Presentation
Recent blow to left parietal region. CT scan to assess for intracranial injury. No previous history of malignancy.
Patient Data
Small left parietal scalp hematoma (arrow) with adjacent expansile soft tissue mass in the skull vault. Soft tissue density not fat so not a dermoid. Bone margins are regular or scalloped. Incidental right skull vault osteoma.
Mass shows restricted diffusion (confirmed on the ADC map indicative of epidermoid).
Case Discussion
A benign, slow-growing lesion of the skull due to aberrant epidermal inclusion in the calvaria. Differential diagnosis is Langerhans cell histiocytosis in a child/young adult, metastasis and plasmacytoma. Key to diagnosis is the intradiploic location with well-demarcated lysis expanding both the inner and outer tables of the skull and well defined borders. The MRI findings of marked restricted diffusion are typical of epidermoid.