MICROTIA REPAIR
SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds
DATE: May 1, 1996
RESIDENT PHYSICIAN: Ramtin Kassir
FACULTY: Karen A. Calhoun, M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.

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"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."

Embryology

The auricle and the external auditory canal are derived from the first and second branchial arches. These arches differentiate into the six auricular hillocks, three from the first arch and three from the second. By the sixth week of embryologic development, these hillocks have fused to form the auricle of the ear. Abnormalities in this developmental sequence result in deformities of the external ear. Microtia results when the deformed ear is too small. Various classification systems exist for microtia; the scheme described by Aguilar and Jahrsdoerfer include:

Grade I - normal ear

Grade II- some of the auricular framework is present, but there are obvious deformities

Grade III- peanut ear deformity, which encompasses anotia

Anatomy

In the adult the ideal auricle is approximately 5.5-7.5 cm high and about half as wide. It attaches on the lateral aspect of the head between horizontal lines drawn from the nasal spine and the superior aspect of the orbit. Normally the ear protrudes 30 degrees from the mastoid, and ideally inclines approximately 20 degrees posterior from the vertical.

The normal contours of the ear are created largely by the underlying elastic cartilage and include: helix - a ridge of cartilage that forms the superior and posterior rim of the auricle, and continues anteriorly as the crus of the helix and extends inferiorly to join the lobule antihelix- a Y shaped cartilage of major support that extends from the antitragus inferiorly, widening superiorly into a superior and inferior crus triangular fossa- the area formed between the inferior and superior antihelical crura scapha - the area formed posterior to the superior antihelical crus concha - the large central concavity of the lateral surface of the ear, bounded by the antitragus and the inferior crus of the antihelix. The helical crus divides the concha into a concha cymba superiorly and a concha cavum inferiorly.

Preoperative planning

Careful preoperative planning is essential in repair of microtia. Correction should usually begin at about age 6, especially for unilateral cases. At this age the child has not been exposed to cruel teasing and there is sufficient cartilage for framework fabrication. Furthermore, the child at this age is aware of the problem, wants it resolved, and is able to manage the necessary postoperative care. Forty five percent of patients in a series by Brent underwent reconstruction between the ages of five and seven. The size of the opposite normal ear can influence the timing of repair; if the other ear is large and the child is small, the surgery may have to be postponed for several years. Bilateral microtia and atresia cases may be started at an earlier age, but according to Brent beginning surgery prior to age 51/2 creates technical handicaps and poor patient cooperation.

Preoperative photographs are essential. In cases of microtia with atresia, radiologic exam (CT scan) prior to surgery provides useful information to the surgical team. To completely assess middle ear development, axial and coronal planes are necessary. If normal sensorineural function has been established preoperatively, the otologist can then assess middle and inner ear development and plan the third stage of the reconstruction. Auricular reconstruction is performed before the atresia repair as this ensures a virgin field without scars and compromised blood flow for the implanted auricular framework. Also, the cosmetic result is limited if the auricle has to be reconstructed around a bony canal drilled in the temporal bone.

Method of Repair

Autogenous cartilage is best since it has withstood the test of time. Irradiated cartilage reabsorbs; silastic tends to extrude with time and does not withstand trauma. In cases of congenital microtia and concomitant atresia, the surgical team should consist of the plastic surgeon and the otologist.

At birth the size of the ear is roughly 3/4 of normal and reaches full adult size by age 14. It has been shown by Tanzer that sculpted rib cartilage grows and keeps pace with the normal ear’s growth. Therefore it is not necessary to construct the graft any larger than the normal ear, rather, it should be made the same size or slightly smaller.

First Stage ( Framework fabrication and insertion)

A film pattern is traced from the normal ear and reversed to plan the new framework. In unilateral microtia, the position of the vestige from the lateral canthus is approximately the same as the normal ear’s helical root from the lateral canthus. If the patient has a low hairline, then it can either be adjusted after the reconstruction is completed or a smaller framework can be made and the opposite normal ear reduced.

When harvesting the rib cartilage, a chest incision is made on the side opposite the microtia. The first free floating rib is used for the helix and the synchondrosis of ribs 6 and 7 for the framework body. The framework is made slightly smaller (especially inferiorly) to accomodate the overlying skin and the future lobule. The triangular fossa and scapha are marked and carved using a No. 5 Paget gouge and a 15-C blade. All framework details are exaggerated, especially if the overlying skin is thick. The outer perichondrium on the framework body is preserved to allow nourishment from surrounding tissues. The outer perichondrium of the helical cartilage is trimmed to encourage warping in the proper direction. This is then sewed to the framework using mattress sutures of 4-0 nylon with the knots buried. A small preauricular incision is then made and the vestigial cartilage removed; the pocket is undermined to the extent that the framework may be inserted under tension free conditions. Brent advocates placing silicone drains beneath and posterior to the framework. Postoperatively, no pressure dressings are used and the drains are left in for 3-4 days.

Second Stage (Lobule transposition)

This stage involves lobule transposition and is performed several months after the framework is inserted. The lobule remnant is raised as an inferiorly based flap by incising around it; an incision is also made at the proposed superior inset margin. To avoid excessive protrusion of the lobule, the superior posterior incision on the back of the ear should be made fairly high. The vestigial tissue is excised from the fossa triangularis at this time. If no lobule exists, then one is created from the framework and defined later when the ear is lifted from the head.

Third Stage (Atresia repair)

Once normal sensorineural function has been established, the decision to operate depends primarily on the degree of middle ear development, as reflected by the size of the tympanum and status of the ossicles. The facial nerve usually has an anomolous course in aural atresia and it is monitored intraoperatively; failure to identify it clearly on CT preoperatively is not a contraindication to surgery. The ideal surgical candidate is one whose mastoid and middle ear size are at least two thirds of the normal size and if all three ossicles, although deformed, can be identified. Furthermore, CT should demonstrate the round and oval windows and a near normal or normal course of the facial nerve. Minimal criteria are presence of an ossicular mass and a middle ear of at least one-half normal size. Ideal candidates are selected for unilateral atresia cases; minimal criteria may be used in bilateral atresia cases.

The two basic techniques used are the mastoid and the anterior approach. In the mastoid approach, the sinodural angle is identified and followed to the antrum. The atretic bone is removed after the facial recess is opened and the I-S joint is separated. In the anterior approach, drilling is confined to an area bound by the TMJ anteriorly, the middle cranial fossa dura superiorly, and the mastoid air cells posteriorly. The problems of a large mastoid cavity are thus avoided and there is less surgical manipulation in the mastoid segment of the facial nerve. Once the atretic bone is removed, a fascia graft is placed over the mobilized ossicular chain. Hearing results are usually better if the chain is left intact instead of using interposition prostheses. A meatoplasty is then performed and aligned with the bony canal. Finally, the bony canal is skin grafted and stabilized with antibiotic impregnated gauze.

Stage four (Tragal reconstruction)

A composite chondrocutaneous graft is harvested from the normal ear’s conchal bowl and applied beneath a tragal flap developed by means of a J-shaped incision. The donor site is skin grafted if primary closure caused distortion of the normal ear. To accentuate conchal depth beneath the tragal flap, excess soft tissues in the bowl are excised.

Stage five (Auricular elevation)

An incision is made posterior to the auricular margin and the ear is elevated while preserving connective tissue on both the cartilaginous undersurface and the bony floor. The postauricular scalp is undermined and advanced to the sulcus to decrease the area to be skin grafted. These grafts are harvested from the lateral hip or buttocks areas and applied to the back of the ear and bolstered.

Complications

The most common complication that can occur from stage I is atelectasis. Pneumothorax, pneumomediastinum, pleural tear occur much less frequently. If the framework is inserted under tension, necrosis of the overlying skin can occur; hematoma and/or infection may lead to chondritis with subsequent graft loss. Furthermore, malposition of the framework may occur and the possibility of keloid formation always exists.

BIBLIOGRAPHY

Brent, B. Auricular Repair with Autogenous Rib Cartilage Grafts: Two Decades of Experience with 600 Cases. Plast. Reconstr. Surg. Sept 1992, 355-374.

Aguilar, EA III. Major Congenital Malformations of the Auricle. In Head and Neck Surgery-Otolaryngology, edited by Byron J. Bailey, pp 1535-41.

Lambert, PR. Congenital Aural Atresia. In Head and Neck Surgery-Otolaryngology, edited by Byron J. Bailey, pp 1579-1591.

Tanzer, RC. Microtia: A Long Term Follow-up of 44 Reconstructed Auricles. Plast. Reconstr. Surg. 61: 161, 1978.