Question
What does it mean when there are two peaks, or a bifid peak on a tympanogram? The results are still within normal range.
Answer
Sounds like a straightforward question but the complete answer lies in the physics of the middle ear. When this was first observed in the 60's and 70's, the focus was on relating this pattern to a middle ear condition, such as ossicular discontinuity. The best answer, provided by a group of physicists at the University of Antwerp, is the Vanhuyse Model (pronounced van-EYES-uh). The model shows that at low frequencies admittance tympanograms from normal adult ears should never be double peaked and at higher frequencies (around 1 kHz and above) they should all be double-peaked. The frequency at which the admittance tympanogram becomes double peaked is roughly equivalent to the resonant frequency of the middle ear. Because our standard 226-Hz probe frequency is remote from the resonant frequency, a double peak at that frequency is never normal (unless you're a newborn infant). When it occurs in anyone older that a few months of age it's an indication of a mass-dominated ear, which can be caused by a decrease in stiffness (thin eardrum or ossicular discontinuity) or an increase in mass (loading of the eardrum or ossicular chain by abnormal tissue like cholesteatoma, granulation, fibrosis, or thick fluid). In the former case, the double-peaked tympanogram is tall and narrow; in the latter case it is broad and flattened. For a more complete discussion see Chapter 17 in Audiology: Diagnosis, Roeser et al (eds) Thieme Medical Publishers, 2000.
Robert H. Margolis, Ph.D., is professor of Audiology in the Department of Otolaryngology at the University of Minnesota.
