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Introduction: Aneurysmal bone cyst (ABC) is a benign but locally aggressive bone lesion that sometimes occurs in soft tissues. In bones, it forms an expansile, multiloculated, lytic lesion containing blood-filled cystic spaces (as seen in this low power scan). It was initially thought to be a reactive process as it shares features with giant cell reparative granuloma, heterotopic ossification, and response to trauma/fracture. However, the discovery of USP6 gene rearrangements caused by balanced chromosomal translocation t(16;17)(q22;p13) in about 75% of cases has confirmed the neoplastic nature of ABC.
ABC can occur de novo (primary ABC; 70% of all cases) or ABC-like changes (secondary ABC; a term no longer recommended) may be 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. ABC-like changes don't show USP6 gene rearrangements. Rare examples of ABC are solid (so-called solid variant) and lack blood-filled cystic spaces or fibrous septa.
ABC can occur de novo (primary ABC; 70% of all cases) or ABC-like changes (secondary ABC; a term no longer recommended) may be 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. ABC-like changes don't show USP6 gene rearrangements. Rare examples of ABC are solid (so-called solid variant) and lack blood-filled cystic spaces or fibrous septa.