Conductive hearing loss

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Conductive hearing loss
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Anatomy of the human ear.
Specialty ENT surgery

Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). If a conductive hearing loss occurs in conjunction with a sensorineural hearing loss, it is referred to as a mixed hearing loss. Depending upon the severity and nature of the conductive loss, this type of hearing impairment can often be treated with surgical intervention or pharmaceuticals to partially or, in some cases, fully restore hearing acuity to within normal range. However, cases of permanent or chronic conductive hearing loss may require other treatment modalities such as hearing aid devices to improve detection of sound and speech perception. [1]

Contents

Causes

Common causes of conductive hearing loss include: [2]

External ear

Middle ear

Fluid accumulation is the most common cause of conductive hearing loss in the middle ear, especially in children. [3] Major causes are ear infections or conditions that block the eustachian tube, such as allergies or tumors. [3] 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. [4]

Inner ear

Third window effect caused by:

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. Conductive hearing loss developing during childhood is usually due to otitis media with effusion and may present with speech and language delay or difficulty hearing. Later onset of conductive hearing loss may have an obvious cause such as an ear infection, trauma or upper respiratory tract infection or may have an insidious onset related to chronic middle ear disease, otosclerosis or a tumour of the naso-pharynx. Earwax is a very common cause of a conductive hearing loss which may present suddenly when the wax blocks sound from getting through the external ear canal to the middle and inner ear.

Diagnosis

Diagnosis requires a detailed history, local examination of the ear, nose, throat and neck, and detailed hearing tests. In children a more detailed examination may be required if the hearing loss is congenital.

Otoscopy

Examination of the external ear canal and ear drum is important and may help identify problems located in the outer ear up to the tympanic membrane.

Differential testing

For basic screening, a conductive hearing loss can be identified using the Rinne test with a 256 Hz tuning fork. The Rinne test, in which a patient is asked to say whether a vibrating tuning fork is heard more loudly adjacent to the ear canal (air conduction) or touching the bone behind the ear (bone conduction), is negative indicating that bone conduction is more effective that air conduction. A normal, or positive, result, is when air conduction is more effective than bone conduction.

With a one-sided conductive component the combined use of both the Weber and Rinne tests is useful. If the Weber test is used, in which a vibrating tuning fork is touched to the midline of the forehead, the person will hear the sound more loudly in the affected ear because background noise does not mask the hearing on this side.

The following table compares sensorineural hearing loss to conductive:

CriterionSensorineural hearing lossConductive hearing loss
Anatomical site Inner ear, cranial nerve VIII, or central processing centers Middle ear (ossicular chain), tympanic membrane, or external ear
Weber test Sound localizes to normal earSound localizes to affected ear (ear with conductive loss)
Rinne test Positive Rinne; air conduction - bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged).Negative Rinne; bone conduction - air conduction (bone/air gap)

Tympanometry

Tympanometry, or acoustic immitance testing, is a simple objective test of the ability of the middle ear to transmit sound waves from the outer ear to the middle ear and to the inner ear. This test is usually abnormal with conductive hearing loss. A type B tympanogram reveals a flat response, due to fluid in the middle ear (otitis media), or an eardrum perforation. [5] A type C tympanogram indicates negative middle ear pressure, which is commonly seen in eustachian tube dysfunction. [5] A type As tympanogram indicates a shallow compliance of the middle ear, which is commonly seen in otosclerosis. [5]

Audiometry

Pure tone audiometry, a standardized hearing test over a set of frequencies from 250 Hz to 8000 Hz, may be conducted by a medical doctor, audiologist or audiometrist, with the result plotted separately for each ear on an audiogram. The shape of the plot reveals the degree and nature of hearing loss, distinguishing conductive hearing loss from other kinds of hearing loss. A conductive hearing loss is characterized by a difference of at least 15 decibels between the air conduction threshold and bone conduction threshold at the same frequency. 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. [1]

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. [6] 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. [3] 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

Related Research Articles

This is a glossary of medical terms related to communication disorders which are psychological or medical conditions that could have the potential to affect the ways in which individuals can hear, listen, understand, speak and respond to others.

<span class="mw-page-title-main">Middle ear</span> Portion of the ear internal to the eardrum, and external to the oval window of the inner ear

The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea.

<span class="mw-page-title-main">Cholesteatoma</span> Medical condition

Cholesteatoma is a destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process. Cholesteatomas are not cancerous as the name may suggest, but can cause significant problems because of their erosive and expansile properties. This can result in the destruction of the bones of the middle ear (ossicles), as well as growth through the base of the skull into the brain. They often become infected and can result in chronically draining ears. Treatment almost always consists of surgical removal.

<span class="mw-page-title-main">Eardrum</span> Membrane separating the external ear from the middle ear

In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in the air to vibration in cochlear fluid. The malleus bone bridges the gap between the eardrum and the other ossicles.

<span class="mw-page-title-main">Otitis media</span> Inflammation of the middle ear

Otitis media is a group of inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, increased crying, and poor sleep. Decreased eating and a fever may also be present. The other main type is otitis media with effusion (OME), typically not associated with symptoms, although occasionally a feeling of fullness is described; it is defined as the presence of non-infectious fluid in the middle ear which may persist for weeks or months often after an episode of acute otitis media. Chronic suppurative otitis media (CSOM) is middle ear inflammation that results in a perforated tympanic membrane with discharge from the ear for more than six weeks. It may be a complication of acute otitis media. Pain is rarely present. All three types of otitis media may be associated with hearing loss. If children with hearing loss due to OME do not learn sign language, it may affect their ability to learn.

<span class="mw-page-title-main">Eustachian tube</span> Tube connecting middle ear to throat

In anatomy, the Eustachian tube, also known as the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately 35 mm (1.4 in) long and 3 mm (0.12 in) in diameter. It is named after the sixteenth-century Italian anatomist Bartolomeo Eustachi.

<span class="mw-page-title-main">Otosclerosis</span> Condition characterized by an abnormal bone growth in the middle ear

Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone. As the lesions reach the stapes the bone is resorbed, then hardened (sclerotized), which limits its movement and results in hearing loss, tinnitus, vertigo or a combination of symptoms. The term otosclerosis is something of a misnomer: much of the clinical course is characterized by lucent rather than sclerotic bony changes, so the disease is also known as otospongiosis.

<span class="mw-page-title-main">Hearing test</span> Evaluation of the sensitivity of a persons sense of hearing

A hearing test provides an evaluation of the sensitivity of a person's sense of hearing and is most often performed by an audiologist using an audiometer. An audiometer is used to determine a person's hearing sensitivity at different frequencies. There are other hearing tests as well, e.g., Weber test and Rinne test.

<span class="mw-page-title-main">Ear</span> Organ of hearing and balance

An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone. The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localization.

<span class="mw-page-title-main">Weber test</span> Screening test for hearing

The Weber test is a screening test for hearing performed with a tuning fork. It can detect unilateral (one-sided) conductive hearing loss and unilateral sensorineural hearing loss. The test is named after Ernst Heinrich Weber (1795–1878). Conductive hearing ability is mediated by the middle ear composed of the ossicles: the malleus, the incus, and the stapes. Sensorineural hearing ability is mediated by the inner ear composed of the cochlea with its internal basilar membrane and attached cochlear nerve. The outer ear consisting of the pinna, ear canal, and ear drum or tympanic membrane transmits sounds to the middle ear but does not contribute to the conduction or sensorineural hearing ability save for hearing transmissions limited by cerumen impaction.

The Rinne test is used primarily to evaluate loss of hearing in one ear. It compares perception of sounds transmitted by air conduction to those transmitted by bone conduction through the mastoid. Thus, one can quickly screen for the presence of conductive hearing loss.

<span class="mw-page-title-main">Facial nerve paralysis</span> Medical condition

Facial nerve paralysis is a common problem that involves the paralysis of any structures innervated by the facial nerve. The pathway of the facial nerve is long and relatively convoluted, so there are a number of causes that may result in facial nerve paralysis. The most common is Bell's palsy, a disease of unknown cause that may only be diagnosed by exclusion of identifiable serious causes.

Audiometry is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and otoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram.

<span class="mw-page-title-main">Tympanometry</span>

Tympanometry is an acoustic evaluation of the condition of the middle ear eardrum and the conduction bones by creating variations of air pressure in the ear canal.

<span class="mw-page-title-main">Perforated eardrum</span> Injury leading to a hole in the eardrum

A perforated eardrum is a hole in the eardrum. It can be caused by infection, trauma, overpressure, inappropriate ear clearing, and changes in middle ear pressure. An otoscope can be used to view the eardrum to diagnose a perforation. Perforations may heal naturally, or require surgery.

Hearing loss with craniofacial syndromes is a common occurrence. Many of these multianomaly disorders involve structural malformations of the outer or middle ear, making a significant hearing loss highly likely.

<span class="mw-page-title-main">Tympanosclerosis</span> Medical condition

Tympanosclerosis is a condition caused by hyalinization and subsequent calcification of subepithelial connective tissue of the tympanic membrane and middle ear, sometimes resulting in a detrimental effect to hearing.

<span class="mw-page-title-main">Tympanic membrane retraction</span> Medical condition

Tympanic membrane retraction describes a condition in which a part of the eardrum lies deeper within the ear than its normal position.

<span class="mw-page-title-main">Diagnosis of hearing loss</span>

Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician or otorhinolaryngologist.

A middle ear implant is a hearing device that is surgically implanted into the middle ear. They help people with conductive, sensorineural or mixed hearing loss to hear. 

References

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  2. "Hearing Loss". HealthCentral. Retrieved 8 June 2013.
  3. 1 2 3 Ruben, Robert J. (April 2007). "Hearing Loss and Deafness". The Merck Manual. Retrieved 8 June 2013.
  4. 1 2 Page 152 in:Rex S. Haberman (2004). Middle Ear and Mastoid Surgery. New York: Thieme Medical Pub. ISBN   1-58890-173-4.
  5. 1 2 3 Onusko, Edward M. (2004-11-01). "Tympanometry". American Family Physician. 70 (9): 1713–1720. ISSN   0002-838X. PMID   15554489.
  6. "Types, Causes and Treatment". Hearing Loss Association of America. Retrieved 8 June 2013.