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What is the difference between conductive and sensorineural hearing loss?

Conductive deafness is caused by failure of transmission of sound waves across the outer or middle ear. This prevents sound energy from reaching the cochlear fluid.

Sensorineural hearing loss is caused by defective function of the cochlear or the auditory nerve. This prevents nerve impulses being transmitted to the auditory cortex of the brain.


Is it possible to distinguish between conductive and sensorineural hearing loss on examination?

Yes. Rinne and Weber's tests (or tuning fork tests) can help distinguish between the two.

Rinne's test should be performed first but will tell you nothing about cochlear function, it only tests the middle ear. A 512Hz tuning fork is held close to the patients ear and then on the mastoid process. The patient is asked which from the air (AC) or bone (BC) is louder.

If AC>BC this is POSITIVE and shows a normal middle ear.
If BC > AC this is NEGATIVE and means there is defective function of the outer or middle ear (conductive deafness).

Weber's test is helpful in distinguishing the type of deafness and deciding which ear has better cochlear function. The base of the tuning fork is held on the middle of the skull and the patient is asked whether the sound is heard centrally or is referred to one or other other ear.

In conductive deafness the sound is heard in the deafer ear (abnormal one).
In sensorineural deafness the sound is heard in the better- hearing ear (normal).


A patient has a positive Rinne's test in both ears and the Weber test is referred to the left ear. What type of hearing loss is present?

Positive Rinne's test in both ears shows there is no conductive hearing loss - i.e. AC>BC for both, indicating normal middle ear function. In sensorineural hearing loss the sound refers to the good ear so the patient has a right sided sensorineural hearing loss.

The key hear is that Rinne's test is positive in both ears, showing that there can be no conductive loss.


A patient has a negative Rinne test on the right and a positive one on the left. They also have a Weber test that refers to the right ear. What type of hearing loss is present?

Firstly, a negative Rinne test indicates that there is a conductive hearing problem. BC>AC on the right ear shows that there is an abnormal middle ear on the right side. Weber test refers to the affected ear in conductive hearing loss so this patient has conductive deafness on the right side.


Name some common causes of conductive hearing loss?

- wax
- acute otitis media
- barotrauma
- osteosclerosis
- injury of the tympanic membrane

NB - rarer causes are mostly congenital


Name some common causes of sensorineural deafness?

- presbycusis (deafness in old age)
- noise induced (prolonged exposure)
- congenital (meternal rubella, CMV, anoxia, jaundice)
- drug induced (aminoglycosides, diuretics)
- Meniere's disease
- infection (chronic otitis media, mumps etc)


What is the commonest cause of deafness in children?

The commonest cause of deafness in children is fluid in the middle ear due to otitis media. This causes a temporary conductive deafness.

Sensorineural loss is rare but when it does occur it is usually permanent.

NB - early identification can greatly improve outcome


What babies are "at risk" of deafness and should be tested as soon after birth as possible?

1) prematurity and low birth weight
2) perinatal hypoxia
3) Rhesus disease
4) family history of hereditary deafness


How should sudden sensorineural deafness be managed?

Sudden deafness may be unilateral or bilateral and most cases are regarded as being viral or vascular. Sudden onset sensorineural hearing loss is an emergency and warrants hospital admission.


What is an acoustic neuroma? When are they bilateral?

Despite being called a neuroma, acoustic neuromas are actually a Vestibular Schwannoma. They are benign tumours in the internal auditory meatus or cerebello-pontine angle at the base of the skull.

They are usually unilateral except in rare familial neurofibromatosis type 2.

In the early stages it causes progressive hearing loss and imbalance. As it gets bigger, it may compress the trigeminal nerve in the CP angle and cause loss of corneal sensation. Advanced stages are associated with raised ICP and brainstem displacement. MRI is the best modality to view them.


In what type of deafness are cochlear implants suitable?

Bilateral profound deafness.


What are "protruding ears"?

These are protrusions in the ear caused by the absence of the ante helical fold in the auricular cartilage. Surgical correction can be carried out after the age of four. This consists of exposing the lateral aspect of the cartilage from behind the pinna and scoring it to produce a rounded fold.


What is an accessory auricle? Where are they usually found?

These are small tags often containing cartilage on a line between the angle of the mouth and the tragus.


What is a pre-auricular sinus?

Pre-auricular sinus is a small blind pit that occurs most commonly anterior to the root of the helix. It is sometimes bilateral and may be familial.

If they become recurrently infected they are best removed surgically.


What is microtia? What is it associated with? What is Treacher Collins syndrome?

Microtia is failure of the development of the pinna.
It may be associated with atresia of the ear cannal.

Treacher Collins syndrome is associated with absence or severe malformation of the external ear. Patients can be treated with a bone anchored hearing aid (BAHA) and then a prosthetic ear.


Why does a subperichondrial haematoma cause cauliflower ear if left untreated?

Haematoma of the pinna is usually caused by shearing forces. The pinna gets ballooned and the outline of the cartilage is lost.

The blood supply of the cartilage comes from the perichondrium so an untreated haematoma will cause severe deformity - a cauliflower ear.

Treatment consists of evacuating the clot and reapposition of cartilage and perichondrium by pressure drainage.


What is the usual cause of acute dermatitis affecting the pinna?

This is usually caused by extension of meatal infection in otitis externa or sensitivity reaction to topically applied antibiotics, especially chloramphenicol and neomycin.

The golden rule of treatment here is that if otitis externa gets worse following treatment then it is usually due to a sensitivity reaction and antibiotics should be stopped.


What causes perichondritis of the pinna?

Perichondritis ("inflammation of the perichondrium") may follow injury to the cartilage, mastoid surgery or ear piercing.

Treatment must be vigorous with parenteral antibiotics. Piercings should be removed.


What malignancies occur on the pinna?

Both squamous cell carcinoma and basal cell carcinoma can occur on the pinna, usually the upper edge. They are related to exposure to sunlight.

Chondrodermatitis chronicis helicis occurs in the elderly as a painful ulcerated lesion on the rim of the helix. It resembles a neoplasm and should be removed for histology.


What glands produce wax in the ear and how should impacted wax be treated?

Wax is produced by ceruminous glands in the outer ear. When it is produced it migrates along the meatus laterally. Because of this, ears are "self cleaning".

Impacted wax can cause irritation or conductive hearing loss, and is best treated by syringing.


What solution is used for waxing and what is the technique involved?

Sodium bicarbonate 4-5g to 500ml or normal saline is ideal. The temperature of the solution is important and should be 38 degrees so it does not cause dizziness.

The stream of the solution should be directed along the roof of the external auditory canal.


What is otitis externa?

This is diffuse inflammation of the skin lining the outer ear canal. It may be bacterial or fungal.

Symptoms include:
1) irritation
2) discharge
3) pain (usually moderate, sometimes severe, increased by jaw movement)
4) deafness (mild)

Signs include meatal tenderness, especially on movement of the pinna or compression of the tragus; and moist debris which when removed shows red, desquamated skin and oedema of the meatal walls and tympanic membrane.


What causes otitis externa?

Some patients are prone to otitis externa - e.g. narrow external canal, bathing in hot climates, exposure to swimming pools, underlying skin diseases (eczema or psoriasis).

A mixed infection of varying organisms is typical, the most common are:
- pseudomonas
- staph
- diptherioids
- proteus
- strep faecalis
- aspergillus niger (black spores are often visible)


What is the management of otitis externa?

The key to managing otitis externa is good aural toilet - clean the debris and keep the ear clean and dry. No medication will be effective if the ear is full of debris and pus. Aural toileting is best performed using dry mopping with cotton wool - don't miss the antero-inferior recess which may be difficult to clean.


When should dressings be used in otitis externa? What should you suspect if the patients condition has not improved after 7-10 days?

Dressings can be used if otitis externa is severe and has not responded to good aural toileting. Gauze impregnated with medication is gently inserted into the meatus and is changed daily until the meatus has returned to normal.

If after 7-10 days of regular dressing changes the meatus has not improved then re check the tympanic membrane. This could be a case of otitis media with discharging perforation of the membrane which will not heal with dressings alone.


What medications can be useful for treating otitis externa? What antibiotics can be used if otitis externa is less severe?

The following medications are useful on dressings:
- 80% aluminium acetate
- 10% ichthammol in glycerine
- ointment of gramicidin, neomycin, nystatin and triamcinolone

In fungal otitis externa use dressings of 3% amphoteracin, miconazole or nystatin.

If otitis externa is less severe and there is little meatal swelling it may respond to a combination of antibiotic and steroid drops. Antibiotics most commonly used are neomycin and gramicidin but there is a worry with putting aminoglycosides into the inner ear as they can cause deafness. Use ciprofloxacin drops if you suspect a perforated tympanic membrane.


What is furunculosis?

This is a "boil" of the external canal resulting from infection of a hair follicle in the lateral part of the meatus. Staph is the usual organism.

Symptoms - pain is as severe as that of renal colic; pain is made much worse by movement of the pinna or pressure on the tragus. Deafness is usually mild and caused by meatal occlusion by the furuncle.

Signs - there is often no visible lesion but use of a speculum causes intense pain. If the faruncle is large it will be seen as a red swelling in the outer meatus and there may be more than one faruncle present.


How is furunculosis treated?

In advanced stages the furuncle may cause an abscess so antibiotic treatment is required. Firstly, a wick soaked in 10% ichthammol in glycerine is inserted. This painful but provides rapid relief.

Flucloxacillin is given parenterally for 24h followed by oral medication. Analgesics are essential.

Recurrent cases are not common so exclude diabetics and take a nasal swab in case the patient is a recurrent staph carrier.


What are exostoses?

These are bony outgrowths or small osteomata of the external auditory meatus. They are fairly common and usually bilateral and are much more common in those who swim a lot in cold water but the reason for this is not clear.

There may be two or three small tumours arising in each bony meatus. They are hard, smooth and very sensitive to touch. They tend to grow slowly and may give rise to no symptoms.


How can the tympanic membrane become damaged?

The tympanic membrane is well protected but can be injured by direct or indirect trauma:
- direct trauma is caused by poking the ear with a sharp implement such as hair grips in an attempt to clean the ear, or foreign bodies

- indirect trauma is usually caused by pressure from a slap with an open hand or from a blast injury; it may occur from temporal bone fracture in a severe head injury