Reviewed by Afsaneh Khetrapal BSc (Hons)
Sound waves pass from the ear canal in the outer ear to the middle ear, and create a vibration of the eardrum. Due to the vibrations of the tiny bones in the middle ear, we are able to hear sound. When there is a lack of vibration, it affects hearing and we term this condition as conductive hearing loss. There will be a reduction in the sound levels and the patient may not be able to hear faint founds. Conductive hearing loss is a problem connected with the outer ear or middle ear, or both.
Problems Associated with Outer Ear
Impacted ear wax: When ear wax, or cerumen, accumulates in the ear, it can cause temporary conductive hearing loss. After medical examination, this can be removed quickly.
Otitis Externa (swimmer’s ear): When a person is exposed to water, there could be an infection in the ear canal and the patient could feel pain and tenderness in the ear resulting from bacterial or fungal infection. However if there is severe swelling in the ear canal, conductive hearing loss may occur.
The presence of foreign bodies such as beads, beans, tips of cotton-tipped applicators in the ear canal can cause itching and pain.
The growth of benign tumors along the ear canal walls result in narrowing of the ear canal. The mass effect of the tumor will then block the transmission of sound in the middle ear. Usually cleaning the ear wax will help, however, in rare instances lesions have to be removed surgically.
External auditory canal atresia: At the time of birth, some individuals may be seen with partial or complete malformation of the outer ear. The external auditory canal is absent or closed, resulting in conductive hearing loss. For some individuals, reconstructing the ear canal surgically will help or devices are fixed to create vibrations in the ear.
Problems Associated with Middle Ear
When an infection such as a cold produces mucus in the middle ear, most middle-ear infections occur. This makes the thin eustachian tube swell or creates a blockage, preventing the mucus from draining, making it easy for the infection to spread in the middle ear.
Otitis media is a condition in which the middle ear is filled up with fluid. Acute otitis media is painful and often followed by serous otitis media infection. Chronic conditions of otitis media may create damage to the eardrum or middle ear bones. Myringotomy surgery helps to treat otitis media.
When the adenoid tissue traps bacteria and viruses, sometimes they become infected and this results in enlarged adenoids, while sometimes they can also block the eustachian tube creating problems in the middle ear. Poor function of the eustachian tube creates excessive negative pressure behind the eardrum and collapses the eardrum onto the middle ear bones, leading to tympanic membrane atelectasis. Tympanoplasty or ear tube correction surgery will benefit patients.
Tympanometry tests measure the eardrum movement and create graphs called tympanograms. These can help diagnose problems with the middle ear such as a stiff eardrum, a hole in the eardrum and accumulation of fluid in the middle ear.
Due to infections or trauma, there is a possibility of a perforation in the tympanic membrane. Damaged eardrums cannot capture sound vibrations effectively as the middle ear ossicles are damaged in these conditions. Surgical treatment of the ossicular chain is beneficial.
Due to abnormal bone remodeling (otosclerosis) in the middle ear, there is disruption in sound traveling from the middle to the inner ear and this results in impaired hearing. Women are more prone to this than men and the hearing loss gradually progresses in early adulthood. For mild hearing loss, patients can use hearing aids to increase the sound reaching the eardrum.
Stapedectomy surgery is very effective in resolving these conditions. In this process, a part or all of the immobile stapes bones are removed and replaced with a prosthetic device that allows the bones of the middle ear to function, thereby improving or restoring hearing.
Conditions such as cholesteatoma, abnormal skin growth behind the eardrum in the middle ear, may lead to conductive hearing loss. Physicians have to perform multiple surgeries to remove the cholesteatoma. By repairing the damaged middle ear bones, hearing can be restored.
Third Window Abnormalities (Inner Ear)
The role of the third window pathways, such as the vestibular aqueduct, cochlear aqueduct, and foramina for blood vessels, is said to be small in the auditory process. However third window lesions such as dehiscence of superior, posterior, and lateral canals, enlarged vestibular aqueduct syndrome(EVAS), X-linked stapes gusher), perilabyrinthine fistula, dehiscence between cochlea and carotid canal, and bone dyscrasias result in conductive hearing loss.
There are two windows between the middle and inner ear, oval and round windows, through which sound is transmitted. When there is a third window, the acoustic energy from the oval window is shunted and the transmission to the round window is decreased. The hair cells receive less acoustic energy and so the perception of the sound is reduced.
Reviewed by Afsaneh Khetrapal BSc (Hons)