Imaging Studies
In otosclerosis, fine-cut computed tomography (CT) can often reveal deposition of new bone in the area of the round or oval window and/or otosclerotic foci within other portions of the labyrinthine capsule and cochlea. [5] The outlining of the resultant labyrinth is sometimes referred to as a "halo sign."
Audiometric Testing
Diagnosis depends on a combination of audiometric testing and historical features. [6] An audiometric evaluation reveals conductive hearing loss with absent stapedius reflex. Historically, patients report a relatively slowly progressive hearing loss in the absence of significant infectious ear disease or otologic trauma. Several other indications that can support the diagnosis include the following:
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The Carhart notch (sensorineural hearing loss [SNHL] of 20-30 dB at approximately 2000 Hz) is a frequent audiometric finding in otosclerosis but is also seen in other types of conductive hearing loss; it does not represent genuine SNHL, because it disappears after successful stapedectomy
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Speech discrimination is usually excellent
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A type A tympanogram with very low compliance may be noted; sometimes termed a stiffness curve, this is often referred to as an A S pattern; this configuration is occasionally present but frequently absent
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Fine-cut CT often shows deposition of new bone in the area of the round or oval window and/or otosclerotic foci within other portions of the labyrinthine capsule and cochlea
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Vestibular testing should be included when dizziness is present; although no findings are characteristic for otosclerotic inner ear syndrome, findings suggestive of either superior semicircular canal dehiscence or of Ménière disease alter treatment plans
Audiometric testing is the principal study required for the management of otosclerosis. Both air and bone conduction must be evaluated. If the clinical manifestations are all due to footplate fixation, audiography reveals a purely conductive loss. If involvement of the otic capsule in other areas causes hair cell injury, SNHL is also detected. No explicit criteria have been developed that allow the clinician to definitively distinguish SNHL caused by otosclerosis from hearing loss due to other causes.
Diagnosis of cochlear otosclerosis (ie, SNHL due to otosclerosis) generally requires a halo sign on fine-cut CT or SNHL that is more advanced than expected from presbycusis, in the presence of some sign of stapedial involvement (eg, conductive hearing loss from footplate fixation, abnormalities of stapedius reflex testing).
Histologic Findings
The otospongiotic phase of the disorder is characterized by bone resorption. Several cell types, such as histiocytes, osteocytes, and osteoblasts, participate in this process.
Bone resorption begins around existing vessels with consequent enlargement of vascular channels. Resultant hypervascularization, or a red blush, seen on the medial wall of the inner ear through the tympanic membrane is the Schwartze sign. This hypervascularization can sometimes be visualized during clinical otoscopy.
As the otospongiotic phase continues, a ground substance is deposited as a replacement for resorbed bone. The result is new spongy bone that has a blue appearance on histologic staining. These blue areas seen on hematoxylin and eosin (H&E) preparations are referred to as blue mantles of Manasse.
