Treatment of microtia:past，present and future

·综 述·

Treatment of microtia:past，present and future

The purpose of this review article is to review the reconstructive method available for the treatment of microtia and highlight the recent advances. The well established technique developed by Brent and Nagata are still must widely performed procedure for microtia reconstruction. Various modification of this technique has been reported in the literature. Synthetic framework is seen as an alternative to autogenous costal cartilage framework because of ease of the procedure. More recently， tissue engineering is seen as the most promising treatment. This article gives an overview of the current practice in the field of microtia reconstruction and summarizes the recent surgical developments and relevant tissue engineering research.

Microtia; anotia; autogenous cartilage; synthetic framework; tissue engineering

1 Introduction

Microtia is a congenital malformation of the external ear that ranges in severity from mild structural abnormalities to the complete absence of the ear (anotia). Microtia can occur as an isolated birth defect or as part of a spectrum of anomalies or a syndrome. It can occur unilaterally or bilaterally; in unilateral cases right side is more affected[1-2]. The prevalence rate of microtia ranges from 0.83 to 17.4 per 10 000[2]. As ear is the prominent part of the head， microtia is associated with the psychological health concern to both patient and family.

The techniques for auricular reconstruction using autogenous rib cartilage employed by the majority of surgeons have been well established for a number of years. These will be reviewed， as will some contemporary modifications to these techniques. More recently， synthetic implants have been employed for auricular reconstruction in a smaller number of centres and recently published results using this technique will be reviewed.

The recent advancement in the development of tissue engineering holds the great promise for the microtia patient. Lab prepared auricular framework might be the standard treatment for microtia patient in future.

2 Timing of surgery

There is no universal consensus on the timing of microtia surgery. One factor which urges the family member for early surgery is the psychological problem the child might encounter with increasing age. Another consideration is the normal growth rate of the auricle. At birth， the auricle is 66% of its adult size; by age 3， it is 85% of its adult size; by age 6， it is 95% of its adult size[3]. Thus， most surgeon prefer to perform microtia surgery after age 6. Finally， reconstruction can often begin at an earlier age if synthetic framework is being used， because there is no need to harvest rib cartilage.

3 Auricular reconstruction using autogenous costal cartilage

Gillies is credited with the first use of rib cartilage for construction of an auricular framework in 1920. The modern era of auricular reconstruction began with Tanzer who reintroduced the technique of autogenous costal cartilage grafts as a method of auricular reconstruction[4]. A significant majority of surgeons worldwide continue to use techniques using autogenous rib cartilage to reconstruct the auricular framework. According to the latest national survey of American Society of Plastic Surgeons， 91.3% of the plastic surgeons choose autologous cartilage staged reconstruction for patients with microtia[5]. The technique described by Brent[6]， Nagata[7]and Fermin[8]are most widely used technique. Various modifications have also been employed on these techniques. Although most surgeons would agree that a successful autogenous ear reconstruction is ideal， critics would argue that currently the aesthetic results are very inconsistent and often poor.

4 Complications associated with autogenous costal cartilage technique

A systemic review by Long et al.[9]reported 1 525 cases of complication out of 9 415 patients， overall complication incidence being 16.2% in average with a range of 0-72.9%. The most common complication of the recipient site include infection and hematoma. Other complication include graft skin necrosis， frame exposure， cartilage absorption， hypertrophic scar， facial never injury， asymmetry. The demerit of this technique is that donor site might also be left with complications like atelectasis， pleural tear， chest wall deformity， thoracic scoliosis， hypertrophic scar.

5 Auricular reconstruction using synthetic implants

This technique involve the use of ready-to-use auricular framework composed of synthetic material called porous high-density polyethylene (Medpor)[10]. It is stable， inert substance， which has ability to integrate with human tissue due to its increased porosity. The key advantages of this technique is that, the surgeon don′t need artistic and technical skill to sculptor realistic looking ear and avoiding the donor side morbidity. This technique is generally performed in two stages. In first stage， temporoparietal fascial flap (TPF) is required to cover the synthetic implant and a full-thickness skin graft is harvested and used to cover TPF over the implant. The second stage of the procedure involves lobular transposition after an interval of around 3 months.

6 Complications associated with synthetic implants

The most common complications associated with synthetic implants are infection and implant exposure. Romo et al.[10]in their study reported a complication rate of 4% over 250 cases. Similarly， another study of Medpor craniofacial implants by Cenzi et al.[11]reported 6.3% complication rate.

7 Recent modifications in surgical technique

Although the surgical technique developed by Brent and Nagata are most widely performed surgical procedure for microtia reconstruction but surgeons around the world have made various modification to their technique. The technique to reconstruct ear using tissue expander was first described by Tanino et al.[12]. This innovative technique was further revised by Pan et al.[13]since 1994 . They made the use of tissue expander in the mastoid process which is expanded of period of time and use this space as a pocket for cartilage framework. The major advantage of this technique is the avoidance of skin graft to cover the framework. This technique is performed in three stages. First stage involves the implantation of tissue expander， second stage is the ear reconstruction using autogenous cartilage framework and third stage is the construction of pseudomeatus and formation of tragus. Their study reported most of the patient with microtia were satisfied after ear reconstruction during 3-5 years follow-up period. This technique is now widely performed in my institution in China.

Another modification to the 2-stage Nagata technique have been described by Jiang et al.[14]. The advantage of this technique is that there is no need for skin graft. In this 2 stage technique， first stage involves the fabrication of 3-dimensional cartilage framework. The skin flap and retroauricular fascial flap are elevated in the mastoid area. Then the framework is wrapped by the fascial flap from behind and covered by the skin flap from front. In the second stage the crus， the tragus， and the conchal cavity are reconstructed. The author reports a consecutive series of 68 cases， all of which retained the three dimensional configuration of the cartilage framework.

8 Future of microtia surgery

To date， no material， autogenous or prosthetic， is available that perfectly mimics the shapely elastic cartilage found in the ear. With the rapid development of tissue engineering many surgeons believe tissue engineering holds the future for microtia surgery. Based on the national survey conducted by Im et al.[5]in America 59% of all surgeons believe that in 15 years tissue engineering will represent the gold standard of microtia reconstruction(as per 2013 report). Excellent reviews of the current state of tissue engineering in auricular cartilage reconstruction were published in 2012 by Bichara et al.[15]and Nayyer et al.[16]. To produce a tissue-engineered auricle， the first challenge is to create a three-dimensional scaffold on which the chondrocytes are grown. The scaffold is made from either a polymer or an organic material. Further steps involve obtaining a suitable cell source and biological factors to sustain the phenotype and tissue function. Ready composite is grown in vitro or implanted.

Lee et al.[17]reported a innovate technique which made the use of MEDPOR framework and autogenous chondrocytes. This study investigated whether cartilage tissue， engineered with chondrocytes and a fibrin hydrogel， would provide adequate coverage of a commercially used medical implant. This study concluded that the framework became encased in neocartilage following implantation.

The credit for new method of microtia reconstruction goes to Yanaga et al.[18]who make the use of cultured autologous auricular chondrocytes to generate the ear. In this technique， they harvested auricular cartilage chondrocytes， expanded their numberinvitroand allowed the chondrocytes in culture to produce an extracellular matrix of immature cartilage. This was used as the scaffold and fibroblast growth factor was added. This matrix was then implanted by injection into a subcutaneous pocket on the fascia of the lower anterior abdominal wall.

The implant was then allowed to mature for 6 months before being removed， producing a construct of mature cartilage. This cartilage was harvested surgically， sculptured into an ear framework， and implanted subcutaneously into the position of the new ear. No absorption of chondrocytes was observed in 2 to 5 years follow-up period.

9 Challenges with tissue engineering

Long-term sustainability and plasticity remain some of the challenges in auricular tissue engineering that need to be addressed. Appropriate scaffold design is essential because the ear must be designed specifically for the patient. Another problem arises with the use of stem cells as a cell source. This may lead to uncontrolled proliferation of the cultured material with the possibility of tumor formation. Therefore， further investigation of mechanisms by which cells may be controlled is paramount. Concerns also arise with the possibility of infection and increased morbidity observed with the use of artificial prostheses.

10 Conclusion

The surgical technique developed by Brent and Nagata are still most widely performed procedure for the reconstruction of microtia. Various modifications made to these traditional techniques are also widely performed. Recently synthetic implants have shown promising results with the advantage of avoiding donor site morbidity. With the rapid development of tissue engineering， it would not be wrong to say that tissue engineering holds the future of microtia surgery.

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TRIPATHEE Sanjib1，2，XIONG Meng2

(1.SchoolofMedicine，SouthEastUniversity，Nanjing210009，China；2.DepartmentofPlasticandReconstructiveSurgery,ZhongdaHospital,SoutheastUniversity，Nanjing210009，China)

XIONG Meng E-mail:bearbrave@sina.com

format] TRIPATHEE Sanjib，XIONG Meng.Treatment of microtia:past，present and future[J].J Southeast Univ(Med Sci Edi)，2015，34(3)：485-488.

R62 [Document code] A [Article ID] 1671-6264(2015)03-0485-04

10.3969/j.issn.1671-6264.2015.03.040

[Received date] 2014-12-20 [Revised date] 2015-01-14

[Biographies] TRIPATHEE Sanjib (1984-)，M，Nepalese，Nepal,Postgraduate student.E-mail:sanjibatny@gmail.com