Aneurysmal Bone Cyst : Case 4

Comments:
Secondary Aneurysmal Bone Cyst (ABC): About 70% of ABCs arise de novo (primary ABC). The remainder consist of ABC-like changes (secondary ABC; a term no longer recommended) seen in association with many benign bone tumors such as chondroblastoma, giant cell tumor, osteoblastoma, fibrous dysplasia, nonossifying fibroma, chondromyxoid fibroma, and rare cases of malignant tumors such as osteosarcoma.

This MRI (T1 fat sat image) shows an example of ABC-like changes in association with a pathology-proven giant cell tumor (GCT) involving the sacrum in a 15 y/o male. There is an expansile, lobulated mass centered in the right sacral ala effacing the right S1 neuroforamen. The mass has enhancing septations, as well as other areas of nonenhancing T1 hyperintensity consistent with internal hemorrhage. STIR sequence showed these to be multiple cystic areas containing fluid-fluid levels. About 15% of GCT have ABC-like changes.

Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org. From the case rID: 7488