Radiological and Histological Findings of Primary Pleomorphic Rhabdomyosarcoma Arising from the Mandibular Gingiva: A Case Report and Literature Review

Background: Pleomorphic rhabdomyosarcoma (RMS) is a rare, adult-predominant high-grade sarcoma that usually arises in the deep soft tissues of the extremities. Primary oral pleomorphic RMS is exceptionally rare, and detailed CT and MRI characteristics of oral pleomorphic RMS remain sparsely documented. Case Presentation: A 66-year-old woman presented with a two-month history of lower anterior tooth pain and progressive mandibular swelling, initially misdiagnosed and treated as a dental infection. CT and MRI revealed a 3.8-cm heterogeneously enhancing mass centered in the mandibular gingiva, with aggressive cortical destruction, diffusion restriction, and anterior floor-of-mouth extension; oral cavity cancer (squamous cell carcinoma) was initially favored on imaging. The patient underwent wide excision with segmental mandibulectomy and fibular osteocutaneous free-flap reconstruction. Histopathologic examination confirmed a high-grade pleomorphic RMS with immunoreactivity for desmin and MyoD1. The patient received adjuvant chemotherapy and radiotherapy, with no recurrence at 8-month follow-up. Conclusions: Pleomorphic RMS of mandibular gingiva may be mistaken clinically for odontogenic infection and radiologically for squamous cell carcinoma. Although imaging findings are nonspecific, CT and MRI are essential for defining mandibular and floor-of-mouth involvement and planning resection; definitive diagnosis requires histopathologic and immunohistochemical confirmation.