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Surgery for Congenital Ear Malformations
Robert A. Jahrsdoerfer Bradley W. Kesser
Congenital malformations of the ear can be broadly classified into two categories:
- Minor malformations Problem is limited to the middle ear
- Major malformations Atresia or stenosis of the external ear canal. Congenital aural atresia means the external ear canal has failed to develop. Congenital stenosis refers to partial development of the external ear canal. Both are usually associated with microtia, although on occasion the external ear may be well formed.
- Auditory brainstem response (ABR) testing is mandated in a newborn with microtia/atresia. Otoacoustic emissions may be of use in unilateral atresia if the contralateral ear is normal.
- The side with the better cochlear reserve is operated upon to achieve the best postoperative hearing result.
- If there is any doubt concerning hearing, a bone conduction hearing aid should be placed as early as possible.
- Audiologic testing should be repeated prior to surgery.
- A high-resolution computed tomography (CT) scan of the temporal bone in the 30-degree axial and 105-degree coronal planes should be obtained. The appearance of the CT scan will be the primary determinant of the patient’s candidacy for atresia surgery. The scan is again reviewed on the day of surgery with emphasis placed on the course of the facial nerve, slope of the tegmen, and depth of the middle ear from the lateral aspect of the skull.
- Minor malformations typically involve the stapes/oval window/facial nerve axis. The auricle and external ear canal are normal in appearance, or almost so, and the tympanic membrane can be identified.
- When an absent oval window is found at surgery, the choices available to the surgeon are to terminate the operation or to attempt hearing restoration by creating a vestibulotomy. If the latter approach is chosen, there should be a defined oval window area that can then be targeted for drilling, as well as mature ossicular development to enable placement of a prosthesis.
- Once a vestibulotomy is drilled, the opening should be covered with temporalis fascia or other appropriate soft tissue seal. The distance between the new oval window and the ossicle may vary greatly. A wide assortment of prosthesis lengths should be available.
- A bare facial nerve will not infrequently be found to overlie the area where the new oval window should be drilled. In malformations limited to the middle ear, it is not possible to transpose the facial nerve as it is in atresia surgery. A decision must be made to drill above or below the bare facial nerve. Again, a well-defined oval window area helps in this decision. Lacking this, drilling may begin superior to the nerve using a saucerizing technique. If the vestibule is not encountered at a depth of 2 mm, the procedure is terminated because there is a heightened risk of sensorineural hearing loss from surgical violation of the membranous labyrinth.
- If a bare facial nerve obscures the oval window superiorly, a promontorial window may be drilled according to Plester.1 The promontorial bone should be saucerized down to an intact endosteal membrane. Disruption of the endosteal membrane carries a greater chance of nerve loss from cochlear injury. A prosthesis can be inserted between the endosteal membrane and the malleus handle, or the tympanic membrane if the handle is unfavorable.
- The most important aspect in exploring the middle ear of a patient with a conductive hearing loss is an awareness that one may be dealing with a congenital malformation. This awareness must include the possibility of finding a bare and displaced facial nerve. Failure to recognize this possibility places the patient at a huge risk of facial nerve injury.
- Congenital primary incus fixation is rare. Fixation of the malleus in the epitympanum is not. There are two surgical methods to correct malleus head fixation:
- Remove the malleus head and incus, and place an incus strut from the malleus handle to the stapes.
- Drill away the bony attachment in the epitympanum, and interpose Silastic® sheeting as a barrier to bony refixation.
- Ossicular fixation may also be attributable to a malleus bar. This is a term coined by Nomura2 to describe a bar of bone running from the malleus neck to the posterior bony annulus. This bony bar will be ~1 mm in thickness and firmly fixes the malleus in place, producing a conductive hearing loss. The chorda tympani nerve frequently runs in a bony groove in the bar and must be considered when drilling away the bar. Freeing the ossicular chain from the malleus bar will usually correct the conductive hearing loss, but not always. If the chain remains fixed, one must search for additional sites of fixation. It is our preference that any suspected congenital middle ear malformation be approached through a postauricular incision. The ossicular anomaly, commonly the stapes/oval window/facial nerve complex, is often concealed by overhanging bone. As much as 3 to 4 mm of bony overhang may need to be drilled away to access the area of concern.
