Blocking of the eustachian tube leads to decreased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles and the tympanic membrane. Acute or Serous otitis media
Chronic suppurative otitis media (CSOM)
Perforated eardrum
Tympanosclerosis or scarring of the eardrum
Cholesteatoma
Eustachian Tube Dysfunction, inflammation or mass within the nasal cavity, middle ear, or eustachian tube itself
Otosclerosis, abnormal growth of bone in or near the middle ear
Middle ear tumour
Ossicular discontinuity as a consequence of infection or temporal bone trauma
Congenital malformation of the ossicles. This can be an isolated phenomenon or can occur as part of a syndrome where development of the 1st and 2nd branchial arches is seen such as in Goldenhar syndrome, Treacher Collins syndrome, branchio-oto-renal syndrome etc. Barotrauma unequal air pressures in the external and middle ear. This can temporarily occur, for example, by the environmental pressure changes as when shifting altitude, or inside a train going into a tunnel. It is managed by any of various methods of ear clearing manoeuvres to equalize the pressures, like swallowing, yawning, or the Valsalva manoeuvre. More severe barotrauma can lead to middle ear fluid or even permanent sensorineural hearing loss. Inner ear
Third window effect caused by:

Superior canal dehiscence – which may require surgical correction. Enlarged vestibular aqueduct
Labyrinthine fistula

Presentation
Conductive hearing loss makes all sounds seem faint or muffled. The hearing loss is usually worse in lower frequencies. Congenital conductive hearing loss is identified through newborn hearing screening or may be identified because the baby has microtia or other facial abnormalities.
On an audiogram, the "x" represents responses in the left ear at each frequency, while the "o" represents responses in right ear at each frequency. CT scan
Most causes of conductive hearing loss can be identified by examination but if it is important to image the bones of the middle ear or inner ear then a CT scan is required. CT scan is useful in cases of congenital conductive hearing loss, chronic suppurative otitis media or cholesteatoma, ossicular damage or discontinuity, otosclerosis and third window dehiscence. Specific MRI scans can be used to identify cholesteatoma. Pathophysiology
Management
Management falls into three modalities: surgical treatment, pharmaceutical treatment, and supportive, depending on the nature and location of the specific cause. In cases of infection, antibiotics or antifungal medications are an option. Some conditions are amenable to surgical intervention such as middle ear fluid, cholesteatoma, and otosclerosis. If conductive hearing loss is due to head trauma, surgical repair is an option. If absence or deformation of ear structures cannot be corrected, or if the patient declines surgery, hearing aids which amplify sounds are a possible treatment option. Bone conduction hearing aids are useful as these deliver sound directly, through bone, to the cochlea or organ of hearing bypassing the pathology. These can be on a soft or hard headband or can be inserted surgically, a bone anchored hearing aid, of which there are several types. Conventional air conduction hearing aids can also be used. See also
Hearing loss
Sensorineural hearing loss

References


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