LAUSR

Benign fibrous histiocytomas of soft tissue are composed of spindled fibroblasts arranged in a storiform pattern admixed with secondary elements including histiocytes, foam cells, and inflammatory cells. These tumors occur equally in males and females and most often arise in the dermis and subcutaneous tissues. Benign fibrous histiocytomas of bone comprise approximately 1% of all benign bone tumors. When they do occur in bone they most often affect the long bones with the femur and tibia being preferred sites. Other sites include the pelvic bones, particularly the ilium. Benign fibrous histiocytoma of the jawbones is an exceedingly rare tumor. As of 2016 there have been only 13 cases reported of this unusual tumor arising in the jawbones. We report two new cases of this tumor arising in the mandible, describe its histologic features and immunohistochemical characteristics, and review the literature. Both of our cases presented in young males as expansile lesions of the mandible with associated well defined radiolucencies and perforation of the cortical plates. Both tumors demonstrated spindle cells arranged in a storiform pattern. Case 1 had a more collagenized stroma and demonstrated an abundance of secondary elements while Case 2 exhibited a myxoid background, prominent perivascular hyalinization and scattered secondary elements. Immunohistochemical studies revealed Factor XIIIa and CD68 positivity in both tumors. Case 2 also demonstrated positivity for CD10. S100 and SMA were negative in both lesions. The recognition of the appropriate histologic and immunologic features of this common soft tissue tumor will aid in its diagnosis in an uncommon location.