OSTEOSARCOMA - LOW-GRADE INTRAOSSEOUS-TYPE OSTEOSARCOMA, HISTOLOGICALLY RESEMBLING PAROSTEAL OSTEOSARCOMA, FIBROUS DYSPLASIA, AND DESMOPLASTIC FIBROMA

Background. Low-grade intraosseous osteosarcoma is a rare variety of osteosarcoma and it is difficult to recognize. Methods. A series of 10 patients with low-grade intraosseous osteosarcoma is reported. These patients were identified from the Istituto Rizzoli files, which includes approximately 1000 cases of osteosarcoma. Clinical data and radiographic and histologic features were studied. Results. The radiographic appearance confirmed malignancy in five patients and suggested it in two. A benign lesion was diagnosed in three patients. Three lesions resembled parosteal osteosarcoma, two appeared similar to fibrous dysplasia, and two had features of desmoplastic fibroma. A mixed histologic pattern was found in three other tumors. Recurrence after intralesional excision in all patients indicated the aggressive nature of this lesion. The development of metastases in two patients and progression in the grade of malignancy in one of these highlighted the malignant nature of the tumor. Conclusions. The correct diagnosis would permit adequate treatment with wide surgical margins.