Adamantinoma. A case report with aspiration cytology and differential diagnostic and immunohistochemical considerations.

Fine needle aspiration biopsy of bone lesions is routinely used in the metastatic workup of patients with radiographically suspicious areas. However, caution must be used when interpreting smears from aspirates performed on primary bone neoplasms. These tumors are often heterogeneous, and problems with sampling may be encountered. We report a case of a 25-year-old male who presented with a 3-cm lytic lesion in the tibia. A diagnosis of benign fibroosseous lesion was based on the clinical presentation, radiographic appearance and presence of numerous sheets and single cytologically bland spindle cells. Subsequent curettage of the specimen revealed an adamantinoma with a prominent fibrous component. Most of these rare, locally aggressive neoplasms are located in the tibia. They are characterized histologically as having a fibrous background with islands of basaloid, spindle or squamoid cells. Furthermore, a differentiated, regressing variant with an osteofibrous dysplasia-like appearance also exists. Smears consisting primarily of spindle cells or fibrous tissue may lead to an erroneous diagnosis of a fibrohistiocytic neoplasm, fibrous dysplasia, fibrous cortical defect or ossifying fibroma. Pertinent cytomorphologic features should aid in establishing the correct diagnosis of adamantinoma.