Microtia

Frequency

Melnick and Myranthopoulos reviewed auricular deformities and associated anomalies in a series of 56,000 pregnancies in an ethnically diverse population (Caucasian 46%, African American 46%, Latino 8%), commenting on the incidence of anomalies and the embryogenesis and etiopathology of the varying deformities. ^[3] Ear deformities occurred in approximately 1.1% (11 in 1000) of births. Severe anomalies, such as microtia, occurred in approximately 3 in 10,000 live births. Occurrence has been reported to be 1 in 4000 in the Japanese population and as high as 1 in 900 to 1 in 1200 in the Navajo population.

Almost one half of the microtia patients in the Melnick and Myranthopoulos study (9/16) presented with craniofacial microsomia, also known as facial-auricular-vertebral syndrome. In the same study, the right side was affected almost twice as often as the left, and bilateral deformity occurred in 10% of patients, with the reported ratio of right-to-left-to-bilateral of approximately 5:3:1. Many sources report that vertebral, urogenital, and renal anomalies occur within the craniofacial microsomia syndrome, although this was not confirmed in this cohort.

Both hereditary factors and vascular accidents in utero have been suggested as factors in the etiology of microtia. Several groups have studied their microtia patients as probands, finding evidence for familial craniofacial microsomia and patterns suggestive of multifactorial inheritance.

Specific causative factors also can include maternal rubella during the first trimester of pregnancy; Brent has reported thalidomide exposure during pregnancy as a cause. ^[4] Poswillo points to the varied timing of teratogenic insults in patients with ear deformities associated with mandibulofacial dysostosis (Treacher Collins-Franceschetti syndrome) and more common forms of branchial arch anomalies in hemifacial microsomia. ^[5]

A report by Ryan et al using the National Birth Defects Prevention Study indicated that risk factors for anotia/microtia also include male gender, multifetal pregnancy, parents of Hispanic ethnicity or of non-US birth, maternal obesity, and prepregnancy diabetes. The likelihood of the condition was lower in children of black mothers or mothers who reported taking daily supplements containing folic acid. ^[6]

Embryology

A review of embryology allows a better understanding of the pathophysiology of microtia. The anatomy of the microtic ear is similar to the anlage seen in the 6-week embryo. Microtia often is associated with atresia or absence of the external auditory meatus, suggesting an arrest of development.

The external and middle ear develop from the first (mandibular) and second (hyoid) branchial arches. The auricle begins development at 5 weeks from 6 hillocks, 3 on either side of the first branchial cleft between these 2 arches, which becomes the external canal. Ultimately, the hillocks of the first arch contribute to the tragus and the root of the helix, and the remainder of the auricle develops from the hillocks of the second arch. The middle ear ossicles develop from the first and second arch with the mastoid air cells, eustachian tube, and remaining middle ear developing from the first pharyngeal pouch. The tympanic membrane develops where the first pouch meets the first cleft.

Initially, the ear has a ventromedial position, which becomes more dorsolateral as the midface and mandibular processes grow and push it outward and upward. Interruption in the proliferation or fusion of the hillocks at varying stages of development can produce the variable rudimentary structures that present as microtia.

Pathophysiology

Microtia has been divided into two descriptive categories. More frequently, the lobular type presents as a soft tissue mass without any concha or auditory meatus formation within the cartilage remnant. See the image below.

Less often, the conchal remnant type presents with more recognizable portions of a conchal bowl, tragus, and external meatus. See the image below.

In most patients with isolated microtia, the ear remnant is positioned with relative symmetry or somewhat superiorly to the contralateral ear.

The descriptive term auricular dystopia has been applied in cases associated with significant craniofacial microsomia. See the image below.

The mandible, maxilla, facial musculature, and facial nerve, which also are derived from the same branchial arches, are affected in patients with craniofacial microsomia and microtia. Some consider isolated microtia to be a mild expression of the continuum of craniofacial microsomia. In auricular dystopia, the microtic ear is placed inferiorly and anteriorly compared to the unaffected side. The underlying bony hypoplasia of the temporal bone and mandible exacerbate this situation, presenting a further challenge to the reconstructive surgeon.

Because the inner (neural) portion of the ear develops on a different time scale and from different ectodermal tissue, most patients have some hearing in the affected ear. In the case of bilateral microsomia, acceptable hearing can be achieved with bone conduction hearing aids and eventual canal, ossicular chain, and tympanic reconstruction. Typically, auditory surgery is performed after auricle reconstruction. Many patients with unilateral defects and normal hearing on the unaffected side do not pursue middle ear and canal reconstruction. Insufficient improvement on the affected side with the surgical technology currently available still leaves the patient effectively monaural.

As previously stated, many sources have reported that vertebral, urogenital, and renal anomalies occur within the craniofacial microsomia syndrome. Moreover, a retrospective study by Kini et al found a significant risk of structural renal abnormalities in children with microtia. Of 98 pediatric patients with microtia who underwent renal ultrasonography, 24% were identified as having a structural abnormality such as pelviectasis, renal ectopia, a duplicated collecting system, or renal agenesis. These abnormalities were seen in 43% of syndromic children and 21% of nonsyndromic patients. ^[7]

Most patients present as infants or children. The head and neck examination should be complete; search for other evidence of craniofacial microsomia including facial asymmetry, epibulbar dermoids, malocclusion, facial nerve weakness, and macrostomia.

Consultation with a geneticist is often helpful to identify special subsets of microtia patients, such as those with Goldenhar syndrome. Genetic consultation is also helpful to the family to identify risk to future progeny of the parents and of the proband.

Using three-dimensional (3-D) chest computed tomography (CT) scanning, a study by Wu et al found a high incidence of congenital thoracic deformities in patients with microtia. The study included 239 patients with microtia, 68 of whom (28.5%) were found to have thoracic deformities, including rib and/or spinal deformities. The incidence was highest in cases involving a more serious grade of microtia. ^[8]

Both functional and psychological considerations enter into the decision to correct microtia. Functionally, without the presence of an auricle and its postauricular sulcus, the patient's ability to wear glasses and hearing aids is impaired. Psychologically, the absence of an ear is significant for both males and females. Even after adjusting hairstyles, the absence of an ear is noticeable to peers and others. Like other patients with blatant anomalies, many children with microtia have lower self-esteem and develop either behavioral problems or become excessively introverted.

Timing of reconstruction presents some relative contraindications. In the United States, most of the presenting patients are children although many untreated adults are seeking reconstruction. For symmetric reconstruction, a good estimate of the size and position of the contralateral ear must be made. See the image below.

The ear reaches approximately 85% of adult size at age 3 years. Growth continues into adulthood but little change in the width or distance from the scalp occurs in individuals older than 10 years. For practical purposes, the normal ear is developed fully by age 6-7 years. To perform an autologous reconstruction, sufficient cartilage must be available. Generally, the costal cartilages are adequate by the time the patient is aged 10 years. The surgeon must balance concerns regarding the psychological impact of the deformity with having sufficient cartilage to carry out the optimal reconstruction in the fewest number of surgeries.

Optimal reconstruction requires costal cartilage of sufficient size and shape to carve the key framework details and maintain the strength to display these details through the overlying skin envelope. While some surgeons begin the reconstruction when patients are aged as young as 5-6 years, clearly better results can be obtained if the reconstruction is performed when patients are aged 9-10 years or older.

Clearly, the potential psychological issues of the child dealing with his or her deformity need to be balanced with the benefits of delaying the surgery for a few more years. As surgeons who have gradually made the transition of performing reconstruction at the lower end of that spectrum to feeling strongly that the surgery is better delayed, the authors think most children deal with the delay of the reconstruction without ill effects. Parents must be told that the best chance for an ideal reconstruction is the first attempt, even if this means delaying the surgery for a few years. They should be reminded that once the reconstruction is complete, children benefit from the improved outcome for the rest of their lives.

Opinions vary between surgeons as to the optimal sequence of procedures for reconstruction of the microtic ear. While the approach championed by Dr. Brent is well illustrated in the literature, ^[4] with excellent long term results, newer approaches by Drs. Nagata ^[9] and Firmin ^[10] have been followed by others, with possibly better results. The basic steps required are similar, but the staging and manner in which those steps are accomplished vary. While the senior author has adopted an approach closer to the latter, we will comment about the former as well.

The reconstruction of microtia, regardless of the type and associated deformities, requires 2 main elements. The first is sculpture of a framework from autogenous rib cartilage to reproduce the contours of the ear, and the second is coverage of the framework with the cutaneous remnant and adjacent skin. The greater part, if not the complete reconstruction, can be accomplished in 2 stages, with only minor revisions generally required beyond these 2 surgeries. Key to all reconstruction is the proper planning, and, ultimately, positioning of the reconstructed ear. This is even more critical in cases in which more significant facial hypoplasia is associated with the ear deformity.

The external ear consists of an elegant, 3-dimensional cartilage framework with a soft tissue lobule. An intricate terminology has developed to describe the convolutions of the auricle and is best reviewed visually.

The skin on the anterior surface is densely adherent and sebaceous. The skin on the posterior or cranial aspect is applied more loosely and is generally glabrous. Dividing the structure into 3 levels or complexes helps to analyze the components necessary for recreating it; the most cranial level is the conchal bowl complex, followed by the antihelical-antitragal complex and finally, the helical rim-lobule complex.

The proportions and relative position of the ear to the face, jaw, and scalp are important in planning its reconstruction. They have been recited in multiple texts and are summarized best by Tolleth. ^[11]

The height of the ear is approximately equal to its distance from the lateral brow at the level of the helical root. Its width is approximately 55% of its height. Its top aligns with the brow, and the lobular tip aligns with the columella. The mature ear typically is 5-6 cm long. The helical rim protrudes approximately 2 cm from the skull at an angle of 21-25°. The long axis of the ear does not parallel the nasal dorsum but is approximately 15-20° posteriorly rotated from the perpendicular axis of the body.

The blood supply to the external ear is from the postauricular artery, with minor contributions from branches of the superficial temporal artery. Venous egress is via the postauricular veins into the external jugular system. Lymphatic drainage follows the embryology with the derivatives of the first arch draining through the parotid nodes and the second arch derivatives through the cervical nodes.

The external ear is innervated by the great auricular nerve (C2-C3), the auriculotemporal nerve (V3), the lesser occipital nerve, and the auricular branch of the vagus nerve (Arnold nerve).

A study by Otto et al of patients with lobular-type microtia indicated that the affected ear has less than half of the available skin surface area that a healthy ear has. Imaging plaster ear models with a microcomputed tomography scanner or a cone-beam computed tomography (CT) scanner, and then converting the images into mesh models, the investigators determined that healthy, adult-sized ears in the study had a mean total skin area of 47.3 cm², compared with an average of 14.5 cm² for ears with microtia. ^[12]

The only absolute contraindication to ear reconstruction is a health condition preventing the patient from undergoing a series of 2-3 surgeries under general anesthesia. The remaining contraindications to ear reconstruction are relative.

As in all plastic surgery, the outcome of surgery depends on patient selection. Relative contraindications to surgery include lack of family support, inability to follow through with surgical care, and unwillingness of the child.