Pediatric Microtia Surgery 

Microtia is the most common major congenital anomaly of the external ear but is rare enough that parents usually have never encountered it. Because of the prominent location of the ears, any deformity is visible.

Health care providers may also be unfamiliar with this condition. Because of technical advances in the reconstruction of the microtic ear, results have dramatically improved in the hands of experienced ear reconstructive surgeons.

Because of the fine details of microtia reconstruction, the surgeon must have a complete understanding of the 3-dimensional form of the auricle and sound surgical principles of soft tissue management and transfer. The future of microtia surgery holds much promise.

This condition is rarely noticed prenatally and is very traumatic for parents. Another major stressor is the feeling of guilt that parents may experience. Reassure parents that they were likely not the cause of their child's condition.

The affected ear usually has severe conductive hearing loss (approximately 40-60 dB) secondary to lack of an external auditory canal and ossicular fixation. These children are likely to have normal speech.

Microtia is classified as follows based on a gradient from less severe (grade I) to total absence of the external ear (anotia):

Grade I

The pinna is malformed and smaller than normal. Most of the characteristics of the pinna, such as the helix, triangular fossa, and scaphae, are present with relatively good definition (see the image below).

Grade II

The pinna is smaller and less developed than in grade I. The helix may not be fully developed. The triangular fossa, scaphae, and antihelix have much less definition (see the image below).

Grade III

The pinna is essentially absent, except for a vertical sausage-shaped skin remnant. The superior aspect of this sausage-shaped skin remnant consists of underlying unorganized cartilage, and the inferior aspect of this remnant consists of a relatively well-formed lobule (see the image below).

Anotia

Total absence of the pinna is observed (see the image below).

Frequency

Microtia has been reported to occur in 1 per 6,000-12,000 births. Although the reason is unknown, microtia is seen more commonly in males than in females. In addition, the right side is affected more commonly than the left. Some studies have reported that the prevalence of auricular anomalies at birth increases with maternal age.

The actual cause is relatively unknown. McKenzie and Craig state that microtia may occur as a result of in utero tissue ischemia secondary to obliteration of the stapedial artery or actual hemorrhage into the local tissues.^[1]

Genetic studies have revealed several possible etiologic factors, such as chromosomal aberrations, multifactorial inheritance, and autosomal and recessive traits. The most common syndromes associated with microtia are Goldenhar syndrome and Treacher Collins syndrome.

In addition, several medications, such as thalidomide and isotretinoin (Accutane), have been implicated as causing severe congenital malformations such as microtia.

During the seventh week of gestation, the first and second arches give rise to 6 hillocks called the hillocks of His. The first 3 hillocks are derived from the first arch, and the final 3 hillocks are derived from the second arch. These hillocks then fuse, forming the future ear. The structures of the adult ear corresponding to the hillocks are the tragus (first hillock), helical crus (second hillock), the helix (third hillock), the antihelix (fourth and fifth hillocks), and the antitragus (sixth hillock).

Consultation regarding a patient born with microtia ideally should occur soon after birth. In addition to evaluation of the major organ systems, the initial hearing status of the child is of utmost importance.

Although severe conductive hearing loss results secondary to a malformed ear and absence or stenosis of the external auditory canal, inner ear function is almost always good, resulting in some ability to hear on the affected side.

The contralateral ear almost always is normal, resulting in relatively normal speech development. During the initial consultation, the ear reconstructive surgeon should reassure the parents and outline the future management of their child's condition.

If microtia is the only developmental anomaly, the initial workup consists of the evaluation of the child's hearing status. As previously stated, the inner ear function is usually normal in patients with microtia. Also, the middle ear status of the nonaffected ear is usually normal, resulting in overall normal hearing in the nonaffected ear. The contralateral ear is normal in most patients.

Unilateral microtia

Auricular reconstruction for unilateral microtia usually begins in children aged 6-8 years because the pinna reaches about 85-90% of its adult size at this age. By this time, the child is usually large enough that rib size is sufficient to harvest an adequate rib graft. If the child is still small, postpone surgery until an adequate rib for the framework can be harvested.

For example, if a very small 6-year-old child presents with microtia, postponing auricular reconstruction until age 7-8 years, when rib growth is sufficient, is reasonable. On the other hand, if a very large 5-year-old child presents with microtia, the surgeon may begin reconstruction sooner because of adequate rib size.

The ideal time to begin the reconstruction is the summer before the first grade. By the time the child starts the first grade, at least 2 of the surgeries can be performed, allowing the child to have the resemblance of an ear. Children tend to be teased during these early school years when the ear is not yet reconstructed.

Bilateral microtia

Surgical reconstruction in children with bilateral microtia is started at age 6-7 years, depending on their size. Before the pinna reconstructions, a CT scan of the temporal bones is obtained to evaluate for ear canal and middle ear reconstructive surgery. Two relatively smaller ears are not as noticeable as one asymmetric ear.

Starting the external ear reconstructions before the middle ear surgery is very important. If an attempt is made to open the canal before the external ear reconstruction, the elasticity of the "virgin" skin and the circulation are compromised.

Because these children are dependent on bone-conduction hearing aids, the goal of starting earlier is to finish at least one ear. The canal may be drilled soon after the ear is reconstructed. Obtaining adequate hearing without hearing aids is the eventual goal. If the child is not a candidate for atresia surgery, the bone-anchored hearing aid (BAHA) is also an option.

The reconstructive surgeon must intimately know the anatomy of the external, middle, and inner ear. Important landmarks include the helix, helical crus, antihelix, crura of the antihelix, tragus, antitragus, scapha, triangular fossa, concha cymba, concha cavum, and lobule.

The primary blood supply to the external ear is via the superficial temporal artery and branches of the posterior auricular artery. The sensory innervation of the external ear is via the anterior and posterior branches of the greater auricular nerve.

The location and reference point of the ear must be well understood. The angle of the long axis of the ear approximates the angle of the nasal dorsum. The superior point of the ear is usually at the eyebrow level. In a child aged 5-7 years, the helical crus is usually approximately 6.5-7 cm from the lateral canthus. The most inferior aspect of the lobule on the microtic ear is usually 0.5 cm higher than the normal side.

Contraindications to rib surgery for microtia reconstruction include high-risk surgical status and chest wall deformities. In addition, patients with pulmonary hypoplasia are at risk of a pneumothorax occurring during the rib harvest.