skip to main content

Fat Metaplasia SIJ MRI — SCE Rheumatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateMusculoskeletal ImagingFat Metaplasia SIJ MRISCE Rheumatology

A 55-year-old man with chronic back pain undergoes MRI of the sacroiliac joints because axial spondyloarthritis is suspected. T1-weighted images show several well-demarcated subchondral fat lesions in a distribution typical of sacroiliitis. There is no corresponding bone marrow oedema on STIR images. Which interpretation is most accurate?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — They are structural or post-inflammatory lesions that can support axial SpA when typical, but do not demonstrate current active osteitis

Fat metaplasia appears as well-demarcated high T1 marrow signal and is classified as a structural rather than active inflammatory SIJ lesion. In axial SpA it may develop during repair after inflammation and, when sufficiently extensive and distributed typically, supports the diagnosis. However, fat lesions are not specific in isolation and must be correlated with other structural abnormalities and the clinical phenotype. Absence of STIR bone marrow oedema means that this scan does not demonstrate current active osteitis, excluding B. Infection usually produces marked oedema, erosive destruction and soft-tissue inflammation, not isolated typical fat lesions, excluding C. Fat deposition may occur with ageing or degeneration, but cannot invariably be dismissed, excluding D. No isolated MRI lesion independently establishes axial SpA, excluding E.

Reference: Maksymowych WP et al. MRI lesions in the sacroiliac joints of patients with spondyloarthritis: an update of definitions and validation by the ASAS MRI working group. Ann Rheum Dis. 2019;78:1550–1558. https://pubmed.ncbi.nlm.nih.gov/31422357/