BONE ISLAND - SCINTIGRAPHIC FINDINGS AND THEIR CLINICAL-APPLICATION

PURPOSE: TO evaluate bone islands that showed increased uptake of radi otracer on skeletal scintigraphy and to present an algorithm for exami ning such lesions to avoid misdiagnosis in difficult cases. PATIENTS A ND METHODS: Over an 8-year period, 20 patients (10 men and 10 women ra nging in age from 33 to 82 years) with bone islands that showed activi ty on skeletal scintigraphy were examined with plain radiography (all patients), computed tomography (CT; 5 patients) and magnetic resonance imaging (MRI; 4 patients). For six of the patients the clinical prese ntation and the radiologic studies suggested malignancy, which prompte d biopsy and histopathologic examination. Histopathologic study was al so performed for six other patients in whom the bone islands were foun d incidentally during evaluation for joint replacement surgery for ost eoarthritis. in the last eight patients the lesions exhibited the char acteristic radiologic features of enostosis, and these patients were f ollowed for up to 3 years without biopsy. RESULTS: In all cases plain radiography showed the characteristic features of a bone island: a hom ogeneously dense, sclerotic focus in the cancellous bone with distinct ive radiating bony streaks (''thorny radiation'') that blended with th e trabeculae of the host bone to create a feathered or brush-like bord er. Histopathologic examination of scintigraphically active bone islan ds showed increased osteoblastic activity, and the lesions were marked by a mixture of compact and trabecular bone. In the patients who did not undergo biopsy but were followed with radiologic examinations, the re was no change in the size or appearance of the lesions. CONCLUSIONS : The key to the correct diagnosis of bone island Lies in the distinct ive radiographic features of enostosis. An asymptomatic, isolated scle rotic bone lesion showing feathered or brush borders is most Likely an enostosis, regardless of its size or its activity on scintigraphy. Th erefore, a practical algorithm for examining bone islands should now f rom their morphologic features as observed on radiographs and CT and M RI scans, rather than from their activity on scintigraphy.