Tympanometry and tympanogram types

What tympanometry measures

Tympanometry, also written impendence audiometry, is part of the impendence test, and it is used to measure the efficiency of the middle ear.

Every trace is read off two axes, and both are named on the page:

• One of them is tympanic membrane compliance, marked from 200 to 1400.
• The other is middle ear pressure, marked from -400 to +200.

So two things are read from any tympanogram: the compliance at the peak, and the pressure at which the peak sits.

The five curves

• Type A: the normal tympanogram, a peak at or near zero pressure. It is also the trace of sensorineural hearing loss, where the conductive mechanism is normal - so a normal tympanogram is not the same as normal hearing.
• Type B: a flat curve, with no change in compliance as the pressure changes. Seen with fluid in the middle ear, that is otitis media with effusion. The same flat trace is described as a retracted tympanic membrane or a poorly mobile drum.
• Type C: the peak sits on the negative side, because of negative middle ear pressure. Seen with a retracted tympanic membrane, most likely ET obstruction due to allergies or URTI, and in early otitis media and eustachian tube obstruction.
• Type As: a small peak. Compliance is lower at or near ambient pressure, and it is seen in otosclerosis or malleus fixation, described also as ossicular fixation or TM perforation. The page notes the point that matters: the pressure is normal but the compliance is low.
• Type Ad: the peak increases. High compliance at or near ambient pressure, seen in ossicular discontinuity, described also with TM perforation. Again the pressure is normal, but here the compliance is high.