In suspected osteomyelitis, which imaging modality is most sensitive in early disease?

• A. X-ray
• B. MRI
• C. CT scan
• D. Ultrasound

Answer: (B)

The key point is recognizing how early osteomyelitis affects bone tissue and how different tests pick up those changes. In the very early stage, infection is centered in the bone marrow, causing edema before any visible cortical bone destruction. MRI is able to detect this bone marrow edema and inflammatory changes right away, making it the most sensitive test for early disease.

X-ray often appears normal in the first days to weeks because bone changes lag behind the inflammation. CT excels at detailing cortical bone and detecting bony destruction or sequestra but isn’t as good at picking up early marrow changes. Ultrasound can reveal soft tissue involvement or abscesses but doesn’t visualize bone marrow well, so it’s not the best for early detection of osteomyelitis.

On MRI you’d expect to see bone marrow edema with low signal on T1 and high signal on T2/STIR, with enhancement after contrast indicating infection. Diffusion-weighted imaging can also help differentiate infected tissue. Thus, MRI’s ability to visualize early marrow involvement makes it the preferred modality for early osteomyelitis.