Audiometry

Otosclerosis can be familial, particularly  when it  is severe. It results  from fibrous ankylosis followed by bony overgrowth of the little ossicles of the middle car. A schwannoma typically  involves  the  eighth cranial nerve and results in  a  nerve  conduction form  of  deafness. Schwannomas are usually unilateral. although familial neurofibromatosis could result in the appearance of multiple schwannomas. A cholesteatoma is typically a unilateral process that complicates  chronic  otitis  media  in  a  child  or young adult otitis media by itself is usually self- limited and uncommon in an adult Chondrosarcomas may involve the skull in older adults but are rare and are solitary bulky masses in the region of the jaw.

The threshold of bone conduction is a measure of cochlear function in pure tone audiometry.

The difference in the thresholds of air and bone conduction (A-B) is a measure of the degree of conductive deafness.

Here this patient is having a normal cochlear function.

So A-B gap of 55 dB will be because of defect in air conduction.

Otoscopic examination showed an intact tympanic membrane means the ossicular discontinuity will be the reason for the hearing loss.

Pure tone audiometry is a subjective test used in the assessment of hearing in a patient presenting with impairment in hearing. 

• It is a subjective, behavioural measurement of hearing threshold enabling determination of degree, type, and configuration of any hearing loss.
• The test can provide both bone and air conduction threshold.
• The frequency range tested includes 250Hz to 8kHz.
• The threshold of lower limit of normal is considered to be 20dB.
• 30dB equates to the threshold of a whispered voice at 2 feet from the ear, 60dB a conversational voice, and 100dB a pneumatic drill in the street.

Bekesy audiometry:

• Type I: Continuous and pulsed tracings overlap. Seen in normal hearing or conductive hearing loss.
• Type II: Continuous and pulsed tracings overlap up to 1000 Hz and then continuous tracing falls. Seen in cochlear loss.
• Type III: Continuous tracing falls below pulsed tracing at 100 to 500 Hz even up to 40-50 dB. Seen in retrocochlear/neural lesion.
• Type IV: Continuous tracing falls below pulsed lesion at frequencies up to 1000 Hz by more than 25 dB. Seen in retrocochlear/neural lesion.
• Type V: Continuous tracing is above pulsed one. Seen in non-organic hearing loss.

High-frequency audiometry is specifically for ototoxicity monitoring, comprises air conduction thresholds from 10,000 to 20,000 Hz.

 Most ototoxic hearing losses will first occur in that frequency region, which is higher than the speech range. 

Otosclerosis is characterized by abnormal removal of mature dense otic capsule bone by osteoclasts, and replacement with the woven bone of greater thickness, cellularity, and vascularity.

When disease involves the annular ligament of the oval window and stapes footplate, a conductive hearing loss (CHL) occurs which is slowly progressive, usually bilateral and asymmetric. 

Pure tone audiometry gives information about the quantity and quality of hearing loss.

In secretory otitis media: conductive deafness of 20-40 dB is seen (which is not a specific finding as conductive deafness can be seen in many other conditions). Therefore, pure tone audiometry is not diagnostic of serous otitis media but provides an assessment of the hearing loss and is therefore important in monitoring the progress of the condition and provides information useful for management decisions

On otoscopy: Tympanic membrane appears dull, opaque with loss of light reflex

X-ray mastoid: Shows clouding of air cells. (not diagnostic)

Impedance audiometry is an accurate way of diagnosing serous otitis media. It shows type B tympanogram which is diagnostic of fluid in ear.