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Epidermoid cyst

Case contributed by Ammar Haouimi
Diagnosis almost certain

Presentation

Epilepsy.

Patient Data

Age: 30 years
Gender: Female
mri

Extra-axial mass centered on the right crural cistern extending inferiorly to the cerebellopontine angle with intracanalicular extension as well as to the prepontine and suprasellar cisterns. It encases the facial/vestibulocochlear nerves, and compressing the cisternal portion of the ipsilateral trigeminal nerve. It displays a low signal on T1, heterogeneous signal on FLAIR and high signal on T2 with restricted diffusion and no enhancement seen on the postcontrast sequence.

Case Discussion

MRI features most consistent with an epidermoid cyst centered on the crural cistern, extending to the cerebellopontine angle with intracanalicular extension as well as to the suprasellar and prepontine cisterns compressing the cisternal portion of the ipsilateral trigeminal nerve.

DWI is important to differentiate an epidermoid cyst from an arachnoid cyst (the arachnoid cyst follows the CSF signal on all sequences with no restricted diffusion).

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