Intradiploic Epidermoid Cyst :A Mystery in the Mastoid Bone_Case No: NR.1.5.1.2.002
Updated: May 9
Clinical Profile
Patient: 25-year-old female.
Presentation: Slow-growing, painless, firm swelling in the left mastoid region.
Radiological Findings:
1. CT: The Architecture
A well-defined, lytic lesion significantly expanding the outer table of the left mastoid bone. The sclerotic margins indicate a slow-growing, benign process.
2. MRI: Tissue Identity
T1: Hypointense.
T2: Heterog
eneously hyperintense.
Contrast T1: No internal enhancement, but minimal peripheral rim enhancement is visible.
Post-contrast T1 FS Axial Remember: internal enhancement should lead you to consider other diagnoses!
3. DWI: The Identity Card
The lesion glows bright white on DWI (Diffusion Restriction).
DWI: High signal.
ADC: Low signal.
Differential Diagnosis: The Fine Line
It is easy to confuse an epidermoid cyst with arachnoid granulations, hemangiomas, or fibrous dysplasia. However, each has a unique "radiological signature." For instance, why does a hemangioma
behave differently on T1? Or why is a cholesteatoma usually associated with the mastoid antrum?
💡 Academic Pearl: If a bone lesion is lytic on CT, fluid-like on MRI, and shows restricted diffusion on DWI; an Epidermoid Cyst should always be at the top of your list.
📚 Want to Learn More?
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