Nodular fasciitis of the masseter muscle: Radiologic and pathologic correlation of a rare benign lesion

Nodular fasciitis rarely arises from the masseter muscle and is frequently misdiagnosed as soft tissue sarcoma. A 43-year-old male presented with a rapidly enlarging, painless swelling below the right mandibular angle over 2 months. Clinical examination revealed a firm, mobile mass without skin fixation or lymphadenopathy. Ultrasound and magnetic resonance imaging were performed, followed by fine-needle aspiration cytology and excisional biopsy. Ultrasound demonstrated a well-defined, hypoechoic lobulated lesion (23 × 13 × 8 mm) within the superficial masseter, showing mild internal vascularity and no bone involvement. Magnetic resonance imaging revealed an iso- to slightly hypointense T1 signal, hyperintense T2/ short tau inversion recovery signal, and homogeneous postcontrast enhancement with smooth margins, features suggestive of a benign myofibroblastic lesion. Excisional biopsy confirmed the diagnosis of nodular fasciitis. This case indicates that masseteric nodular fasciitis, a rare benign lesion, may present with imaging features of small size, smooth margins, homogeneous enhancement, and mild vascularity in the context of trauma history. Recognition of this self-limited myofibroblastic proliferation can prevent unnecessary radical surgery and guide conservative management.