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, further worsening 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 when these two conditions co-occur.
Children born with craniofacial anomalies are at increased risk of low self-esteem and bullying. 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 reconstruction of the auricle with alloplastic implantation or costal cartilage autografting.
As surgical techniques have evolved, particularly that of reconstruction with autologous costal cartilage, many surgeons have elected to postpone surgery 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 implants later. Auricular reconstruction is challenging and is associated with several surgical complications; it should ideally be performed by teams with experience and high volume.
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. 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. The first branchial arch, (Mandibular Arch or Meckel's Cartilage) gives rise to Hillocks of His 1-3 and forms, respectively: tragus (1), helical crus (2), and helix(3). The antihelix crus (4), antihelix (5), and lobule and antitragus (6) are formed from the second branchial arch, also known as the hyoid arch or Reichert's cartilage.
Importantly, the stapedial artery also arises from the second branchial arch and if it degenerates too early, it can cause microtia. Ultimately, these six hillocks fuse to form the auricle by 22 gestational weeks of age. The auricle develops to be 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 surgery at earlier ages, particularly if they are not using autologous rib grafting.
While microtia may occur in isolation, it is sometimes associated with genetic syndromes with craniofacial abnormalities such as Goldenhar, Treacher-Collins, Pierre-Robin sequence, Nager, Crouzon, and CHARGE syndrome as well as others. Teratogens such as isotretinoin, thalidomide, alcohol, and mycophenolate mofetil, when used during pregnancy or conception, can also result in microtia. Other risk factors include being a first or high maternal parity, advanced maternal or paternal age, high altitude (above 8,200 feet), and low birth weight.
Microtia is usually unilateral (77% to 93%) more often on the right side (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 Hispanics.
The normal fully developed human ear is approximately 6 cm in height, sloped 20 degrees posteriorly from vertical, with an auriculocephalic angle of 20 to 30 degrees and 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 do a complete head and neck exam to include examining the mandible, oral cavity and palate, eyes, facial nerve function, and taking note of the skin color and quality as well as the level of the hairline and position of the ear 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.
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 a unilateral atretic ear, though 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. 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.
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 5 is associated with the poor candidacy for surgical repair.
Management of the microtia ear varies and escalates from a do-nothing approach to treatment, including prosthetic ear placement or 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 ear is an excellent option and can be affixed to the ear 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 prosthetic. Downsides include prohibitive cost and the risk of a young child losing their prosthesis accidentally. Caucasians or those with light skin may require two prosthetics 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 (Medpor), a newer technique that is becoming more popular, largely due to the difficulty of achieving consistently excellent cosmetic results with autologous cartilage ear reconstruction. In this method, a pedicled temporoparietal fascia (TPF) flap at least 11 cm wide by 12 cm high is harvested through an external scalp incision, endoscopic harvest, or mastoid incision. The flap is used to cover the entire implant with vascular 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 ear. Full-thickness skin grafting from the postauricular surface of the contralateral ear is often required to complete the coverage of the postauricular sulcus.
Advantages to this reconstruction method include reliably natural-appearing contours of the ear, no need for cartilage harvest, saving operative time and patient morbidity, eliminating the risk of pneumothorax, and the concern for calcified cartilage. Potentially, the reconstructive surgery could be offered and 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 authored by Tanzer's pupil, Brent, and later by Satoru Nagata. The concept of the operation is consistent. However: an ear framework is created from rib cartilage, which is shaped with scalpels, osteotomes, and biopsy punches and fixated together with permanent suture or steel wire. The construct is then 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, and contralateral ear, as well as the needed costal cartilage. 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 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 step 1, and then covered by skin and sutured 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 are separated to diminish the risk of necrosis due to decreased blood supply to the ear.
Brent's method differed slightly in that in the first stage, and he would harvest, carve and place the cartilaginous framework in a subcutaneous pocket at the site of the microtic ear; the second stage would then be the transposition of the lobule, reversing the order of Tanzer's first two stages. His 3rd and 4th stages again elevate the construct and creation of a tragus while excavating the conchal bowl.
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 temporoparietal fascia flap and skin graft. Another difference in technique is that Nagata harvests ipsilateral rib cartilage, rather than contralateral, as Brent and Tanzer described. 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. 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.
When considering surgical repair, caution is warranted if the patient has had surgery or trauma to the area, as 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 they have suitable costal cartilage available and are motivated to participate in their 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.
Microtia is sometimes associated with congenital defects; therefore, syndromes such as Goldenhar, Treacher Collins, and others mentioned above should be considered. Other common defects such as prominauris, cryptotia, cup ear deformity, and lobule deformities may be mistaken for microtia. Aural atresia is often associated with grade 3 and 4 microtia and should be evaluated.
Prognosis depends on the outcome measured and which treatment approach was undertaken. A bone-anchored hearing aid can be applied to overcome conductive hearing loss with great reliability and in some cases, the auricle can be concealed with long hair. Similarly, the application of a prosthetic creates an ear that allows the patient to escape social scrutiny and can function to support reading 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.
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 feel about an auricular prosthesis.
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 (pseudomonas), cartilage framework extrusion, changes in framework size, lobule necrosis and migration of the construct from its original location. Compression ischemia with loss of skin and TPF flap is also an early complication of Medpor implantation. Facial nerve injury can occur due to a lack of predictable course in an anatomically maldeveloped ear, particularly with atresia aural repair. Additionally, children can lose their prosthetic ears which are 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 Medpor implants can migrate after placement, usually anteroinferior, although determining the correct location initially 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, Medpor has the potential to extrude or be infected with comparatively minor trauma compared to autologous cartilage constructs in the longterm.
Lastly, most patients will have a low hairline on the microtic side; this can cause result in hair-bearing scalp covering the top of the reconstructed ear, which will later require removal with a laser.
It is critical to educate patients with microtia on the myriad treatment options at the initial visit. 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 syndromic complications associated. Discussion about the timing of interventions is crucial and the need for surgical intervention of comorbid conditions such as aural atresia must be taken into account.
Prenatal counseling regarding the avoidance of teratogens should be performed during maternal prenatal counseling.
Microtia reconstruction is one of the most complex surgeries in plastic surgery. It requires much experience in order to avoid the many potential complications of autologous cartilage reconstruction. Knowledge of the timing of the surgeries as well as collaboration with 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 as well, particularly oncologic resection and avulsive trauma.
The most important consideration to improve outcomes in the treatment of a patient with microtia is early and clear communication between the surgeon and 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 good 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. Good working relationships between the plastic surgeon and the otologist are also essential in order to coordinate staged repair of the microtic ear and any associated aural atresia.
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