Unexpected trichilemmal cyst of the thigh: MRI appearance at an atypical site

Abstract

Trichilemmal (pilar) cysts are benign lesions that originate from the outer root sheath of hair follicles and most commonly occur on the scalp. However, they can occasionally present in atypical locations. We describe the case of a 36-year-old woman who presented with a slowly enlarging, superficial right-thigh mass that was mobile and mildly tender on examination. Magnetic resonance imaging (MRI) demonstrated a well-circumscribed, round lesion with T1/T2 hypointensity and internal foci of low signal, suggestive of a benign lesion, such as a trichilemmal cyst. Surgical excision was performed, and histopathology confirmed the diagnosis. Recognizing the imaging characteristics of trichilemmal cysts is important for distinguishing them from other soft tissue lesions, including pilomatrixomas, epidermoid cysts, and lipomas.