Any disease process which interferes with the conduction of sound to reach cochlea causes conductive hearing loss. The lesion may lie in the external ear and tympanic membrane, middle ear or ossicles up to stapediovestibular joint.
The characteristics of conductive hearing loss are:
□ Negative Rinne test, i.e. BOAC.
□ Weber lateralised to poorer ear.
□ Normal absolute bone conduction.
□ Low frequencies affected more.
□ Audiometry shows bone conduction better than air conduction with air-bone gap. Greater the air-bone gap, more is the conductive loss.
□ U Loss is not more than 60 db.
□ Speech discrimination is good.
MANAGEMENT
Most cases of conductive hearing loss can be managed by medical or surgical means. Treatment of these conditions is discussed in respective sections. Briefly, it consists of:
□ Removal of canal obstructions, e.g. impacted wax, foreign body, osteoma or exostosis, keratotic mass, benign or malignant tumours, meatal atresia.
□ Removal of fluid. Myringotomy with or without grommet insertion.
□ Removal of mass from middle ear. Tympanotomy and removal of small middle ear tumours or cholesteatoma behind intact drum.
□ Stapedectomy, as in otosclerotic fixation of stapes footplate.
□ Tympanoplasty. Repair of perforation, ossicular chain or both.
□ Hearing aid. In cases, where surgery is not possible, refused or has failed.
CONGENITAL CAUSES OF CONDUCTIVE HEARING LOSS
□ Meatal atresia
□ Fixation of stapes footplate
□ Fixation of malleus head
□ Ossicular discontinuity
□ Congenital cholesteatoma
□ Tympanoplasty
It is an operation to (i) eradicate disease in the middle ear and (ii) to reconstruct hearing mechanism. It may be combined with mastoidectomy if disease process so demands. Type of middle ear reconstruction depends on the damage present in the ear. The procedure may be limited only to repair of tympanic membrane (myringoplasty), or to reconstruction of ossicular chain (ossiculoplasty), or both (tympanoplasty). Reconstructive surgery of the ear has been greatly facilitated by development of operating microscope, microsurgical instruments and biocompatible implant materials.
ACQUIRED CAUSES OF CONDUCTIVE HEARING LOSS
External ear: Any obstruction in the ear canal, e.g. wax, foreign body, furuncle, acute inflammatory swelling, benign or malignant tumour or atresia of canal.
Middle ear: Perforation of tympanic mem-brane, traumatic or infective. Fluid in the middle ear, e.g. acute otitis media, serious otitis media or haemotympanum. Mass in middle ear, e.g. benign or malignant tumour. Disruption of ossicles, e.g. trauma to ossicular chain, chronic suppurative otitis media, cholesteatoma. Fixation of ossicles, e.g. otosclerosis, tympanosclerosis, adhesive otitis media. Eustachian tube blockage, e.g. retracted tympanic membrane, serous otitis media.
MYRINGOPLASTY
It is repair of tympanic membrane. Graft materials of choice are temporalis fascia or the perichondrium taken from the patient.
OSSICULAR RECONSTRUCTION
It is required when there is destruction or fixation of ossicular chain. Most common defect is necrosis of the long process of incus, the malleus and the stapes being normal.