Imaging findings are consistent with a pineal region epidermoid cyst.

This particular case was challenging to diagnose on conventional MR sequences. It was however readily identified on high-resolution T1 and T2-weighted images.

Epidermoid cysts in general are congenital inclusion cystic lesions with intralesional epithelial components.

Intracranial epidermoids account for around 1% of all intracranial tumors and around 3-4% of these arise from the pineal region.

Logical differential diagnoses in this case may include a pineal region arachnoid or dermoid cyst. The former would however not demonstrate any restricted diffusion on DWI, while dermoid cysts will demonstrate some T1 shortening, owing this to intralesional lipid content.

Generally, epidermoid cysts are far more common than dermoid cysts, with a slow growth rate and an eventual large size. They usually present in the third decade of life. Malignant transformation is rare, but if present, histology will usually reveal squamous cell carcinoma.

They are usually plastic lesions with high manoeuvrability, encasing adjacent structures, deeming it difficult for complete resection.

On MRI, They usually appear isointense to CSF on T1 and T2 with incomplete suppression on FLAIR and mixed diffusion restriction and T2 shine-through on the diffusion weighted study. Minimal rim enhancement may be seen on the contrasted study, likely indicating perilesional inflammatory changes. Internal enhancement may indicate malignant transformation.

On CT, they demonstrate almost identical attenuation to the surrounding CSF. Peripheral calcifications may be present.