[Aneurysmal bone cyst: diagnostic role of computerized tomography and magnetic resonance]

Aneurysmal bone cysts (ABC) are relatively uncommon benign expansile osteolytic lesions characterized by multiple cavities with serum-blood levels and delimited by a thin periosteal external border. The differential diagnosis is difficult to make with conventional radiography, while CT and MRI are elective techniques. Ten patients with ABC (7 central and 3 eccentric lesions) were examined with CT and MRI. Four cysts were localized at the proximal femur, 2 in calcaneal, 2 in vertebral (cervical and dorsal), 1 in tibial and 1 in iliac sites. Diagnostic criteria were the presence of fluid-fluid levels and a thin hyperdense peripheral border at CT, while hyperintense cavities on T2-weighted sequences, fluid-fluid levels, pseudodiverticular features and a low-signal border were found at MRI. Intralesional levels were detected in 9 patients at CT and in 10 at MRI; the 3 peripheral cysts exhibited a hyperdense extraosseous border at CT, corresponding to the periosteal shell, considered a benignity sign. To conclude, CT and MRI, thanks to their high resolution, clearly depict the anatomopathologic features of ABC, thus allowing this type of lesion to be differentiated from other benign and malignant osteolytic lesions.