[Low grade intramedullary osteosarcoma. Apropos of 8 cases]

The authors reviewed eight patients treated for Low Grade Intramedullary Osteosarcoma (LGIO). They analyzed the radiographical and histological features and evaluated the prognosis of this disease.

Eight cases of LGIO were studied. The mean follow-up period was 3.9 years. LGIO is defined as a Broders classification grade I osteosarcoma. The study involved 3 males and 5 females. Mean age at the time of diagnosis was 28.

Clinical records, radiographs and C.T. Scan were available and reviewed in all cases. Five patients had had MRI. In addition to the conventional histological study, ultrastructural studies were conducted in three of the cases. On their last examination, all patients received a clinical and X-ray assessment.

The tumor was localized around the knee in six cases on the humerus and on the proximal femur in one case. The tumor was situated in the metaphysis and was most often lytic. A malignant tumor was suspected at the outset for only two of the patients. The scanner and the MRI revealed a cortical discontinuity and extraosseous involvement in five cases. Seven patients had a wide resection, which was intra-tumoral once. The histological examination of two of those resections revealed limited areas of anaplasia; complementary chemotherapy was then conducted. We did not observe any local recurrence in this group. We observed, however, an iliac metastasis, for which another wide resection was performed. This last patient remained free of disease three years later. One patient had radiotherapy and chemotherapy; he died from pulmonary metastasis after his LGIO turned into high grade osteosarcoma.

LGIO are rare, they represent 1.8 per cent of all Osteosarcomas in the Cochin file. The mean age of patients contracting LGIO is higher than that of conventional osteosarcoma patients. Observation of the radiographs and histological examination could lead to think the tumor is benign, and mistake it with a fibrous displasia. The C.T. Scan and the MRI have the advantage of showing soft tissue invasion and help the histological examination. The wide resection is the only treatment able to cure the patient. Chemotherapy would be useful for LGIO cases containing limited arcas of anaplasia.

LGIO is a slowly-evolving tumor. It remains localized for a long period of time. The histological diagnosis is difficult and requires a pathologist familiar with bone tumors. Its treatment requires surgery. LGIO must be distinguished from conventional osteosarcomas because of its better prognosis.