2. Middle ear tumor:
There is a wide variety of neoplastic processes
that invade the middle ear. The most common is the
keratoma
(cholesteatoma),
a collection of keratinizing squamous epithelium
that frequently originates from Shrapnell’s membrane (pars
flaccida) of the tympanic membrane or the ear canal wall, and
invades the middle ear space. Other middle ear tumors include
the cholesterol granuloma, glomus tumor, and squamous cell
carcinoma (cf. Goodhill, 1979). These generally result in a flat
tympanogram.
Ossicular fixation.
Ossicular fixation may result from
tympanosclerosis,
a complication
of chronic otitis media that may involve the eardrum, malleus, incus,
and/or stapes, or from otosclerosis, a genetic condition of delayed
onset that produces a focal lesion, immobilizing the stapes footplate.
In general, the more lateral the fixation, the more effect the condition
has on the tympanogram.
1.
Lateral ossicular fixation:
Tympanograms recorded from patients
with lateral ossicular fixation are typically characterized by low
admittance and a wide tympanometric gradient (width).
2.
Otosclerosis:
Because the otosclerotic lesion is more medial
than lateral ossicular fixation, the tympanogram is less affected.
The tympanometric shape is often indistinguishable from normal,
although the static admittance may be slightly low and the
panometric gradient (width) may be narrower than the normal
tympanogram.
