MySpondylitisTeam

Great question — this is a nuanced area that even specialists debate. On MRI, T2 hyperintensity reflects fluid or edema in the sacroiliac joints. The distinction matters a lot for diagnosis.

Active (definite) sacroiliitis typically requires
- Bone marrow edema (BME) seen on STIR or T2 fat-suppressed sequences
- The signal Show Full Answer

Great question — this is a nuanced area that even specialists debate. On MRI, T2 hyperintensity reflects fluid or edema in the sacroiliac joints. The distinction matters a lot for diagnosis.

Active (definite) sacroiliitis typically requires:
- Bone marrow edema (BME) seen on STIR or T2 fat-suppressed sequences
- The signal must be in a subchondral or periarticular location
- Usually needs to be present in at least 2 consecutive slices, or highly intense on 1 slice

"Likely" sacroiliitis is used when:
- T2 hyperintensity is present but doesn't fully meet the above criteria
- There is NO corresponding T1 hypointensity (structural damage like erosion or sclerosis)
- The findings are suggestive but not conclusive Without T1 hypointensity, there's no structural damage confirmed, meaning the inflammation hasn't yet caused bone changes visible on T1. This can make diagnosis tricky because similar signals can come from normal aging or wear and tear — not just spondyloarthritis.

For a formal SpA diagnosis, imaging findings are combined with clinical symptoms, blood markers (like HLA-B27), and history. A rheumatologist experienced in SpA imaging is really important here, as MRI interpretation in this context is highly specialized.

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