Perilabyrinthine intraosseous epidermoid cyst
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Presents with gradually developing right facial palsy.
There is well-defined T2WI heterogeneously hyperintense and T1WI isointense lesion in right petrous temporal bone, superior to the vestibulocochlear apparatus showing partial suppression of signals on FLAIR image. Lesion shows restricted diffusion (bright signals on DWI with corresponding iso- to hypointense signal on ADC). No significant post-contrast enhancement noted.
The lesion is causing erosion of superior and posterior semicircular canals with obliteration of CSF intense signals within the semicircular canals. Inferiorly, the lesion is bulging into lateral third of right internal auditory canal causing compression and inferior displacement of the 7th-8th nerve complex.
A right mastoid effusion is noted.
Axial bone window images of right petrous temporal bone showing an expansile lytic lesion, superior to the vestibulocochlear apparatus resulting in severe thinning and erosions of superior wall of the petrous temporal bone. The lesion is also causing focal erosion of the superior and posterior semicircular canals and the labyrinthine segment of facial nerve canal.
The cochlea, vestibule and the inferior semicircular canal are normal.
1 case question available
Constellation of MRI imaging features of an expansile non-enhancing lesion in mid portion of right petrous temporal bone showing T2w hyperintense signals with partial suppression of signal on FLAIR imaging and with restricted diffusion are consistent with a perilabyrinthine epidermoid cyst (classical imaging features of epidermoid cyst).
Our patient had a right facial palsy secondary to erosion of labyrinthine segment of facial nerve canal by the expansile, lytic lesion.
An intraosseous location, especially in a perilabyrinthine location is a rare site of epidermoid cysts. However, they show similar MRI imaging features as elsewhere in the body. The close proximity of the lesion to the vestibulocochlear apparatus can lead to symptoms related to facial palsy, balancing problems and hearing impairment.