Giant Plantar Epidermoid Cyst with Invasion of the Interosseous Muscles.

Epidermoid cysts of the sole of the foot are rare lesions that must be differentiated from other, more common subcutaneous pathologic abnormalities located on the sole. Cases of epidermoid cysts that extend to the interosseous musculature are rarer still. We report the case of a giant epidermal cyst in a 64-year-old individual that extended to the intrinsic musculature of the third space of the right foot and that was diagnosed after fine-needle aspiration biopsy and subsequent cytologic study. Differential diagnosis of these lesions should be made with the support of additional imaging tests, and diagnostic confirmation should always be obtained after surgical removal and subsequent histopathologic study.