Ziyad Almushayti and Husam Almuhaish of Qassim University, Saudi Arabia report a case of an unusual epidermoid cyst in cerebellopontine angle that appeared hyperdense on computed tomography (CT) scanning, hyperintense on T1-weighted MR images and hypointense on T2/ FLAIRweighted magnetic resonance (MR) images. A non enhanced CT scan examination of brain of the 50 year old patient was performed which revealed a hyperdense extra-axial right cerebellopontine lesion measuring 26.5 × 15.5 mm, causing mild mass effect to adjacent structures.
The right cerebellopontine lesion revealed no significant enhancement, T1W images showed a well-defined extra axial homogeneous hyperintense lesion in right cerebellopontine cistern and T2/ FLAIR weighted magnetic resonance (MR) images shows a well -defined lobulated hypointense extraxial mass on right cerebellopontine cistern. Post-contrast fatsuppressed T1-W spin-echo sequence shows no enhancement with persistent pre contrast hyperintense signal intensity.
Scientific literature provided by Timmer et al. explains these unusual features on CT and MRI by high protein concentration and high viscosity. Timmer attributes the high signal intensity seen on T1-weighted imaging to the relatively high protein concentration of the cystic contents (>90 mg/l). The low signal on T2- weighted images can be explained by the high viscosity of the fluid. In this case reported by Almushayti and Almuhaish, the epidermoid cyst was dense on CT scans and the unusual MR characteristics is explained by a combination of very high protein concentration and high viscosity.