Inflammatory Spondyloarthritis

Imaging ¹

Findings

Divide Finding and changes into acute vs chronic and Spinal Changes and SIJ.

	Acute ('Inflammatory')	Chronic ('Structural')
Sacro-Iliac Joints	Bone Marrow Oedema	Fat Metaplasia Erosions Sclerosis Ankylosis
Spine	Bone Marrow Oedema in bodies ('Spondylitis') Bone Marrow Oedema in Facet, Costovertebral, Costotransverse joints ('Arthritis')	Fat Metaplasia Sclerosis Ankylosis.

Modality Gold Standards

MRI best for Active Inflammatory changes and for fat metaplasia in chronic change.
CT and/or Radiographs for Erosions and Sclerosis.
Radiographs still for New Bone Formation and Ankylosis.

"In daily practice, recognition of imaging findings is used for diagnosing patients with axSpA, but quantification of these lesions is not necessary."

Scoring Systems for Imaging. ¹

Sacro-Iliac Joints

Conventional Radiographs

New York Criteria (1966, modified 1984) ²

Grade	Definition
0	Normal
1	Suspicious changes
2	Minimal abnormalities: Small localized areas with erosion or sclerosis, without alteration in the joint width
3	Unequivocal abnormality: Moderate or advanced sacroilitis with 1 or more signs of erosions, sclerosis, widening, joint space narrowing, or partial ankylosis.
4	Severe changes: Total Ankylosis

Modified New York Criteria : Diagnosis of AS based on Grade 2 changes bilaterally or Grade 3 or 4 unilaterally with specific clinical symptoms suggestive (ie Inflammatory sounding back pain / limitation in movement of spine.). This could mean a 7 to 10 year wait for a diagnosis.

MRI

Nearly all systems for Active inflammation use Semicoronal STIR images.
( post Gd T1fs are an alternative. Signal increase here = Vascularization = thus "osteitis" ).
Chronic / Structural changes use T1-weighted. 3-4mm slice thickness.

(Active) Inflammatory Sacroiliac joint lesions.

Multiple systems most of which preform fairly similarly and even a Gestalt Score of 0-3 per SIJ was good. ³

Use Berlin Criteria:
Score each quadrant of each SIJ 0 to 3. Based on Bone marrow oedema on STIR

	Grade 0	Grade 1	Grade 2	Grade 3
Bone Marrow Oedema in each quadrant SIJ area	Absent	<33%	33-66%	>66%

Thus Total score = (4 x 3) x 2 = 0 to 24.
Note this system avoids conversations about erosions yes or no as a measure of activity or soft tissue change.

(Chronic) Structural Sacroiliac joint changes.

Same applies, here there are multiple systems with slightly different ways of doing this.
Berlin Criteria uses a mixed way of doing this with some dichotomy and some semi-qualitative.

	Grade 0	Grade 1	Grade 2	Grade 3
Erosions per quadrant	Absent	Minor (1 or 2)	Moderate (3 to 5)	Multiple (Confluent)
Fatty Bone Marrow Deposition (FMD) per quadrant	Absent	Present
Sclerosis per joint	Absent	Present
Ankylosis	Absent	Present

Thus Total score = ((4 x 3) x 2) + ((4 x 1) x 2) + 1 + 1 = 0 to 64.
Which is a dog's breakfast and not at all rational.
So suggest Jackdaw should use vague total measure of each joint but explicitly stating each of the criteria.

Spine

Conventional Radiographs

Several scoring systems mostly focussed on hyperproliferative aspects in AS and PsA.
Most use laterals of the Lumbar spine. Some add on Hips or Thoracic spine or AP views. Tend to measure using 0-3 scores looking at:

1. Erosions
2. Squaring
3. Sclerosis
4. Syndesmophytes at anterior vertebral edges.

Though others will add in posterior edge etc

MRI

Use 3-4 mm Sag STIR for active disease and Sag T1 for chronic change. Post Gd Sat T1fs "no additional benefit for superior assessment of disease activity" ¹

(Active) Inflammatory Spinal joint lesions.

Several systems in use. Most have good performance for active disease and change and for reliability. All but 1 out of 7 looks at the posterior elements for signs of inflammation. Use Discovertebral Unit (DVU) = Bottom 1/2 of vertebral body + Disc + Upper 1/2 of lower vertebral body, starting at C2/3. There are 23 of them.

Berlin Criteria

	Grade 0	Grade 1	Grade 2	Grade 3
Bone Marrow Oedema in DVU area.	Absent	<25%	25-50%	>50%
Bone Marrow Oedema in Posterior Segment per DVU	Absent	Minor	Severe

Might just do 0-3 for anterior bodies but only mention if there is stuff in the posterior parts.

(Chronic) Structural Structural joint changes.

Several systems but little in way of usage as plain films are still better. And can be complicated with ASspiMRI-c producing a scale from 0 to 138.

But, they still concentrate on:

1. Fat metaplasia (FMD)
2. Erosion
3. Syndesmophytes
4. Ankylosis

and some include:

1. Sclerosis
2. Squaring off

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Paediatric Considerations⁴

Juvenile spondyloarthropathy = group of related inflammatory disorders, onset in childhood of adolescence.
Presentation is more with peripheral arthritis and enthesitis of pelvis and leg in early disease and generally SIJitis later in the course.

"(SIitis is)..more challenging to diagnose compared with adults due to normal physiological changes."⁴

Protocol for SIJ MRI.

Lots of protocols out there (but for adults):

• ASAS 2009 = Semicoronal T1/STIR.
• ASAS-SPARTAN 2021.

But for children there is the: ESSR-ESPR paper for SIitis in JIA⁵

This was:

• Semicoronal T1 / STIR ( or fat suppressed T2 )
• Axial STIR ( or fat suppressed T2 )
• and optional fat sat T1 post Gd semicoronal and axial.

I think it should be:

1. Semicoronal STIR
2. Semicoronal T1
3. Ax STIR of the whole pelvis ( to look at the hips and enthesitis ).

But for structural lesions then a sequence for better optimisation of the bone-cartilage interface is considered important, mostly to look at erosions.
This might mean T1fs 2D or 3D or perhaps DESS.

Imaging Characterisations in Children.

No paediatric scoring system or agreement like for ASAS or SPARCC or OMERACT for SIJitis "Developing reliable pediatric-specific definition for sacro-ilitis is a difficult task"

Active inflammatory lesions

Count bone marrow oedema (BMO), joint fluid, joint enhancement, inflammation in an erosion cavity, capsulitis and enthesitis.
But Bone marrow oedema is the key feature for diagnosing SIitis.
However Sens/Spec = 0.26 / 0.97. So, less sensitive but more specific than for adults.

Look for Enthesitis
Predicts predicts SIitis on follow up MRI.
Look at symphysis pubis, rami, iliac crests, ischia, anterior superior and inferior iliac spines, vertebral posterior elements and any other muscle insertions.

Synovitis in large joints is a pain in the arse in children.
Limited studies but normal kids have synovial enhancement in knees at least and tiny/small effusions. ⁶ JIA seems to be associated with thickening >2mm and with effusions >3mm at least.
So Gd is useful really at seeing the synovium and measuring it accurately but clear that the degree of enhancement is not that helpful

Structural lesions

Seen generally later, on semicoronal T1 sequences.
Are: Erosions, sclerosis, fat lesions (metaplasia), backfill(?) and ankylosis.
Seen less often in children.

Definitions from JAMRIS-SIJ Scoring System. (JIA working group in OMERACT)

Features	Definitions
	Active Inflammation
Bone Marrow Oedema	An ill-defined area of high bone marrow signal intensity within the subchondral bone of the ilium or sacrum on fluid-sensitive images
Bone marrow Oedema Intensity	Hyperintensity of the marrow edema, using the brightest presacral veins as reference
Bone marrow oedema depth	Continuing increased signal of depth ≥ 5 mm/ ≥ 1 cm from the articular surface
Capsulitis	High signal on fluid-sensitive and/or post-contrast enhancement involving the sacroiliac joint capsule
Joint Space Inflammation (JSI)	Increased signal on fluid-sensitive or contrast-enhanced T1-weighted images within the joint space of the cartilaginous portion of the sacroiliac joint.
Enthesitis	High signal in bone marrow and/or soft tissue on a fluid-sensitive sequence or a contrast-enhanced T1-weighted sequence at sites where ligaments and tendons attach to a bone
	Structural Lesions
Sclerosis	A substantially wider than normal area of low subarticular bone signal on T1-weighted and fluid-sensitive images (≥ 5 mm in adolescents)
Erosion	Bony defect (or irregularity with associated bone marrow edema, sclerosis, or fatty lesion) at the osteochondral interface involving both contour and signal on both T1-weighted and fluid-sensitive images
Fat lesion	Increased homogenous signal intensity on T1-weighted non- fat suppressed image in subchondral bone with a distinct border
Backfill	A bright signal on a T1-weighted sequence in a typical location for an erosion, with signal intensity greater than normal bone marrow, and meeting the following requirements. 1. It is associated with complete loss of the dark appearance of the subchondral cortex at its expected location. 2. It is clearly demarcated from adjacent bone marrow by an irregular band of dark signal reflecting sclerosis at the border of the original erosion.
Ankylosis	Presence of signal equivalent to regional bone marrow continuously bridging a portion of the joint space between the iliac and sacral bones

“in comparison to physiological changes normally seen in MRIs of age and sex matched children, and visible in two planes where available”

Gadolinium

Most recent papers suggest only limited role in DETECTION of active synovitis in children ⁴.
Might be helpful for ambiguous cases: Uncertain findings on STIR, or to differentiate joint fluid from joint space.

Pitfalls in the Assessment of pediatric Sacroilitis.

Bony Anatomy

Primary centres fuse by ~ 7 yrs. Multiple small apo and epi-physes

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1. Baraliakos X, Braun J. Imaging Scoring Methods in Axial Spondyloarthritis. Rheum Dis Clin N Am 42(2016)663-678 http://dx.doi.org/10.1016/j.rdc.2016.07.006 ↩↩↩

2. van der Linden S, Valkenburg H et al, Evaluation of diagnostic Criteria for ankylosing spondylitis. Arthritis Rhem 1984;27(4):361-8 ↩

3. Landewe R, Herrman K et al Scoring sacroiliac joints by MRI: A multi-reader reliability study. J Rheumatol 2005:32(10):2050-5 ↩

4. Herregods N, Anisau A et al. MRI in Paediatric sacroilitis, what radiologists should know. Pediatric Radiology 2023 https://doi.org/10.1007/s00247-023-05602-z ↩↩↩

5. Hemke R, Herregods N, Jaremko JL et al (2020) Imaging assessment of children presenting with suspected or known juvenile idiopathic arthritis: ESSR-ESPR points to consider. Eur Radiol 30:5237–5249 ↩

6. Hemke R et al. Contrast-enhanced MRI findings of the knee in healthy children; establishing normal values Eur Radiol (2018) 28:1167–1174 DOI 10.1007/s00330-017-5067-6 ↩