This document provides information on imaging mimics of sacroiliitis. It discusses how conditions like reactive arthritis, enteropathic arthropathy, infections, tumors, and other disorders can appear similar to sacroiliitis on imaging. It provides details on MRI protocols for evaluating the sacroiliac joints and spine. Common MRI findings in spondyloarthritis are described along with differential diagnoses. Guidelines are presented for simple MRI requests to assess for spondyloarthritis.

1. Imaging Mimics of Sacroiliitis
Physician / Mohammad Abdelbaky
M.Sc. Physical Medicine, Rheumatology & Rehabilitation
Ass. Lecturer – Al Azhar University
(Assiute)
Egypt
mohammadbaky@gmail.com

2. J. Scott Bainbridge, MD, www.DenverBackPainSpecialists.com

3. J. Scott Bainbridge, MD, www.DenverBackPainSpecialists.com

5. Normal X-ray

6. CT scan
Maxime DOUGADOS, MD Paris Descartes University

7. Normal MRI
Coronal T1

8. Ultrasonography
Maxime DOUGADOS, MD Paris Descartes University

10. Grade 0 Grade 1
Grade 2
Grade 3
Grade 4

11. 1984 Modified New York Criteria for AS
Clinical Criteria
•Low back pain ≥ 3 months, improved by exercise and not relieved by rest
•Limitation of lumbar spine in sagittal and frontal planes
•Limitation of chest expansion (relative to normal values corrected for age and
sex)
Radiological criteria
•Bilateral grade 2-4 sacroiliitis OR
•Unilateral 3-4 sacroiliitis
Requirements: bilateral grade 2-4 or unilateral grade 3-4 sacroiliitis AND any
clinical criteria (see XRay Grading of SI joints).
Reference: Van der Linden et al. Arthritis Rheum 1984;27:361.

13. MRI

14. MRI Protocol
SIJ Protocol:
According to the ASAS classification criteria, active inflammatory lesions are best visualized on with whole-body of
1.0 or 1.5 Tesla MRI:
Sequences
• STIR or fat-suppressed (fs.) T2.
(512 pixel matrix, 3 – 4 mm slice thickness).
• T1: Structural damage and chronic lesions, such as fatty degeneration and erosions.
• fs. gadolinium-enhanced T1: in cases of doubt and high suspicion.
Orientation
• Semicoronal sections at least 10 – 12 slices.
• - + axial oblique.
van den Berg R, van der Heijde DM. 2010: How should we diagnose spondyloarthritis according to the ASAS classification criteria: a guide for practicing physicians. Pol Arch Med Wewn;
120:452???457
Clarissa Canella, Bruno Schau, Elisio Ribeiro, Bruna Sbaffi and Edson Marchiori 2013: MRI in Seronegative Spondyloarthritis: Imaging Features and Differential Diagnosis in the Spine
and Sacroiliac Joints, American Journal of Roentgenology, Volume 200, Issue 1.

15. Spinal Protocol:
• Sagittal T1 & STIR or fs T2 sequences
• If gadolinium administration is performed, T1-weighted sequences
with fs. should be obtained in the sagittal plane.
• - + Axial slices: for assessment of the posterior spinal elements.
• - + Coronal slices: for assessment of the costovertebral,
costotransverse, and facet joints.
Clarissa Canella, Bruno Schau, Elisio Ribeiro, Bruna Sbaffi and Edson Marchiori 2013: MRI in Seronegative Spondyloarthritis: Imaging Features
and Differential Diagnosis in the Spine and Sacroiliac Joints, American Journal of Roentgenology, Volume 200, Issue 1.

16. Simple MRI Request for SpA
whole-body of 1.0 or 1.5 Tesla MRI:
• SIJ:
• Semi-coronal at least 10–12 slices & axial oblique T1 & STIR or fs.T2 (+ gadolinium
with doubt or high suspicion)
• - + axial oblique.
• Spine:
• Sagittal T1 & STIR or fs T2 (+ gadolinium with doubt or high suspicion)
• - + Axial T1 & STIR or fs T2
• - + Coronal T1 & STIR or fs T2

17. Typical MRI Lesions

20. DD

21. Simultaneous radiography shows
definite chronic changes in the
form of erosion and joint space
widening (arrow) with some
subchondral sclerosis in the iliac
bone.

22. Chronic changes
Semi-coronal T1 FS image clearly shows
erosion corresponding to the right sacroiliac
joint (arrow). The semi-axial STIR image
demonstrates accompanying inflammation in
the surrounding bone (arrow).

23. Mixture of joint space and osseous
inflammation
Semi-coronal and semi-axial T1 FS after
intravenous Gd. contrast showing
enhancement in the joint space (black
arrow) as well as in the adjacent bone
(white arrow).

24. Mixture of joint space and osseous
inflammation
Semi-coronal and semi-axial T1 FS after
intravenous Gd. contrast showing
enhancement in the joint space (black
arrow) as well as in the adjacent bone
(white arrow).

25. Reactive arthritis
Early MR changes of the SIJs are usually
confined to the distal part of the joint
containing synovia. In transient arthritis
the MR abnormalities consist of uni- or
bilateral BMO.
Chronic changes such as erosion and
fatty deposition are usually lacking. The
changes may therefore heal without
sequels. There is always a risk of
recurrent episodes of inflammation and
the disease may transform into a chronic
stage. The imaging features can then be
AS-like except that chronic spinal
changes often present more voluminous
new bone formation than seen in AS.
Semi-coronal T1-weighted image shows
erosion of the joint facts (arrows).

26. Enteropathic arthropathy
Often presents more pronounced changes in the ligamentous part of the joint than seen
in other forms of SpA.
often heals with new bone formation.
New bone formation can therefore be seen later in the disease. It is best visualised by CT.

27. DD ??

28. DD ??
blurred joint
facets of lt SIJ

31. Septic sacroiliitis
www.spa-imaging.org

32. 40-year-old woman with
infectious sacroiliitis.
Axial fat-suppressed
gadolinium-enhanced T1-
weighted MR image of
sacroiliac joints shows
bone marrow
enhancement of sacrum
(white solid arrows),
irregularity of articular
space of left sacroiliac
joint (asterisks), abscess
(open arrows), and
enhancement of adjacent
soft tissue (black solid
arrows).
Clarissa Canella, Bruno Schau, Elisio Ribeiro, Bruna Sbaffi and Edson Marchiori 2013: MRI in Seronegative Spondyloarthritis: Imaging Features
and Differential Diagnosis in the Spine and Sacroiliac Joints, American Journal of Roentgenology, Volume 200, Issue 1.

33. 27-year-old man,
showing erosions of
the right sacroiliac
joint and
demarcation of the
cortex of the right
ischial tuberosity

35. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3489219/

36. Osteitis condensans ilii

38. •Brown tumours
Hyperparathyroidism
http://radiopaedia.org/articles/hyperparathyroidism
Henry Knipe, Frank Gaillard., et al.

39. 37 years old male patient with 2 years history of
inflammatory & mechanical LBP

40. 37 years old male patient with 2 years history of
inflammatory & mechanical LBP

43. Unilateral Sacroiliitis
• TB
• Brucella
• Other septic arthritis
Bilateral and symmetric
• Ankylosing spondylitis
• Inflammatory bowel disease
Bilateral and asymmetric
• Rheumatoid arthritis
• Psoriasis
• Reiter’s
• Gout (rare cause)
http://learningradiology.com/notes/bonenotes/sacroiliitispage.htm#sthash.QoltKFBb.dpuf

44. Conclusion
Apply ASAS definition of MRI sacroiliitis
Follow criteria in diagnosis not only clinical sense
In doubt of infective sacroiliitis DONOT forget axial oblique
sections with gadolinium enhancement

45. Questions