Inflammatory myofibroblastic tumor of the tetromolar trigons

Inflammatory myofibroblastic tumor (IMT) of the oral cavity is an extremely rare clinical and pathological disease entity. It was originally described in the lung but has recently been reported in a variety of locations including lungs, mesentery, omentum, retroperitoneum and other sites. IMT is an unusual tumor composed of differentiated myofibroblastic spindle cells usually accompanied by numerous plasma cells and lymphocytes. We report such a case of inflammatory myofibroblastic tumor of the retromolar trigon in a 11-year-old girl. The patient presented with a soft tissue mass in the retromolar trigon. Histologically, the lesion is dominated by differentiated spindle cells with aprominent collagenous stroma and an inflammatory component including plasma cells and lymphocytes, and with positive immunoreactivity for smooth muscle actin (SMA) and vimentin. The absence of cytologic atypia helps differentiate this lesion from malignant spindle cell tumors.