Quantitative analysis of the plain radiographic appearance of unicameral bone cysts

RATIONALE AND OBJECTIVES. The authors determine the features that distingui sh the radiographic appearance of unicameral bone cysts (UBC) from other so litary lesions of bone and to develop an ordered differential of similar-ap pearing lesions. MATERIALS AND METHODS. Seven hundred nine cases of solitary bone lesions, i ncluding 40 UBCs, were analyzed according to demographic, anatomic, and pla in radiographic features. Vector analysis of both classic and new groups of features was performed to determine the sensitivity and specificity of rad iographs for UBC and an ordered differential based on radiographic features . RESULTS. The features of the UBCs in this study compared favorably with tho se in the literature. The male:female ratio was 3.3:1, with an average age of 15 +/- 13 years. Age ranges and lesion diameters were similar for both s exes. Thirty-three of the 40 (83%) UBCs were in long bones, and seven were in the pelvis or calcaneus. All 40 UBCs were geographic, medullary, and lyt ic. None had an associated soft-tissue mass. Fifty-five percent had patholo gic fractures, and 10% had fallen fragment signs. Ninety-eight percent had no cortical break, and 88% had well-defined margins. CONCLUSION. Classic descriptions of UBCs can be refined to improve sensitiv ity without sacrificing specificity. The best vector in this study had a se nsitivity of 80% and a specificity of 93% and included these radiographic f eatures: metaphyseal, diaphyseal, or flat bone location, geographic, lytic, medullary-based, no matrix, no satellite lesions, no subarticular extensio n, no soft-tissue mass, no cortical break, and central location in long bon es. An ordered differential diagnosis, starting with the most likely lesion , includes enchon-droma, aneurysmal bone cyst, fibrous dysplasia, nonossify ing fibroma, Brodie abscess, and chondrosarcoma.