Squamous cell carcinoma arising from an epidermoid cyst of the buttock: Imaging findings and case report

We report a rare case of squamous cell carcinoma (SCC) arising from a subcutaneous epidermoid cyst in the buttock of an 80-year-old man who presented with a painful mass. MRI revealed a well-defined subcutaneous mass, measuring approximately 10 cm, in the medial aspect of the left buttock, which exhibited internal features typical of an epidermoid cyst. However, MRI also demonstrated a significant finding: a 45-mm solid mural component protruding into the cyst. This solid component exhibited mild high signal intensity on T2-weighted images and heterogeneous signal intensity on DWI, differing from the cystic portion. Color Doppler ultrasound demonstrated internal blood flow within this solid component. Crucially, this solid component was absent on a CT scan performed 2 years prior. Resection and subsequent pathological examination confirmed well-differentiated squamous cell carcinoma (SCC) arising from the epidermoid cyst. This case highlights the importance of considering malignant transformation in epidermoid cysts, especially when imaging findings such as interval development of a solid mural component and internal vascularity are observed.