Bone-within-bone appearance: a red flag for biphosphonate-associated osteonecrosis of the jaw.

OBJECTIVE: Osteonecrosis of the jaws is recognized as a serious complication of biphosphonate therapy. The purpose of this study was to characterize the computed tomography (CT) imaging appearance of biphosphonate-associated osteonecrosis and to evaluate for distinguishing features of radiation-induced osteonecrosis (RION), osteomyelitis (OM), and metastases.

METHODS: We retrospectively reviewed CT scans of 6 patients with biopsy-proven biphosphonate-associated osteonecrosis (BAON). Computed tomographic scans were evaluated for presence of periosteal reaction, cortical erosion, reactive sclerosis, fragmentation and collapse of the underlying bone, destruction of the underlying trabecular bone manifested as radiolucency, sequestrum, and presence of any underlying bone expansion. Examinations were also assessed for presence of associated soft tissue mass. For comparison, we also retrospectively analyzed the CT scans of 5 patients with biopsy-proven RION of the jaw, 6 patients with OM, and 4 patients with metastases.

RESULTS: An expansile lytic lesion with dense central sequestrum likened to a "bone-within-bone" appearance is highly suggestive of BAON. No RION or OM cases demonstrated an expansile lytic process. Instead, all the RION cases showed fragmentation and collapse of the underlying bone. Presence of cortical erosion, reactive sclerosis, radiolucency, and associated soft tissue mass should raise the possibility of OM in the appropriate clinical setting.

CONCLUSIONS: In an appropriate clinical setting, a bone-within-bone appearance should alert the clinician to the possibility of BAON.