Epidermoid cyst

Case contributed by Dr Bruno Di Muzio

Presentation

Right trigeminal neuralgia.

Patient Data

Age: 55 years
Gender: Male

CT Brain

Modality: CT

Non-contrast CT Brain shows a well-defined and lobulated cystic lesion within the medial aspect of the right middle cranial fossa, apparently arising from the right cavernous sinus and showing long-standing features as bone remodeling (best spotted at the petrous apex). Its low attenuation component measures approximately 0 HU. The features can be related to a arachnoid cyst, further evaluation with MRI is advised. 

MRI Brain

Modality: MRI

A large extra-dural mass, bulging into the right middle cranial fossa mass is again demonstrated which likely arises from the right cavernous sinus and Meckel's cave extending inferiorly to surround the right ICA along it segments from C3 to C5 and protrudes into the posterior fossa through the right petroclinoid ligament, involving the trigeminal nerve and bulging the anterolateral aspect of the pons. It is well circumscribed, and has a heterogeneous signal: predominately low on T1, but with some peripheral bright areas, bright on T2 followed by FLAIR suppression, and demonstrating peripheral thin rim of contrast enhancement, representing dura. The lesion shows very bright DWI signal with intermediate ADC (720 x 10-6 mm2/s) and has no elevated relative cerebral blood volume (rCBV). Spectroscopy trace shows a hypometabolic trace. No significant changes were observed compared to the previous exams, considered the limitations of assessing digitized films.

The lesion seems just to compress and displace the adjacent temporal lobe, with no signs of adjacent oedema.

The remainder brain is unremarkable.

Case Discussion

This case illustrates a cystic extradural mass within the right middle cranial fossa are almost pathognomonic of an epidermoid cyst: high T2 signal partially suppressed on FLAIR, intermediate restricted diffusion on ADC and high DWI signal,  and no contrast enhancement. 

The intrinsic T1 and high signal along the medial border is unusual, but likely represents a component of what is referred to as "white epidermoid", recognised variant. The lack of central enhancement, and markedly increased DWI signal makes a chondroid lesion, or cavernous sinus haemangioma much less likely. The absence of a fatty component essentially excludes a dermoid/mature cystic teratoma.

The patient went on to have a resection, which not only confirmed the diagnosis but also confirmed that the lesion was extradural. 

Histology

MICROSCOPIC DESCRIPTION:  Paraffin sections show multiple fragments of laminated keratin consistent with the contents of an epidermal cyst. No hair remnants or mesenchymal elements are seen. No cyst lining is identified.

FINAL DIAGNOSIS: Contents of epidermal cyst.

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Case Information

rID: 39743
Case created: 18th Sep 2015
Last edited: 28th Feb 2017
Tag: rmh
Inclusion in quiz mode: Included

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