Pilomatrixoma of the medial arm presenting as an indeterminate soft tissue lesion on MRI: A case report

Pilomatrixoma is a benign hair follicle matrix cell tumor and one of the most common cutaneous tumors in children and young adults. We present the case of a 33-year-old male evaluated for a progressively enlarging, pruritic subcutaneous nodule on the medial right arm. Multimodal imaging, including ultrasonography and magnetic resonance imaging (MRI), revealed an indeterminate, hypervascular dermal mass measuring 8 × 17 × 11 mm with hypodermal extension. Given the ambiguous radiological features and increasing functional discomfort, the patient underwent an elective excisional biopsy under local anesthesia approximately five months after the initial ultrasound. Histopathological analysis established the definitive diagnosis of a 1.7 cm pilomatrixoma characterized by focal induration and microcalcifications. The postoperative course was uneventful. This case highlights the diagnostic limitations of cross-sectional imaging for atypical superficial soft-tissue masses and reinforces the necessity of surgical excision for definitive histopathological characterization.