Slide 1: Does this patient with a foot ulcer have osteomyelitis?
Slide 2: Yes! In fact there are multiple signs of osteomyelitis: destruction of the bone and joint, sinus tract leading from the skin to the cortical surface, and ill-defined lucency and erosion of the cortex with adjacent fluffy periosteal reaction.
Slide 3: The same patient has an MRI, which also shows signs of osteomyelitis. Coronal sections are shown: fluid-sensitive T2 sequence and fat-sensitive T1 sequence. In the fluid-sensitive T2 sequence the bone of the 5th digit is edematous and significant edema in the soft tissues which abuts the bone of the 5th digit. In the fat-sensitive T1 sequence, loss of the normal fatty marrow in the bone, as it is replaced by infection and edema.
Slide 4: The radiographic findings of osteomyelitis (OM) evolve over time. At 2 days, MRI can detect the earliest findings of OM: loss of T1 marrow signal in the affected bone and corresponding T2 signal. At 2 weeks, earliest findings on x-ray can be delayed up to 2 weeks: cortical erosion, periosteal reaction, and hyperlucent bone. After 6 weeks, findings of chronic OM start to appear: lucent lesions with surrounding sclerosis on x-ray as well as intraosseous abscess and de-vascularized bone on MRI.
Slide 5: Let’s review some key imaging considerations for suspected osteomyelitis. What is the initial imaging modality of choice? A plain film. X-rays are a cheap and efficient way to screen for other etiologys and complications.
What if the radiographs are inconclusive? Follow up with an MRI. X-ray is often negative in early OM. MRI the most sensitive modality (90% sens., 79% spec.)
Is MRI contrast required? Contrast is not necessarily required. But, contrast will display intraosseous enhancement, which is compatible with OM.
Tags: MRI, musculoskeletal, osteomyelitis, radiology, reading room, x-ray