The risk of microtia increases with maternal parity beyond four pregnancies, especially with anotia (the most severe form). Males are twice as likely to have microtia compared with females of the same race. Microtia displays significant racial variance with increased incidence in people of Japanese and Hispanic descent compared with whites. Some nonpopulation studies have shown exceptionally high risk in Navajo Native American, Chileans, and Ecuadorians. Unilateral microtia is far more common than bilateral, representing between 75 and 93% of cases. Right-sided microtia is most common (60%). The overall incidence varies from 8 to 43:100,000 births. Other risk factors include advanced maternal age, maternal insulin dependent diabetes mellitus (IDDM), advanced paternal age, multiple births, low birth weight, acute maternal illness, and teratogens such as alcohol and Accutane.1–4
The traditional theory of ear development suggests that the ear develops from the first and second branchial (pharyngeal) arches (not the second and third). It arises from six buds of mesenchyme, known as the hillocks of His. These were originally described by Wilheim His, hence the name. These are numbered from 1 to 6 with the first three formed by the first arch and the second three formed by the second arch. Each hillock relates to an adult component of the ear: Hillock 1: Tragus Hillock 2: Helical root Hillock 3: Ascending helical rim Hillock 4: Superior scapha and helical rim Hillock 5: Inferior scapha and conchal bowl Hillock 6: Lobule The external auditory canal is formed by the first branchial (pharyngeal) cleft. The first 6–8 weeks of gestation (i.e., the first trimester) are the most significant with regard to development of microtia so teratogens would have impact at this stage of development.1–3 There have been newer concepts described regarding human auricular development. One suggestion is that the contribution of the posterior hillocks is limited to the concha, the body of antihelix, the triangular fossa, and the inferior crus. In this model, the helix, scapha, and superior crus are derived from the “free ear fold’ that develops separately from the second pharyngeal arch hillocks from tissue immediately caudal to the second arch. This theory therefore does not suggest hillocks do not exist (Fig. 32.1).4
2012;158A(1):124–139 3. Castilla EE, Orioli IM. Prevalence rates of microtia in South America. Int J Epidemiol 1986;15(3):364–368
4. Jaffe BF. The incidence of ear diseases in the Navajo Indians. Laryngoscope 1969;79(12): 2126–2134
Conductive hearing loss affects around 90% of patients with microtia and therefore bone-anchored conductive hearing devices have a key role in management of these patients. This is important to consider in the multidisciplinary setting as the type of surgery and the order of surgery both need to be discussed by the otologist and plastic surgeon. For example, middle ear surgery is usually performed after autologous auricular reconstruction whereas if alloplastic reconstruction is planned, the canal is reconstructed first. Either way, it is important to liaise with the otologist to plan access so that flap and skin vascularity are not compromised, and optimal aesthetic positioning can be achieved.1 Silastic frameworks as described by Cronin2 have high extrusion rates, so they are not currently used in spite of the early excellent aesthetic appearance. In contrast, porous polyethylene implants for ear reconstruction were also shown to have good short-term aesthetic results and low rates of extrusion, and now, longer term results have proven to be good. 3,4 Osseointegrated prosthetic reconstruction has a role in many cases and should not be reserved solely for cases in which autologous reconstruction has failed. Although outcomes will be affected by the availability of skilled anaplastologists and manufacturing procedures, prostheses can provide very good aesthetic outcomes. They are particularly useful following trauma, cancer, irradiation, and in the elderly.5
The Marx/Rogers classification system is popular because it is simple and straightforward to use. It has just four classification grades and considers the appearance in simple descriptive terms only. It does not accurately guide surgical management, nor consider the finer anatomic details of the ear.1,2 The Weerda3 and Tanzer 4,5 classifications provide far greater detail and the Nagata6 classification is said to help guide surgical management. None of the classifications consider the hearing disability. Both the Tanzer and Weerda classifications consider prominent ear, but the Marx classification does not do so (Table 32.1). Table 32.1 Classification Systems for Microtia Grade I features of an ear A smaller than normal auricle with all others normal Grade II structures An abnormal auricle with some recognizable normal Grade III structures An abnormal auricle with some nonrecognizable normal Grade IV Anotia
correct? The Nagata1 technique for ear reconstruction is a two-stage procedure (not three) that uses ipsilateral costal cartilage from ribs five through nine. It cannot usually be performed until 10 years of age because cartilage volume is insufficient before this time. In contrast, reconstruction with porous polyethylene can be undertaken at age 5. The first stage of the Nagata technique involves creation of a cartilage construct from ipsilateral ribs six to nine. Most but not all of the perichondrium is left in the chest wall to minimize residual deformity. The construct is placed in a subcutaneous pocket, and simultaneous lobule transposition is performed. Tragal reconstruction is also performed during this stage. The second stage is usually performed 6 months later, and further cartilage is harvested from the fifth rib (unless it has already been banked) to provide a wedge underneath the main cartilage construct. A temporoparietal fascial flap is elevated and inset to cover the grafts. This is then covered with split-skin graft from the scalp.1–5
The key to successful outcome with high-density porous polyethylene ear reconstruction is to achieve total implant cover with a robust temporoparietal fascial flap. Reinisch found that extrusion rates were reduced from 44 to 7.3% by obtaining this complete coverage. During this procedure, a two-piece prosthesis is used. However, Reinisch prefers to avoid suturing the construct together and instead solders it with high temperature ophthalmic cautery. Following surgery suction drains are used under the implant and at the flap donor site, but these are removed the following day. Skin is provided by the microtic ear as well as from the mastoid and the contralateral posterior ear skin. These are used to graft the anterior aspect of the new ear over the temporoparietal flap. Further full-thickness graft is harvested from the groin and used to resurface the posterior aspect of the construct. A splint is used following surgery, but it is made from silicone, not foam. Furthermore, it is not premade, but is instead made on table using dental impression material. This is sutured to the scalp and left for 2 weeks and exchanged for a night splint that is worn for 6 months.1–3
The most common late complication in ear reconstruction is chest wall deformity, which occurs in approximately two-thirds of cases. It is affected by age at the time of surgery and is reduced when surgery is performed after the age of 10. It is also reduced by leaving perichondrium at the donor site.1,2 The most significant early complications are skin loss, infection, and hematoma, all of which are rare. However, each must be identified early and managed accordingly to prevent extrusion of the cartilage framework. Areas of skin loss should be debrided and only reconstructed if the area is greater than 1 cm. Smaller defects can be managed with dressings. Avoiding pressure dressings and replacing them with small suction drains has been shown to reduce skin-related complications from 33 to 1% in Brent’s series.1 Hematomas are not self-limiting and must be drained immediately to minimize risk of skin loss. Reconstructed ears commonly remained the same size over time (48%) but many increased in size as the child developed (42%) in Brent’s series.1