Differential diagnosis between osteomyelitis and bone tumors

Background: Hematogenous osteomyelitis is often difficult to distinguish from a bone tumor because clinical findings are noncontributory and radiological features can mimic a bone tumor. Recently, the penumbra sign, a higher signal intensity feature of the thin layer of granulation tissue which lines the abscess cavity on T1-weighted magnetic resonance (MR) images, has been reported to be helpful for discriminating subacute osteomyelitis. Purpose: To determine helpful findings for distinguishing osteomyelitis from bone tumors. Material and Methods: The laboratory and imaging findings of a consecutive series of 244 patients referred to our institution with a suspected bone tumor were reviewed. There were 15 cases of osteomyelitis, 160 bone tumors, and 69 tumor-like lesions. Results: In osteomyelitis, the C-reactive protein (CRP) level increased in nine patients and the penumbra sign was seen in 11 patients. In bone tumors and tumor-like lesions, a high CRP level was observed in 21 patients and the penumbra sign was seen in two patients. The sensitivity of the penumbra sign for osteomyelitis was 73.3%, with a specificity of 99.1%. Conclusion: The penumbra sign and a high CRP level support the diagnosis of osteomyelitis and may help to exclude the presence of a tumor.