Epidermoid Cysts in the CNS

Abstract Purpose of review Epidermoid cysts (ECs) are slow-growing, non-neoplastic cysts of the central nervous system that can occur intracranially or in the spinal canal. This review synthesizes the current literature on ECs, with emphasis on etiology, clinical presentation, imaging features, complications, differential diagnosis, and treatment, while contrasting them with related entities such as dermoid cysts, teratomas, arachnoid cysts, and cholesteatomas. Recent findings Contrast-enhanced MRI with diffusion-weighted imaging remains the modality of choice for evaluation, with avid diffusion restriction the pathognomonic feature that differentiates classic ECs from arachnoid cysts and other mimics. Recent literature has further characterized the “white” or “dense” epidermoid variant, which demonstrates hyperdensity on CT, T1 hyperintensity, and variable diffusion characteristics owing to internal cholesterol clefts, microcalcifications, proteinaceous debris, and hemorrhage. Malignant transformation into squamous cell carcinoma, though exceedingly rare, is suggested by new focal enhancement, worsening perilesional edema, and/or emerging satellite lesions. Surgical excision is the mainstay of treatment, with the extent of resection being the strongest determinant of recurrence. Summary ECs are histologically benign lesions with a broad anatomic distribution throughout the CNS, often reaching considerable size before becoming symptomatic from locoregional mass effect. Awareness of both classic imaging features and atypical variants, as well as complications such as rupture, infection, and malignant transformation, is essential for accurate diagnosis and optimal patient care.