Microtia and atresia of the ear canal
Microtia and atresia of the ear canal are anomalies in the development of the osseocartilaginous skeleton of the outer ear. According to statistics, among 10 thousand children in the world one is born with congenital defects of this area. These changes relate to a so-called dizembriogenesis — damages of the anlage and organs formation in utero. Thereafter, the main factors affecting the occurrence of microtia and atresia are the effects damaging the embryo — toxic, infectious, less often — mechanical, as a rule — in the early stages of pregnancy. The most severe changes occur when the embryo is affected by a pathological factor earlier than 7 weeks, after the third month the pathology of the middle ear and the ear canal (atresia) occurs less frequently. The formation of the auricle finishes by the 7th month of intrauterine growth, after this period microtia cannot occur.
Microtia and atresia.
What is it? Microtia is when the external ear is underdeveloped or absent. Atresia of the ear canal is a pathology of the development of the ear canal, its complete or partial absence. Often these conditions are combined with hearing impairment, at least with conductive hearing loss due to the absence of the eardrum, and often the structures of the middle ear. Less common combinations are with the sensory neural hearing loss — a disorder of the auditory nerve itself. Since the development of the ear is consistent, atresia is usually combined with anomalies of the ear canal (about 75% of cases). However, disorders in the structure of the ear canal can also occur in normal ones. Microtia and atresia are unilateral or bilateral.
What to do?
Surgical treatment for correction of ear auricle impaired developments should be divided into two problems — the problem of hearing and the problem of the external appearance.
The amount of actions required depends on the degree of hearing impairment. Actually, the functional assessment of the ear performance can be done by audiologists, even at a rather early stage. The diagnostic technique of the brainstem auditory evoked response allows to identify whether the auditory nerve is alive and whether it is possible to make the child hear.
The second stage is morphology assessment. Multispiral x-ray computed tomography allows to construct an accurate, with a resolution of a fraction of a millimeter, a three-dimensional picture of bone, cartilage and soft tissue structures of the temporal bone region. On the tomogram it will be clear what part of the ear structures is not formed, the condition of the middle ear structures such as the auditory ossicles and the eardrum, which fills the area where the ear canal should be — bone or soft tissue formations. Firstly, these data make it possible to understand how promising the attempt to form the auditory canal in terms of function is. Secondly, these data allow to determine markers that let the surgeon reach the tympanic cavity accurately- the place where the preparation for the sound transmission to the auditory nerve should end. In fact, these two studies determine how much work it makes sense to do from an objective perspective. Based on the same data, it is possible to understand how many steps need to be done and what result can be achieved.
So, what effect is possible? Ideally, we aim to make the child a real, proper ear that looks like an ear, hears like an ear and behaves like an ear throughout a child’s life. The way to achieve this goal lasts for several years, several stages of reconstructive surgery are performed, as a result of which we have to restore the ear canal, eardrum and ear appearance.
The latter, in fact, is almost the smallest problem from the entire list. Just the external ear is the most visible component of the whole complex.
We shall consider the most advanced version. The child has a formed tympanic cavity, there are auditory ossicles and a living auditory nerve, but the ear canal is completely closed and the external ear is missing or incorrectly formed. This is the classic combination of the external auditory canal atresia and microtia.
First and foremost, the child needs the hearing to be raised. It is performed using prosthetics at early stage with special bone-anchored hearing aids. They are special devices that transmit sound to the auditory nerve bypassing the ear, causing the skull bone to resonate, usually through a special metal pin — an anchor that is implanted into the bone. Regardless of your wish to restore the child’s normal anatomy, the hearing aid must be placed as early as possible, it will be the key to the child’s adaptation in society and will greatly facilitate rehabilitation in the postoperative period. From birth to three or four years audiologists and deaf-and-dump teachers must be engaged with a child. With time the structures of the temporal bone and ear come to the state in which they have to stay for their whole life. This period lasts for three — four years old. As soon as the formation of the area is completed — we can estimate it by a computer tomography. Next we can proceed to the surgical stage. The first performed surgery is the formation of the bone canal. A complex and precise surgery that carries most number of risks of complications, is performed by taking into account the knowledge of microanatomy of the area, which is obtained by tomography, often using special navigation tools that “tie” the position of the doctor’s instrument to the reconstructed three-dimensional image on the monitor. This is the most high-tech stage of the surgery. Just because at this stage there are serious risks, we must approach the justification of this stage with all possible responsibility. This stage is not recommended in case of absence of auditory ossicles and in case of absence of the auditory nerve full performance.
However, we face hard choices. The optimal period for the bone canal formation is about 4 years, and we start reconstructing the external ear only at the age of 7−8 years. Therefore, after drilling a canal in the bone, we do not open it outwards, but we fill it with a silicone cylinder. One end of this cylinder stays on the remaining part of the bones, and the other end is under the skin. It performs two tasks. Firstly, even at this stage, hearing without device is noticeably improved. Secondly, this cylinder is a kind of protector that does not allow the osseous tissue to close the defect. The area between the cylinder and the surface of the drilled bone is filled with granulations — loops of small vessels. Afterwards, these granulations become “a bed” for the transplanted skin, which will line the ear canal and provide a quick and accurate engraftment of the displaced skin fragment. The next step is the formation and engraftment of the external ear. This stage is performed at the age of 6−7 years. The ear frame (carcase) can be a child’s own cartilage, taken from the costal arch, or a ready-to-use porous polyethylene known as a Medpor material. Each variant has its pluses and minuses.
Medpor material is delivered ready-made, molded, sterilized and ready for transplantation. Therefore, all we need is to prepare “the bed” for the prosthetic frame and transplant it under the skin. It sounds simple and is performed in a simple way. Where are the minuses? Firstly, silicone frame is a finished factory-made product, that is why the number of ear designs is limited. As a rule, an ear created by this way will differ externally from the second ear with a one-sided microtia. Thousands and thousands of children who have Medpor have exactly the same ears. In addition, we do not have long-term results of such surgeries. There can be difficulties with a long-term effect. As time goes, this ear can change, lose its shape, dislocate like any silicone prosthesis. Unfortunately, the method has been used recently, and there is no complete characteristics of long-term results. In addition, the absence of a live “bed” can lead to eating disorders, innervation and skin sensation disorders over the deformity. The variant with cartilage is more time-consuming and a little more traumatic but it has its advantages. This method consists of making a cut to collect a costal arch fragment. In contrast to the factory-made artificial product, the ear made from cartilage changes with time in shape, it matures. The skin on the ear, which is adapted from the flap on the head, corresponds to the appearance of the surrounding skin, the innervation is preserved and the cartilage tissue serves as a conductor of vascular growth. The ear is red when the patient is ashamed and it turns pale when it freezes. The ear feels the touching. The ear behaves like an ear — this is one of the points that we want to perform during the correction, and this is one of the main differences between the cartilage skeleton method and the Medpor method. The second advantage is that in case of unilateral malformation of the auricle, the formed ear can be made exactly the same as the existing one. Therefore, in spite of the great complexity, the long duration of the process, we consider forming the cartilage skeleton as more preferable. Although in some cases we use Medpor, if medically required. Since this method is less demanding, it can be performed when we expect great technical difficulties, in case of tissue deficiency, inelastic skin in the area. And of course, when it comes to cosmetics surgery, we use this technique in cases where the patient himself wants it.
The final stage of ear reconstruction is the “opening” of the ear canal. This stage requires appropriate tissues state, elasticity and skin supply. It is performed when the outer frame is fully formed, the surrounding tissue has replanted and the ear has acquired its natural appearance. In some cases, the opening of the ear canal is not recommended, for example, when the deformation of the area has led to a significant displacement of the middle ear from the normal position. In such case the opening of the ear canal means a significant disorder in the aesthetic of the final result. Even if you do not perform the opening of the previously formed ear canal, silicone “sound guide”, which is installed at the first stage, allows to achieve a noticeable increase in hearing, usually more than 60%. Moreover, there is no sense to open the ear canal if the middle ear is not formed or does not hear due to a defect in the auditory nerve. These situations require a small incisure — a fold in the tissues, which carries only an aesthetic demand.
Thus, the complex of surgical measures allows to create not only aesthetics, appearance, but also in a large number of cases to give the child a fully functioning organ of hearing. Ultimately, this is our main goal every time we start working with each child.