title: Bone-within-bone appearance: a red flag for biphosphonate-associated osteonecrosis of the jaw.
abstract: 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.
authors.affiliation: Section Neuroradiology, NYU Langone Medical Center, New York, NY 10128, USA. giriman@hotmail.com
authors.forename: Girish M
authors.initials: GM
authors.lastname: Fatterpekar
authors.forename: Julius Valentin
authors.initials: JV
authors.lastname: Emmrich
authors.forename: Jean Anderson
authors.initials: JA
authors.lastname: Eloy
authors.forename: Amit
authors.initials: A
authors.lastname: Aggarwal
mesh_terms: D000368:Aged; D001706:Biopsy; D050071:Bone Density Conservation Agents / Q000009:adverse effects*; D003937:Diagnosis, Differential; D004164:Diphosphonates / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007571:Jaw Diseases / Q000139:chemically induced* / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D010019:Osteomyelitis / Q000000981:diagnostic imaging; D010020:Osteonecrosis / Q000139:chemically induced* / Q000000981:diagnostic imaging*; D010025:Osteoradionecrosis / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D050071:Bone Density Conservation Agents; D004164:Diphosphonates