MRI evaluation of bone marrow changes in the diabetic foot: a practical approach.

One of the most important roles of magnetic resonance (MR) in imaging of the diabetic foot is to differentiate between the common and often comorbid pathologies that present with abnormal bone marrow signal. The primary diagnostic challenges in this setting are to distinguish osteomyelitis from reactive bone marrow edema, neuroarthropathy from osteomyelitis, and the sterile from the superinfected neuropathic joint. Whereas both osteomyelitis and reactive marrow edema share increased T2 signal, osteomyelitis is confirmed by T1 hypointensity in the bone marrow and reactive edema demonstrates isolated T2 signal hyperintensity. In distinguishing osteomyelitis from neuroarthropathy, a localized or contiguously spreading forefoot focus of abnormal bone marrow away from the subchondral surface and adjacent to a skin ulcer, cellulitis, abscess, or sinus tract would be indicative of osteomyelitis. A midfoot, subchondral, periarticular, or polyarticular distribution of findings in the absence of a contiguous focus of skin disruption would strongly support neuroarthropathy. Parameters that have been successfully correlated with acute infection superimposed on neuroarthropathy include diffuse bone marrow signal abnormality, progressive subarticular enhancement, loss of subchondral cysts, and the presence of the MRI "ghost sign."