Labyrinthine schwannoma

Case contributed by Chris O'Donnell
Diagnosis almost certain

Presentation

Sudden right-sided hearing loss 7 years ago. Initial MRI 6 years ago. Thought to be labyrinthitis. No improvement and now vertigo for follow-up.

Patient Data

Age: 70 years
Gender: Male

Original MRI 6 years ago

mri

Subtle but definite asymmetrical enhancement of the right basal turn of the cochlea and modiolus.

Follow-up MRI 6 years later

mri

Mass lesion with abnormal enhancement involving the cochlea, vestibule and components of the VIIIth nerve at the apex of the internal auditory canal.

Case Discussion

Most "acoustic' schwannomas arise in the vestibular nerve at the vestibular ganglion that is at the junction of the central and peripheral myelin (in the fundus of the IAC). Schwannomas can actually occur anywhere along the canal where there are Schwann cells supporting peripheral myelin but can involve the membranous labyrinth i.e. cochlea, vestibule, or semicircular canals where there are also peripheral nerves.  These are known as labyrinthine schwannomas and are quite rare.

In this case, the very early finding of enhancement without mass effect in the modiolus and basal turn of the cochlea has been interpreted as an inflammatory process but over time the true tumourfactive nature of a schwannoma has been revealed.

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