Lecture Topic: APPLICATION OF ALLOGRAFT IN OTOLARYNGOLOGY
Congenital Malformation of the Ear.
Embryology: The primordia of the external ear are the tissues of the first and second brachial arches.
The middle ear is formed from the end of the first pharyngeal pouch and the surrounding mesenchyme which also is part of the first and second branchial arches. Because a failure in the development of one part influences the neighboring areas and all subsequent development, it is not surprising that congenital defects of the external and middle ear usually occur in combination and many times with congenital defects of other system. The labyrinth develops from an entirely different primordial tissue, which is rarely influenced by maldevelopment of the middle ear (except the oval window region) and therefore cochlear function is normal in most of these cases.
The most commonly occurring defects are protrusion of the auricle also called lop or outstanding ear and macrotia, microtia, stenosis or atresia of the cartilaginous and or bony external auditory canal, ossicular malformation, restricted or absent development of middle ear or mastoid spaces and preauricular fistula.
Causative factors influencing anomalous development of the ear are unknown, It has been established that drug intoxication occurring between 28th and 42nd day after fertilization may result in anomalies (4wh – 6wh) drug thalidomide used in western Europe between 1958-1962.
Unilateral involvement is reported more often than bilateral, men are affected more than women in ratio 2 : 1 to 5 : 1.
Exact incidence of congenital defects of the ear is unknown but obvious defects occur in at least 1 of 10 000 births and perhaps double this number.
Classification of Defects by Henna
Class I: In this category are those with the least abnormality. The external ear is shaped normally and of near normal size. The external auditory canal may be smaller than normal, but the tympanic membrane is mobile.
Class II: The defects in this class are more severe than in the first group. Class II anomalous microtia of varying degrees is associated with stenosis or usually, atresia of the external auditory canal. The ossicles are deformed, the mastoid is pneumatized and the middle ear is of fairly normal size.
Class III: The most severe degree of malformation. The malformation listed in Class I are combine with a marked limitation in the middle ear space and mastoid cell development.
The Metz classification of auricular malformation.
Several authors have used the classification of Metz to describe the degree of deformity of the auricle.
Grade I: Deformity indicates a definitely misshapen auricle but one of which most of the Landmarks, such as tragus, helix or lobule may be recognized.
Grade II: Deformity consists of a hookshaped or question mark appearance in the top curve represents the rudimentary helix. This is the most common deformity.
Grade III: Deformity is more severe than grade II with only one or two misshapen protuberances marking the position of the lobule.
The most useful information gained from these views is the extent of pneumatization of the attic and mastoid and the position of the middle fossa dura in relation to the planned surgical approach to the attic.
The patient with congenital ear disease presents a problem whose management demands individual solution. These defects not only affects the communicative ability but also introduce a severe psychologic handicap because of the disfigurement. Even a unilateral hearing loss may become a handicap. The seemingly minor problem of wearing eyeglasses can be difficult to solve these patients.
The most urgent problem is that of hearing loss in bilateral involvement. Speech begins to develop during the first year of life, but hearing is necessary for this learning to occur.
Adequate screening methods are now available to obtain a close approximation of the hearing threshold in infants by free field measurement.
Early hearing aid fitting masks possible the accurate assessment of cochlear function. No surgical procedure should be done until a complete evaluation has eliminated. The most urgent problem is that of hearing loss in bilateral involvement.
The best resolution of cosmetic problem has not yet been decided. There are many who feel that plastic reconstruction of the auricle is the solution that gives the most benefits to the patients.
Only a few plastic surgeons are skilled in the difficult process of multiple operation. In this situation, the recommendation of a prosthesis is probably the best solution. This problem is less critical in girls, who may adopt hair styles which hide the deformity. When a skilled plastic surgeon is available, reconstruction has much advantage to the patient. Ideally, the plastic surgeon and the otologic surgeon work closely together in the planning and management of these cases.
Techniques of Surgery:
Incision: minor narrowing of the canal may be corrected by widening with burs after elevation of the overlying skin.
Reconstruction of the canal:
Many surgeon choose modified radical mastoidectomy in every case of congenital atresia of the external auditory canal, but the risk to facial nerve is greatest with this approach.
The methods used in hearing restoration are extremely variable and depend on the deformity present.
One of the more difficult problems in the surgery of canal atresia is maintaining the lumen of the canal externally.
Plastic Reconstruction of the Auricle:
The basic technique of auricular reconstruction used today involves the burying of a framework in the normal position of the auricle.
The skin over this framework becomes the outer intequement of the auricle and the skin of the medial surface is grafted.
The auricular framework may be formed from autogenous cartilage removed from the coastal margin.
The artificial material are not tolerated as well as the autogenous cartilage graft.
After a healing period of several months, the skin and underlying framework are elevated and the raw surfaces of the auricle and underlying tissue over the mastoid are covered with a skin graft held with a stent.
Modern plastic are available that imitate skin texture closely, and nonirritating glues provide from attachment of the prosthesis. When there is a choice between surgical reconstruction or prosthetic replacement available to the patient, the patient and his parents should be given the opportunity to make the choice after being acquainted with the factors involved.
A cartilage graft is modeled and inserted into a subcutaneous pocket behind the deformed auricle.
The cartilage graft is held with stay sutures.
At the second stage, the implanted cartilage is dissected up from behind and a skin graft is placed to form the posterior surface of the auricle.
At the third stage, portions of the deformed auricle are used to fashion the lobule and root of the helix.
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