CONGENITAL ATRESIA & MICROTIA OF THE EAR
By Mark J. Levenson, MD, FACS, PC
Congenital Atresia, the absence of the external ear canal, is a birth defect which is almost always accompanied by abnormalities of both the middle ear bones in various degrees, as well as the external ear. When it occurs in both the newborn's ears, the pediatrician must readily refer the child to both a facial plastic surgeon and an ear surgeon, as well as an audiologic team.
The degree of hearing loss brought about by the atresia must be evaluated immediately. If both ears are affected, early hearing aid fitting is called for. Using a bone type of hearing aid which bypasses the obstruction, vibration on the bone allows for normal development of speech in the child.
Congenital Microtia, also a birth defect, is an abnormal condition in the growth of the external ear. These are classified by degree. They can vary from minor abnormalities of the helical ear folds to a marked absence of ear development. The presence of a small tag of skin and cartilage may be the only indication of an external ear.
The Congenital Ear
Repair of congenital microtia requires the coordinated efforts of both facial plastic surgeon and ear surgeon. Reconstruction of the microtic ear is usually delayed until the child is four to five years old. At that age, cartilage from the rib is used to reconstruct the external ear. Several operations may be necessary. The ear surgeon will usually delay reconstruction of the external auditory canal, (i.e. correction of the atresia), until the initial phases of the microtia repair are completed.
Microtia does not always occur along with atresia. Isolated atresia can occur in an ear which appears normal. Microtia repair falls under the province of the facial plastic surgeon, so a complete explanation of this surgery will not be offered here. Microtia is a most obvious abnormality. Any child with microtia should be seen early by an ear surgeon in order to coordinate the procedure between the facial plastic surgeon and ear surgeon. In addition, testing for hearing in both ears is indicated early, using Brain Stem Evoked Response Audiometry. This testing must be done early to determine the adequacy of hearing in the "normal" ear, as well as to confirm whether it is really normal.
Congenital artesia can occur without the usual congenital abnormalities of the external ear. Classically, however, atresias occur in conjunction with some deformity or microtia. The degree of microtia or external deformity does not always indicate the degree of abnormalities of the middle ear. A rough estimate of the degree of middle ear abnormalities can usually be made based on the degree of microtia, because both the external ear and the ear canal and bones of hearing occur in pregnancy at about the same time. The ear surgeon should be consulted early, although a commitment for a surgical procedure for correction of the child's atresia usually need not take place until the child is four or five years old.
Parental Reaction and Early Counseling
The birth of a child with an external ear deformity requires early counseling and intervention by the pediatrician who should refer to a team of facial plastic and ear surgeons. They can inform the family of future prospects. The fitting of a bone conducting hearing aid should also be an early decision, particularly in a child with bilateral atresia. If it seems that atresia is unilateral, that it is in one ear only, then the status of normal hearing in the opposite ear must be clearly established.
If normal hearing is determined, then hearing aid amplification is not necessary. These children will develop normal speech patterns without impairment and correction of microtia and atresia becomes an elective choice.
Assessment of the Deformity
Once the child's hearing status has been determined and the ear surgeon consulted, further evaluation is usually deferred until the child is older. In unilateral atresia, the confirmation that the hearing in the opposite ear is normal takes a great deal of pressure off the parents. We know that these children will develop normally. Evaluation for reconstruction can wait until the child is four years old.
In children with bilateral atresia, the anxiety level is significantly higher. Evaluation of the atresia and the development of the middle ear is usually conducted earlier.
CT Scan Findings
When the child is three or four years old, a CT Scan is generally performed. The CT Scan must be of high resolution. It should be performed by a radiologist who is very experienced with scanning the ear and temporal bone. The CT Scan results are extremely important.
In most cases of atresia (or lack of development of the external ear), there is a bony plate which separates the external ear from the contents of the middle ear where the bones of hearing are present. This bony plate varies in thickness. Also, in cases of complete atresia, there is no external ear canal present; there is a complete obstruction of the external opening by skin. Other cases of atresia may demonstrate a small rudimentary external ear canal which is just narrower and much thinner than usual.
Bones of Hearing
The bones of hearing can be properly evaluated as well by an accurate CT Scan. In most cases, the hammer and anvil malleus and incus are somewhat deformed. They may or may not be in contact with the stirrup or stapes bone lying underneath them. The position of the facial nerve is of great importance. The facial nerve follows a course out of the brain and through the temporal bone or bone of the ear. Generally, it courses through the middle ear below the bones of hearing and then exits into the face at the bottom of the mastoid bone which is the pointed tip of bone that is closest to the jaw joint behind the ear.
The facial nerve may be in normal position in cases of atresia. Often, however, it follows an abnormal course. A determination of this course becomes extremely helpful when the ear surgeon is advising parents about surgical reconstruction of the ear. Additional information regarding the formation of the inner ear, cochlea, and labyrinth (i.e. hearing and balance parts of the inner ear) are also obtained from the CT Scan.
The inner ear develops a little earlier in pregnancy. Thus, there may not be an abnormality of the inner ear structures in most cases of atresia. The development of the middle ear space and mastoid bone is also very important in the assessment of reconstructive potential A good estimate of the size and depth of the middle ear cavity can be obtained with the CT Scan.
Surgical Reconstruction: Assessment
The surgical reconstructive potential of congenital atresia is generally made after the CT Scan has been fully evaluated. The parents are advised on the potential for reconstruction, based on the degree of development of the child's middle ear, inner ear, and mastoid, as well as the position of the facial nerve and the relative absence of or deformity of the bones of hearing. The most important factor is the development of a good middle ear cavity, not necessarily the size or shapes of the bones of hearing themselves.
The ear surgeon will see and evaluate the child on a yearly basis until age four. At four, if there is a microtia, plans should have already been made by the facial plastic surgeon for reconstruction of the microtia. Coordination between the ear surgeon and the facial plastic surgeon is essential. Scarring could occur when the ear surgeon performs the initial stages. It could compromise the graft material introduced by the facial plastic surgeon.
Most surgical teams advise that the initial microtia repair be performed prior to the ear surgeon's correction of the atresia. The placement of the position of external ear canal must also be coordinated. Relative risks of the surgery versus benefits must be discussed at length with the family. This must be done prior to surgical intervention. No cases of atresia surgery are routine. Finding the unexpected is routine in these cases. Thus, the ear surgeon must give the family a realistic assessment of the potential for reconstructive success, as well as hearing in the involved ear or ears.
Once the ear has been opened, the surgeon must determine where to create the bony opening which will reach the bones of hearing. The external surface of the ear is evaluated and the bony opening must not be made excessively large or enter into the mastoid bone.
The key is to create an adequate opening that will come down directly over the bones of hearing. The plug of solid bone is drilled away by utilizing an air drill.
This is done meticulously, to prevent drilling on the bones of hearing which are often attached to the undersurface of the bony plate. Once the bones of hearing are identified, they must be released from attachments to the bony wall around them. Ear surgeons use the high power operating microscope and diamond dust burrs which gently free the bones of hearing from the bone of the ear canal Once the bones have been fully freed and the middle ear space exposed, the raw surfaces of the bony ear canal must be relined with a skin graft or the ear will close down in a scar.
The Surgery: Skin Graft
A very thin skin graft is generally harvested from the thigh or lower abdomen. This graft is ten 1,000's of an inch in thickness. A facial graft, tissue from behind the ear drum, is also thinned and utilized to create a new eardrum. The facial graft is placed directly on the bones of hearing. The skin graft is placed tightly against the raw bone of the external auditory canal As much skin as possible is preserved from the outer ear and folded into the canal.
Reconstruction of the middle ear may be essential as there is no connection between the hammer and anvil (malleus and incus) and the underlying stapes bone. In addition, these bones may have different degrees of abnormal development, requiring removal and eventual replacement. All attempts are made to reconstruct at the primary procedure if possible.
The position of the facial nerve is continuously monitored with a facial nerve monitor. It is vital to identify the postion of the nerve. This is routinely performed in order to avoid damage to it. The external ear canal is then generally packed with firm balls of gelatin sponge and silicone sheeting. When the operation is completed, the external ear canal should be completely covered by skin graft.
Raw, exposed bony areas could result in infection and local scarring which could lead to the loss of the newly created canal All packing is removed two weeks after surgery in an office procedure.
If selection for reconstructive surgery is made carefully, hearing results can be excellent. It is important not to intervene surgically in cases where reconstructive possibilites are nil -- complete lack of development of the middle ear space and/or marked deformity of the inner ear. Successful reconstruction may not bring totally perfect hearing to the involved ear, but success is measured by bringing the hearing back into the normal range.
Alternatives to surgery include no intervention in a unilateral or one sided atresia, or use of a bone-implantable hearing aid into the mastoid bone behind the external ear. These alternatives must be carefully discussed with the family. In the case of an adult with atresia, the options should be aired prior to surgical intervention.
The normal ear canals clean themselves by the migration of skin from the external ear canal. This process does not occur in individuals with atresia reconstruction. Skin may accumulate in the external ear canal and must be removed in most patients who have undergone atresia repair at least once a year. In addition, because there is lack of normal wax or cerumen in the ear canal, the skin grafted bony ear canal is more susceptible to ear infections when it comes in contact with water. The use of ear plugs will always be necessary for swimming.
Over the past 40 years, correction of microtia and atresia of the ear has become an increasingly successful reality for children born with this birth defect. Cases should be chosen appropriately and selectively. CT Scanning is extremely important in the accurate assessment of the development of the middle ear space. If the middle ear space is totally or almost completely absent, then surgery is usually not advisable. Alternative procedures such as implantable bone conduction hearing aids have been found to be an excellent option as well.
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