T1-weighted MRI Imaging Features of Pathologically Proven Non-pedal Osteomyelitis

Rationale and Objectives: The objective of our study was to determine if the T1-weighted magnetic resonance imaging (MRI) features associated with diabetic pedal osteomyelitis are present in histopathologically proven cases of non-pedal osteomyelitis. Materials and Methods: Seventy-five patients with a histopathologically proven diagnosis of non-pedal osteomyelitis and a preoperative MRI were identified between 2000 and 2007. The MRIs were retrospectively reviewed for signal characterization of T1-weighted images, including the signal intensity compared with skeletal muscle, distribution of abnormal signal intensity, and pattern of abnormal signal intensity. A subsequent chart review was performed to identify potential clinical factors that were more associated with atypical T1 features of osteomyelitis. Fisher's exact test was performed to determine if there was a statistically significant difference in the T1-weighted imaging features of the hematogenous and nonhematogenous mechanisms of infection. Results: Seventy of 75 cases demonstrated T1-weighted imaging features typical of pedal osteomyelitis with a confluent region of decreased signal intensity, hypointense, or isointense relative to skeletal muscle in a geographic pattern with medullary distribution. Of the 5 cases that did not demonstrate the typical T1 features associated with pedal osteomyelitis, 4 were considered to have a hematologic mechanism of infection given the absence of surgery, skin ulceration, or a penetrating injury. Conclusion: The majority of cases of non-pedal osteomyelitis in our study demonstrate the typical T1-weighted imaging features previously documented to correlate with the diagnosis of pedal osteomyelitis. The cases in our series that did not demonstrate the typical T1-weighted features were predominantly secondary to a hematologic mechanism of infection.