Epidermoid

Epidermoid is a descriptive term used in medical pathology to denote lesions that resemble epidermal tissue in their lining or structure. The term is most often encountered in reference to epidermoid cysts and intracranial epidermoid tumors, and historically in reference to epidermoid carcinoma, an older term for malignant squamous cell carcinoma.

Epidermoid cysts, also called epidermal inclusion cysts, are benign, slow-growing lesions of the skin. They are typically lined by stratified squamous epithelium with a granular layer and filled with laminated keratin. These cysts usually arise in the dermis or subcutaneous tissue and commonly occur on the face, scalp, neck, or trunk. Clinically they present as a small, firm, mobile bump, sometimes with a central punctum. Treatment is usually surgical excision with removal of the cyst wall; recurrence is uncommon when the wall is completely removed.

Intracranial epidermoid tumors are benign congenital cysts that originate from ectodermal cells trapped during neural development. They most often locate in the cerebellopontine angle or parasellar region and grow slowly, potentially causing symptoms from mass effect or cranial nerve compression. On MRI, they commonly follow CSF signal on T1- and T2-weighted sequences but can show characteristic diffusion restriction due to the keratin content, aiding distinction from other cystic lesions. Management is surgical removal, with the goal of complete excision to minimize recurrence.

Epidermoid carcinoma is an older term for malignant squamous cell carcinoma arising in various sites such as skin, lung, head and neck, or esophagus. It reflects histologic resemblance to epidermal squamous epithelium rather than true epidermal origin. Treatment and prognosis depend on the tumor’s location, stage, and patient factors.