Proliferative trichilemmal cyst of the plantar surface: An unusual localization: A case report

Trichilemmal cysts, also known as pilar cysts, are benign dermal epithelial tumors arising from the hair follicle, most commonly located on the scalp. Localization on the plantar surface is extremely rare. We report the case of a 27-year-old male presenting with a firm, mobile mass on the lateral plantar surface of the left foot, causing hyperkeratosis and functional discomfort while walking, without limitation in daily activities. The lesion had progressively enlarged over two years. Ultrasound revealed a subcutaneous, heterogeneous, isoechoic mass with ill-defined margins and marked peripheral Doppler vascularization. MRI showed a homogeneous, T1-isointense lesion without diffusion restriction and mild peripheral gadolinium enhancement. Surgical excision revealed a well-demarcated, reddish, friable mass. Histopathological analysis demonstrated a cystic structure lined by stratified squamous epithelium without a granular layer. The cyst contained compact, trichilemmal-type keratin with central calcification. The pericystic stroma consisted of fine fibrous tissue, and a superficial peripheral venous network was noted. No atypia or malignancy was observed. This case highlights the unusual plantar localization of trichilemmal cysts and underscores the importance of histological examination for definitive diagnosis, particularly in lesions with atypical clinical or radiological features.