- Concentric layers of keratin, crystalline cholesterol, water, and debris from progressive cyst wall desquamation
- Derived from ectoderm but no dermal derivatives (no sebaceous glands, no hair) (as opposed to dermoid cysts)
- MC location: CP angle (basal cistern overally is the most common site)
- Symptoms: headache or other signs of increased ICP, seizure
- Although not common, there is risk of malignant degeneration into squamous cell tumour.
- CT: lobulated mass hypointense to CSF (due to lipid content)
– T1-weighted: normally isointense/mildly hyperintense to CSF
**Rarer forms: White epidermoid — hyperintense to CSF due to lipid content
– T2-weighted: Isointense to mildly hyperintense to CSF
– FLAIR: Incomplete suppression of cyst contents
– DWI: Restricted diffusion, occurring as a result of layered keratin within the cyst
– T1 C+: contents are typically nonenhancing.
– Enhancing mural nodule should raise suspicion for malignant degeneration.