Epidermoid cyst

  • 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.

Radiographic features:

  • CT: lobulated mass hypointense to CSF (due to lipid content)
  • MRI:
    – 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.

Reference: radiopaedia.org


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