Epidermoid cyst - middle cranial fossa

Case contributed by Frank Gaillard
Diagnosis certain



Patient Data

Age: 20 years
Gender: Female

A fluid/CSF density lesion / space is located in the middle cranial fossa displacing adjacent right temporal and frontal lobe. 

A 4.1 x 3.8 x 3.3 cm extra-axial right anterior temporal lesion is again demonstrated, stable in size and morphology. This has features consistent with an epidermoid, with high T2 signal, incomplete FLAIR suppression and diffusion restriction, similar to adjacent white matter.

The lesion has a mass effect on the adjacent right temporal and inferior frontal lobes, with the right amygdala displaced superiorly. It abuts the temporal horn of the right lateral ventricle. The right hippocampus is slightly larger than the left, with preserved internal architecture - possibly postictal in nature.

Elsewhere no further lesions are identified.


Large right middle cranial fossa epidermoid, which exerts mild mass-effect upon the adjacent temporal and inferior frontal lobes as well as resulting in displacement of the right amygdala.


The patient went on to have resection of the lesion. 


The sections show predominantly aggregation of laminated keratin. Short segments of a membrane composed of a lining of squamous epithelium arranged on a thin layer of collagen are noted. The squamous epithelium fas a well developed granular layer. The overall features are of an epidermal cyst. No appendageal structures are identified. There is no evidence of tumor.


Epidermal cyst.

Case Discussion

This is a wonderful exam case, as the location of the epidermoid is more typical of its main CT differential - an arachnoid cyst. Still, the imaging is obviously that of an epidermoid cyst, particularly of DWI / ADC, with the content demonstrating ADC values similar to white matter (~700 x 10-6 mm2/s). 

On follow-up imaging, the hippocampal signal on the right had returned to normal confirming that this was indeed post-ictal. 

How to use cases

You can use Radiopaedia cases in a variety of ways to help you learn and teach.

Creating your own cases is easy.

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.