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Magnetic resonance imaging findings in the normal pediatric sacroiliac joint space that can simulate disease
Nele Herregods1, Lennart B O Jans2, Joel Paschke3
1Department of Radiology and Nuclear Medicine, Ghent University Hospital, C. Heymanslaan 10, 9000, Ghent, Belgium. Nele.Herregods@uzgent.be.
Insights
Most children
Area of Science:
- Pediatric radiology
- Musculoskeletal imaging
- Rheumatology
Background:
- Active sacroiliitis on MRI shows joint fluid and enhancement.
- The prevalence of these findings in healthy children is not well-established.
Purpose of the Study:
- To characterize normal MRI findings of pediatric sacroiliac joints.
- To differentiate normal variations from active inflammation.
Main Methods:
- Prospective MRI study of 251 children (119 boys, 132 girls).
- Utilized T1-weighted and STIR sequences; post-gadolinium sequences were available in a subset.
- Radiologists scored sacroiliac joint space signal intensity and enhancement.
Main Results:
- 74.7% of pediatric sacroiliac joints showed increased STIR signal; 18.4% had fluid-like signal.
- Girls peaked earlier (10 years) than boys (12 years) for signal intensity.
- Thin, rim-like post-contrast enhancement was common, without focal or intense enhancement.
Conclusions:
- Mild STIR signal and thin rim-like enhancement are common in pediatric sacroiliac joints.
- These findings are likely related to cartilage and should not be mistaken for sacroiliitis.
Background:
Magnetic resonance imaging (MRI) features of active sacroiliac joint inflammation include joint space fluid and enhancement, but it is unclear to what extent these are present in normal children.
Objective:
To describe normal MRI appearances of pediatric sacroiliac joint spaces in boys and girls of varying ages.
Materials And Methods:
In this ethics-approved prospective study, 251 children (119 boys, 132 girls; mean age: 12.4 years, range: 6.1-18.0 years), had both oblique-coronal T1-weighted and short tau inversion recovery (STIR) sacroiliac joint MRI. Of these, 127 were imaged for other reasons and had asymptomatic sacroiliac joints ("normal cohort") while 124 had low back pain with no features of sacroiliitis on initial clinical MRI review ("low-back-pain cohort"). Post-gadolinium T1-weighted sequences were available in 16/127 normal and 124/124 low-back-pain subjects. Three experienced radiologists scored high signal in the sacroiliac joint space on STIR (score 0=absent; 1=high signal compared to normal bone marrow present anywhere in the joint but not as bright as fluid [compared to vessels, cerebrospinal fluid]; 2=definite fluid signal in part of the joint; 3=definite fluid signal, entire vertical height, majority of slices) and, when available, joint space post-contrast enhancement (0=no high signal/enhancement; 1=thin, symmetrical, mildly increased linear high signal present in the joint space; 2=focal, thick or intense enhancement). Associations between joint signal scores, age, gender and sacral apophyseal closure were analysed.
Results:
Increased signal on STIR (score 1-3) was present in 74.7% of pediatric sacroiliac joint spaces, as intense as fluid in 18.4%. There was no significant difference in proportion by gender, side or cohort, but girls showed peak signal earlier than boys (10 years old vs. 12 years old, respectively). On post-gadolinium T1-weighted sequences, a thin rim of increased signal was nearly universally seen in sacroiliac joint spaces without focal, intense or thick post-contrast enhancement.
Conclusion:
Sacroiliac joint spaces of most children demonstrate mildly increased signal on STIR, compared to normal bone marrow, and thin rim-like enhancement on post-contrast T1 images, likely related to cartilage. These findings should not be confused with sacroiliitis.
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