Continuing Education Activity

Microtia is a congenital ear deformity in which the external ear is malformed and underdeveloped. In more severe cases, it is usually associated with the absence of an ear canal, known as aural atresia. These patients suffer from severe conductive hearing loss in the affected ears. In the absence of a congenital syndrome, these patients generally live normal, full, and productive lives. This activity highlights the role of the interprofessional team in the evaluation and management of patients with microtia.

Objectives:

• Describe the Marx classification of ear microtia.

• Summarize psychosocial considerations for patients with microtia.

• Explain the different techniques of surgical microtia repair.

• Review the advantages and disadvantages of the various auricular reconstruction options.

Introduction

Microtia is a congenital hypoplastic malformation of the pinna that ranges in severity from a fully-formed auricle with slightly smaller subunits to complete absence of the auricle and lobule in its most severe form, known as anotia. The condition is often unilateral and creates an obvious asymmetry. It can be associated with many syndromes and is thought to be caused by vascular insults or different medications taken during embryologic development. Malformation or absence of the external ear can cause a conductive hearing loss on its own, but microtia is also often associated with aural atresia, a condition in which the middle ear and external auditory canal fail to form, substantially exacerbating the conductive hearing loss. There is often a correlation between the degree of auricular deformity and middle ear deformity. Careful collaboration between plastic surgeons and otologists is required when considering the timing of repair if these two conditions coexist.

Children born with craniofacial anomalies are at increased risk of low self-esteem and bullying.[1] Historically, attempts have been made to restore normal form and function by school age in order to prevent such social stigma. Treatment options include observation, treating the hearing loss component with devices such as bone-anchored hearing aids, applying a prosthetic ear for cosmetic improvement, and reconstructing the auricle with alloplastic implantation or costal cartilage autografting.[2][3][4][5] 

As operative techniques have evolved, particularly that of reconstruction with autologous costal cartilage, many surgeons have elected to postpone interventions until the patient reaches at least 10 years of age to ensure adequate costal cartilage stock for reconstruction as well as meaningful patient assent and participation in post-operative care. Children who undergo high-density porous polyethylene implantation are candidates at a younger age, typically three to five years old, but have a higher rate of infection and extrusion than those that undergo autologous costal cartilage implantation later.[6] Auricular reconstruction is challenging and is associated with several surgical complications; it should ideally be performed by teams with experience and high volume.

Etiology

Ear development is complex, with tissues originating from the neural crest as well as endoderm, mesoderm, and ectoderm layers to form the inner, middle, and external ear.[7] The outer ear develops from ectoderm and specifically arises from the first and second branchial (pharyngeal) arches, which form six hillocks of His at 6 weeks of gestational age. While authors have debated the exact contributions of the hillocks of his to the final form of the auricle, recent research suggests that the first branchial arch, (mandibular arch or Meckel's Cartilage) gives rise to hillocks 1-3 and forms the tragus (1), the helical crus (2), and the helix (3).  The antihelical crura (4), the antihelix (5), and the lobule and antitragus complex (6) are formed from the second branchial arch, also known as the hyoid arch or Reichert's cartilage.[8] 

Importantly, the stapedial artery also arises from the second branchial arch, and if it degenerates too early, microtia can result. Ultimately, these six hillocks fuse to form the auricle by 22 gestational weeks of age. The auricle develops to 85% of adult size by the age of 5 years and is fully developed by age 8. This early development is why some surgeons will elect to perform microtia reconstruction in very young patients, particularly if they are not using autologous rib grafting.   

While microtia may occur in isolation, it is sometimes associated with genetic craniofacial syndromes such as Goldenhar, Treacher Collins, Nager, Crouzon, and CHARGE syndromes, Pierre-Robin sequence, and others.[9][10][11] Teratogens, including isotretinoin, thalidomide, alcohol, and mycophenolate mofetil, when used during pregnancy or conception, can also result in microtia.[12][13][10] Other risk factors include first or high maternal parity, advanced maternal or paternal age, high altitude (above 8,200 feet), and low birth weight.[14][15]

Epidemiology

Microtia is usually unilateral (77% to 93%), more often right-sided (60%), and occurs more frequently in males (2.5:1). The prevalence per 10,000 births in the United States ranges from 1.8 to 3.5, and worldwide from 0.4 to 8.3. In the United States, there is a higher risk of microtia among Asians, Pacific Islanders, and Hispanic patients.[16]

History and Physical

The normal fully developed human ear is approximately 6 cm in height, sloped 20 degrees posteriorly from vertical, and has an auriculocephalic angle of 20 to 30 degrees with a 2 to 2.5 cm distance from the helical rim to the mastoid. Microtia is a condition in which there is an underdevelopment of the ear; in some cases, only a portion of the lobule and helix are evident. While examining patients, it is important to perform a complete head and neck examination to include evaluation of the mandible, the oral cavity and palate, the eyes, the function of the facial nerve, the color and quality of the skin, the level of the temporoparietal hairline, and the position of the auricular remnant. In some cases, microtia is associated with genetic syndromes, and therefore examination and notation of syndromic features should be documented as well as inspection for hemifacial microsomia, pre-auricular pits, accessory auricular appendages, and aural atresia. The auricular components of the ear should be examined and compared to the contralateral side.

Evaluation

Several grading systems exist for microtia, but the Marx classification is widely used. In this grading scale, a Grade I auricle is slightly smaller (at least 2 standard deviations below normal), but all subunits are present. Grade II: The auricle is smaller, and subunits are severely underdeveloped or absent; the upper half of the ear is often less developed than the lower half. Grade III: Only a small piece of cartilage is present in the superior remnant of the ear, and the lobule is rotated anterosuperiorly; this configuration is the most common and is often colloquially referred to as a "peanut ear." Grade IV: Complete absence of the auricle and lobule (anotia).  

Hearing should be assessed early in an infant with microtia or aural atresia. Auditory brainstem response testing should be performed. A moderate to severe 50 to 65 dB conductive hearing loss can result from unilateral aural atresia, although 10% to 15% may have simultaneous sensorineural hearing loss. It is equally important to test the non-atretic ear and not assume that hearing is normal.[17] A CT scan of the temporal bone is necessary to grade aural atresia and assess candidacy for repair using the Jahrsdoerfer criteria, but should not be performed until the child has reached an age of roughly 6 years, as atresia repair is not generally performed before that age and there are risks associated with exposing a younger child to the radiation of a CT scan.[18] 

There are 10 points in the Jahrsdoerfer grading scale, and patients with a score of seven or more should expect a better postoperative hearing outcome. A patient receives two points for the presence of a stapes and one point each for the following: malleus-incus complex, incus-stapes joint, patent oval window, patent round window, pneumatized middle ear, pneumatized mastoid, normal facial nerve, and normal external ear. A rating of 10 is excellent, 9 is very good, 8 is good, 7 is fair, 6 is marginal, and a score less than 6 is associated with poor candidacy for surgical repair.

Treatment / Management

Management of the microtic ear occurs along a spectrum, escalating from an observational approach to prosthetic ear placement to surgical reconstruction with a high-density porous polyethylene implant or autologous costal cartilage reconstruction. A minor abnormality of the auricle may not need correction, and intervention is typically sought by parents when there is a desire for cosmetic and functional improvements, such as wearing glasses or hearing aids. 

A prosthetic auricle is an excellent option and can be affixed to the head with adhesive or osteointegrated clips or magnets. A prosthetic specialist will match the skin color and appearance of the contralateral ear to design a realistic appearing prosthesis. Downsides include prohibitive cost and the risk of a young child losing the prosthesis accidentally. Patients with fair skin may require two prostheses, as their skin color changes between winter and summer months, and prosthetics will show wear and tear after a few years of use.

One method of surgical reconstruction is performed with a high-density porous polyethylene implant, a newer technique that is becoming more popular, largely due to the difficulty of achieving consistently excellent cosmetic results with autologous costal cartilage reconstruction.[5][19] With this method, a pedicled temporoparietal fascia (TPF) flap at least 11 cm wide by 12 cm high is harvested through an open scalp incision, a mastoid incision, or via an endoscopic technique. The flap is used to cover the entire implant with vascularized tissue and usually includes both the anterior and posterior branches of the superficial temporal artery. A drain placed under the implant provides suction and effectively shrink-wraps the TPF onto the implant, holding it in place and allowing the complex contours of the implant to remain visible. An anteriorly-based skin flap is raised to remove cartilage and skin from the ear remnant and cover the lateral surface of the auricle. Full-thickness skin grafting from the postauricular surface of the contralateral ear is often required to complete the coverage of the postauricular sulcus.[5] 

Advantages to this reconstruction method include reliably natural-appearing contours of the ear, no need for cartilage harvest (with the elimination of the risk of cartilage calcification and pneumothorax), and decreased operative time and patient morbidity. Potentially, the reconstructive surgery can be performed earlier, as there is no need to wait for costal cartilage maturation with this method.

Tanzer first described autologous rib cartilage grafting at Dartmouth in 1959, and subsequent differences in technique were then reported by Tanzer's pupil, Brent, and later by Satoru Nagata. The concept of the operation is consistent, however: an auricular framework is created from rib cartilage, which is shaped with scalpels, osteotomes, or biopsy punches, and then fixated together with permanent suture or steel wire. The construct is subsequently covered with overlying scalp tissue in a 2 to 4-staged surgical procedure. The differences lie in technique, laterality, and staging. Additionally, multiple donor sites are required during these complex procedures, including skin grafting from the groin, scalp, or contralateral ear, as well as the harvesting of costal cartilage.[6]  In Tanzer's original technique, his first stage transposed useable lobular tissue into a horizontal position and closed the resulting vertical defect. The wound was allowed to heal, and when the induration had softened, the fabrication and insertion of the costal cartilage framework, using the 6th to 8th ribs of the contralateral side, could proceed. The 6th and 7th ribs were used together at the synchondrosis, and the 8th was separated to form the helical rim. After careful preparation of the cartilage framework, it was positioned by re-excising and possibly extending the vertical scar from the first stage, and then covering it with skin and suturing it into place. The implanted cartilage was then left for 4 months to consolidate before elevating the construct in the third stage and then forming the tragus and conchal floor in stage 4, which were separated to diminish the risk of necrosis due to decreased blood supply to the ear.[2]

Brent's method differed slightly in that the first stage would include the harvest, carving, and placement of the cartilaginous framework in a subcutaneous pocket at the site of the microtic ear. The second stage would then include the transposition of the lobule, reversing the order of Tanzer's first two stages. His 3rd and 4th stages again elevated the construct and created a tragus while excavating the conchal bowl.[3]  

Nagata's technique is novel in that he performs his autologous ear reconstruction in only two stages. In his first stage, he harvests and implants the cartilage framework in a similar fashion to Tanzer and Brent; however, he simultaneously transposes the lobule and fashions the tragus in this stage because the tragus is part of the cartilaginous construct rather than a separate piece. Nagata's second stage elevates the construct and covers the exposed areas with a TPF flap and a skin graft. Another difference in technique is that Nagata harvests ipsilateral rib cartilage, rather than contralateral, as Brent and Tanzer described.[4] Further modifications of Nagata's two-step technique were described by Kurabayashi et al, in which a temporoparietal fascia pocket method was used, touted to be less invasive and more effective at creating a superior temporoauricular sulcus.[20] Fisher further modified Nagata's technique to create a single-staged procedure which has the advantage of avoiding a second surgery while maintaining favorable aesthetic standards.[21] 

When considering surgical repair, caution is warranted if the patient has had surgery or trauma to the area, as a robust blood supply is critical to avoid failure of the reconstruction. The surgeon should not feel pressured to perform the operation until the child is of an age when there is suitable costal cartilage available and sufficient patient motivation to participate in post-operative care. Patients with collagen or vascular diseases and those who may not tolerate long, staged surgical procedures are also not good candidates for autologous reconstruction and might be better candidates for prosthetic use.

Differential Diagnosis

Microtia is sometimes associated with congenital defects; therefore, syndromes such as Goldenhar, Treacher Collins, Melnick-Fraser, and others should be considered. Other common defects such as prominauris, cryptotia, cup or lop ear deformity, Stahl's ear, and lobule deformities may be mistaken for microtia, but may be treated effectively within three weeks of birth using an external ear molding system due to the flexibility imparted to neonatal auriclular cartilage by circulating maternal estrogens. Aural atresia is often associated with grade 3 and 4 microtia and should be evaluated.

Prognosis

Prognosis depends on the outcome measured and which treatment approach is selected. A bone-anchored hearing aid can be applied to overcome conductive hearing loss with great reliability and in some cases, a microtic auricle can be concealed with long hair. Similarly, the application of a prosthesis creates an ear that allows the patient to escape social scrutiny and can function to support glasses. In an article by Chunxiao et al regarding patient satisfaction after microtia reconstruction with autologous cartilage, patients were most satisfied with the helix and least satisfied with the tragus appearance.[22] The comparatively high rate of complications with autologous cartilage reconstruction, however, makes pre-operative counseling immensely important for expectation management and improved patient satisfaction. Most patients are ultimately satisfied with their reconstructed auricles though, especially because many feel that the construct becomes a part of them, in contrast to how patients often view auricular prostheses.[19][23]

Complications

In addition to the common risks of surgery to include pain, bleeding, swelling, infection, scarring, damage to surrounding structures, and the need for further surgery, complications of microtia repair include pneumothorax from costal cartilage harvest, infection of the cartilage (often with Pseudomonas aeruginosa), cartilage framework extrusion, changes in framework size, lobule necrosis, and migration of the construct from its original location.[24] Compression ischemia with loss of skin and TPF flap is also an early complication of porous polyethylene implantation.[19] Facial nerve injury can occur due to a lack of a predictable acatomical course in a maldeveloped ear, particularly when aural atresia repair is performed. Additionally, prosthetic ears are easily misplaced, and replacement is costly.  

Extrusion of the construct typically happens over the superior helical rim and is treated with temporoparietal fascia or occipitoparietal fascia flap coverage. This is the complication that requires the most frequent return to the operating room for repair because the superior helix tends to have the most tenuous blood supply on the reconstructed auricle.

Both costal cartilage constructs and porous polyethylene implants can migrate after placement, usually anteroinferiorly, although determining the correct location for initial placement can also be very challenging. Many cases of microtia are accompanied by hemifacial microsomia, which makes use of the normal side of the face as a template less helpful. While generally durable in the long-term, porous polyethylene has the potential to extrude or be infected with comparatively minor trauma compared to autologous cartilage constructs.[19] 

Lastly, most patients will have a low hairline on the microtic side; this can result in hair-bearing scalp covering the top of the reconstructed ear, which may later require removal with a laser.

Deterrence and Patient Education

It is critical to educate patients with microtia on the myriad treatment options available. Patients will need multidisciplinary care to include an otologist, plastic surgeon, audiologist, speech pathologist, and possibly an anaplastologist as well as a pediatrician if they have other associated syndromic complications. Discussion regarding the timing of interventions is crucial and the need for surgical intervention for comorbid conditions, such as aural atresia, must be taken into account.

Maternal prenatal counseling regarding the avoidance of teratogens should be performed as well.

Pearls and Other Issues

Microtia reconstruction is one of the most complex procedures in plastic surgery. It requires much experience in order to avoid the many potential complications of autologous cartilage reconstruction. Understanding the timing of the surgeries as well as collaboration between plastic and otologic surgeons is extremely important in order to produce consistently excellent results. Many of the principles discussed here are also applicable to auricular reconstruction for defects of other etiologies, particularly oncologic resection and avulsive trauma.

Enhancing Healthcare Team Outcomes

The most important consideration to improve outcomes in the treatment of a patient with microtia is early and clear communication between the surgeon and the family regarding the need for multidisciplinary care and the range and timing of interventions and management of any hearing loss. Primary care providers should be aggressive in treating infections of the contralateral normal ear, as patients may have associated conductive hearing loss in the microtic ear, and speech delays are more liable to occur in children with hearing loss. A good working relationship between the plastic surgeon and the otologist is also essential in order to coordinate staged repair of the microtic ear and any associated aural atresia.