Intraosseous Myofibroma of the Mandible in a Pediatric Patient: Comprehensive Cone Beam Computed Tomography (CBCT) and Immunohistochemical Characterization.

Intraosseous myofibroma of the mandible is a benign myofibroblastic neoplasm with limited documentation in the pediatric population. This case report outlines the presentation of a nine-year-old girl with a history of swelling and pain involving the lower left side of the face for two months. Examination revealed a mass originating from the posterior part of the mandible, and radiographic evaluation with panoramic radiography and cone beam computed tomography (CBCT) revealed a well-defined unilocular radiolucency with three-dimensional cortical expansion. Pathological examination revealed the hallmark biphasic pattern of myofibroma, characterized by peripheral zones of spindle-shaped myofibroblastic cells arranged in short fascicles and central areas of immature round to oval cells with a hemangiopericytoma-like vascular pattern. Immunohistochemical analysis demonstrated diffuse strong positivity for vimentin and α-SMA, weak positivity for desmin, and negative for S-100 protein, confirming myofibroblastic lineage (the vimentin-actin-desmin cytoskeletal phenotype of myofibroblast) while systematically excluding nerve sheath tumors such as neurofibroma and muscle tumors such as leiomyoma. Conservative surgical excision was performed with preservation of adjacent developing dentition, and the patient is under active follow-up. This case underscores the critical role of histopathological and immunohistochemical evaluation in the definitive diagnosis of intraosseous myofibroma, particularly in differentiating it from a broad spectrum of morphologically similar intraosseous lesions in the growing mandible.