Internal auditory canal exostoses

Case contributed by Carlos García-Moncó Fernández
Diagnosis almost certain


Bilateral mixed hearing loss, more important on the left side. Tinnitus.

Patient Data

Age: 55 years
Gender: Female

There is a prominent broad-based osseous growth of the posterior and superior opening of the left internal auditory canal (IAC) resulting in a narrowing of the left porus acoustics. On the right side there is a less prominent bone growth with similar characteristics, mildly abutting the right IAC.

MRI shows T2 hypointense bony growth in the porus of the left internal auditory canal narrowing its lumen. There is a similar but smaller lesion on the right side.

Case Discussion

We can see there is a lesion in the porus of the left internal auditory canal and a smaller one on the right side. Its signal is similar to that of the bone and it does not show any contrast enhancement, so we know it is not a schwannoma, but rather a bony lesion. There is not a generalized bone involvement, so it does not look like Paget disease or fibrous dysplasia.

We are left mainly with two options: exostoses vs osteomas. Osteomas are usually pedunculated, unilateral, and show some bone marrow inside, as a sign of fibrovascular channels running inside them.

Our patient had mild to moderate symptoms, so she was managed conservatively. Surgery is only considered in severe cases with nerve deficits, which is why we usually do not get a histologic confirmation in these cases.

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