Diagnosis is presumptive by radiological criteria (diffusion restriction).

Differentials are Langerhans cell histiocytosis, hemangioma, metastasis or plasmacytoma. 

Key to diagnosis is well-demarcated lytic lesion expanding both the inner and outer tables of the skull with sharply sclerotic margins. The MRI findings of marked restricted diffusion are typical of epidermoid.

Case courtesy of Dr Ayman Al Basmy, Dr Mohamed Hommos & Dr Mohamed Ibrahim