falls steadily from class 1 to class 4. A fixed footplate with a normal chain above it is highly correctable; a missing window, with the facial nerve in the way, is the group where surgery most often fails or is best avoided altogether. Knowing the class before the knife is laid down shapes the consent, the chosen technique, and the honesty of the conversation about expected gain.

TReading the ear: audiology and imaging

The audiogram does the first triage. These ears show a conductive gap, often in the 30–45 dB range, that has been present and stable since childhood. A maximal gap approaching 50–60 dB hints at a fixed footplate and a discontinuity in series, the two lesions of class 2 adding their effects. Tympanometry is typically normal or shallow (an As-type trace with a fixed chain), and acoustic reflexes are absenton the affected side — a useful, easily overlooked sign that the chain is either fixed or broken.

Imaging is where trainees are most often misled. High-resolution CT of the temporal bone can beautifully demonstrate a fused malleus–incus mass, a foreshortened incus, an abnormal incudostapedial angle, or window aplasia with an aberrant facial nerve — and it is mandatory before surgery to look for the dangerous variants. But its sensitivity for the subtler lesions, above all an isolated footplate fixation, is limited. In a direct comparison of preoperative HRCT with surgical findings in 145 ears, only about 62% showed an anomaly on CT; nearly 38% read as completely normal yet were found at exploration to have stapes fixation or another minor anomaly [2020]. The lesson is blunt: a normal CT in a typical congenital conductive loss does not exclude a surgically correctable lesion. The diagnosis, in the end, is frequently made at the moment of exploratory tympanotomy, when the chain is palpated and the true class declared.

TMatching the repair to the lesion

Reconstruction follows directly from the class, and the governing question at tympanotomy is always the same: what is fixed, and what is discontinuous? Palpate the chain. If the malleus and incus move freely but the stapes will not, the obstruction is the footplate. If the upper chain is loose and the footplate rocks, the problem is a break in continuity.

Two cautions deserve emphasis. First, when the malleus and incus are fused but mobileand the footplate is fixed, the fused mass is itself a perfectly good sound-conductor — the lesion is the footplate, and the correct move is a stapedotomy to the vestibule, not the removal of the conducting mass. Sacrificing a mobile columella to chase a fixed footplate is a classic error. Second, congenital footplate fixation should be addressed by a controlled small-fenestra stapedotomy rather than by blind mobilisation, which frequently refixes and risks a floating footplate; the principles mirror stapes surgery for otosclerosis, with the same respect for the vestibule[2011]. In children with a mobile footplate and a deficient chain, series using interposition grafts, Teflon pistons and partial or total prostheses confirm that these ears can be reconstructed to good effect [2016].

CHearing results and the hidden inner ear

How much hearing can be returned depends overwhelmingly on the class. Isolated footplate fixation does best. In a consecutive series of 39 ears treated by stapedotomy for isolated congenital stapes ankylosis, the mean air-conduction threshold improved by 21 dB and the air-bone gap closed to within 20 dB in 74% of ears, with results stable over time[2011]. Add a second lesion and the figures soften: across 23 ears with a mobile footplate but a malformed chain, the mean postoperative air-bone gap was around 19 dB[2012]. A mixed surgical cohort closing to within 20 dB in 44% — with isolated stapes fixation again the best-performing subgroup — rounds out the same message: the simpler the lesion, the better the ear hears afterwards [2021].

There is a second, quieter reason these results trail behind acquired ossiculoplasty: the inner ear is often not entirely normal. Many congenitally malformed ears carry a degree of coexisting sensorineural impairment, typically 10–20 dB, that the bone- conduction line conceals only partially and that the surgeon cannot improve. Closing the conductive gap perfectly still leaves the patient short of the cochlea’s own ceiling[2011]. This is why the honest counselling figure is the achievablehearing level, not merely the gap closed, and why a careful preoperative search for an accompanying sensorineural component — and for a syndromic diagnosis — matters as much as the planned mechanics.

CCounselling, timing and the unilateral ear

The hardest decisions in this field are not technical but strategic, and they turn on whether the loss is one-sided or both. A bilateral congenital conductive loss is genuinely disabling; reconstructing the better-prognosis ear (or fitting amplification) is clearly worthwhile and is usually undertaken once the child is old enough for reliable audiometry and a co-operative examination. A unilateralloss with a normal contralateral ear is a different calculus altogether: the child hears, develops speech and language normally, and the operation is then a discretionary attempt to restore binaural hearing in an ear that carries a real, if small, risk of sensorineural injury or facial-nerve trouble — the latter especially in the window-aplasia group, where an aberrant nerve crosses the very target of surgery.

That risk profile is precisely why the class 4 ear is so often left alone. When the oval window is aplastic and the facial nerve overlies the niche, the chance of a useful hearing gain is low and the chance of harm is not, so a bone-conduction device or contralateral- routing aid is frequently the wiser path. The unifying principle across all four classes is the same one that governs the whole atlas: define the lesion before you commit to a reconstruction. A surgeon who has palpated the chain, identified the fixed and the discontinuous element, and matched the repair to the Teunissen–Cremers class — doing a stapedotomy for a fixed footplate, an interposition for a broken chain, and exercising restraint for an absent window — will give the patient both the best hearing and the most honest expectation [1993, 1990].