A few case series suggest that bone scan has a lower sensitivity in the detection of source of infection relative to MRI [39-41]. MRI Lower Extremity MRI, given its sensitivity to soft-tissue and bone marrow pathology, has high accuracy in diagnosing infection, including septic arthritis, osteomyelitis, pyomyositis, and discitis [42,43], and could be considered as the initial imaging study [44]. Large field-of-view coronal T1-weighted and fluid-sensitive sequences covering from the pelvis and hips to the ankles may be performed to identify any abnormality. Inclusion of the lower thoracic spine and lumbar spine should be considered if lower extremity or hip pathology is not found and symptoms persist, as some patients with discitis may not have localized symptoms to the back [45-48]. Once localized, additional MRI sequences with smaller fields of view can be performed for further characterization [49]. Contrast administration in the MRI evaluation of suspected soft-tissue or osseous infection does not increase sensitivity or specificity but may increase reader confidence and better delineate abscesses [50,51]. Contrast administration during MRI should be considered in specific cases to improve detection of an abscess when there is significant soft-tissue edema [50,51]. An exception to this may be infants, in whom infection of the epiphyses can be occult on unenhanced MRI sequences [52]. Given these considerations, the use of IV contrast may vary with institutional protocol. While no prospective study of MRI versus bone scan has been performed, there are retrospective studies suggesting superiority of MRI over bone scan in detecting the source of infection, with sensitivity of 99% to 100% for MRI compared to 53% to 71% for bone scan [39,40]. Because of low bone scan sensitivity for soft- tissue pathology, MRI is often obtained after a positive bone scan for further evaluation of soft-tissues, primarily to detect abscess formation that requires drainage [41].
Acutely Limping Child Up To Age 5 PCAs. A few case series suggest that bone scan has a lower sensitivity in the detection of source of infection relative to MRI [39-41]. MRI Lower Extremity MRI, given its sensitivity to soft-tissue and bone marrow pathology, has high accuracy in diagnosing infection, including septic arthritis, osteomyelitis, pyomyositis, and discitis [42,43], and could be considered as the initial imaging study [44]. Large field-of-view coronal T1-weighted and fluid-sensitive sequences covering from the pelvis and hips to the ankles may be performed to identify any abnormality. Inclusion of the lower thoracic spine and lumbar spine should be considered if lower extremity or hip pathology is not found and symptoms persist, as some patients with discitis may not have localized symptoms to the back [45-48]. Once localized, additional MRI sequences with smaller fields of view can be performed for further characterization [49]. Contrast administration in the MRI evaluation of suspected soft-tissue or osseous infection does not increase sensitivity or specificity but may increase reader confidence and better delineate abscesses [50,51]. Contrast administration during MRI should be considered in specific cases to improve detection of an abscess when there is significant soft-tissue edema [50,51]. An exception to this may be infants, in whom infection of the epiphyses can be occult on unenhanced MRI sequences [52]. Given these considerations, the use of IV contrast may vary with institutional protocol. While no prospective study of MRI versus bone scan has been performed, there are retrospective studies suggesting superiority of MRI over bone scan in detecting the source of infection, with sensitivity of 99% to 100% for MRI compared to 53% to 71% for bone scan [39,40]. Because of low bone scan sensitivity for soft- tissue pathology, MRI is often obtained after a positive bone scan for further evaluation of soft-tissues, primarily to detect abscess formation that requires drainage [41].