Diagnostic utility of T1-weighted MRI characteristics in evaluation of osteomyelitis of the foot.

OBJECTIVE: The purpose of this study was to evaluate the diagnostic utility of specific characteristics on T1-weighted MR images in the diagnosis of pedal osteomyelitis.

MATERIALS AND METHODS: The study included all adult patients who underwent MRI of the foot for evaluation of suspected osteomyelitis over an 11-month period. Images were retrospectively reviewed for specific criteria on T1-weighted images, including signal intensity of affected bone marrow (normal or decreased), distribution of abnormal signal intensity (subcortical or medullary), and pattern of involvement (hazy reticulated or confluent). The presence of osteomyelitis was presumed if the surgical pathologic result was positive or if there was lack of clinical improvement despite conservative management. Rapid clinical improvement with conservative management was considered an indication that osteomyelitis was not present.

RESULTS: Images from 74 examinations were evaluated. In 20 cases, osteomyelitis was considered present, and in 54 it was presumed absent. In 19 of the 20 cases (95%) in which osteomyelitis was considered present, marrow T1 signal intensity was decreased, in a medullary distribution, and in a confluent pattern in all cases. In 30 of the 54 cases (56%) in which osteomyelitis was presumed absent, T1 signal intensity was decreased, but only five cases (9%) had a medullary distribution and confluent pattern. Twenty-three cases (43%) had a hazy reticulated pattern, and two cases (4%) had only subcortical distribution. None of the cases with a subcortical distribution or hazy reticulated pattern of abnormal signal intensity had positive results for osteomyelitis. Confluent decreased T1 marrow signal intensity in a medullary distribution was 95% sensitive in the prediction of osteomyelitis with a specificity of 91%, negative predictive value of 98%, and positive predictive value of 79%.

CONCLUSION: Findings on T1-weighted MR images, specifically a confluent pattern of decreased T1 marrow signal intensity in a medullary distribution, correlate highly with the presence of pedal osteomyelitis.