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Normal subchondral high T2 signal on MRI mimicking sacroiliitis in children: frequency, age distribution, and relationship to skeletal maturity

  • Musculoskeletal
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Abstract

Objectives

To determine patterns of variation of subchondral T2 signal changes in pediatric sacroiliac joints (SIJ) by location, age, sex, and sacral apophyseal closure.

Methods

MRI of 502 SIJ in 251 children (132 girls), mean age 12.4 years (range 6.1–18.0), was obtained with parental informed consent. One hundred twenty-seven out of 251 had asymptomatic joints and were imaged for non-rheumatologic reasons, and 124 had low back pain but no sign of sacroiliitis on initial clinical MRI review. After calibration, three subspecialist radiologists independently scored subchondral signal changes on fat-suppressed fluid-sensitive sequences from 0 to 3 in 4 locations, and graded the degree of closure of sacral segmental apophyses. Associations between patient age, sex, signal changes, and apophyseal closure were analyzed.

Results

Rim-like subchondral increased T2 signal or “flaring” was much more common at sacral than iliac SIJ margins (72% vs 16%, p < 0.001) and was symmetrical in > 90% of children. Iliac flaring scores were always lower than sacral, except for 1 child. Signal changes decreased as sacral apophyses closed, and were seen in < 20% of subjects with fully closed apophyses. Signal changes were more frequent in boys, and peaked in intensity later than for girls (ages 8–12 vs. 7–10). Subchondral signal in iliac crests was high throughout childhood and did not correlate with other locations.

Conclusions

Subchondral T2 “flaring” is common at SIJ of prepubertal children and is generally sacral-predominant and symmetrical. Flaring that is asymmetrical, greater in ilium than sacrum, or intense in a teenager with closed apophyses, is unusual for normal children and raises concern for pathologic bone marrow edema.

Key Points

• A rim of subchondral high T2 signal is commonly observed on MRI at pediatric sacroiliac joints, primarily on the sacral side before segmental apophyseal closure, and should not be confused with pathology.

• Unlike subchondral signal changes elsewhere, high T2 signal underlying the iliac crest apophyses is a near-universal normal finding in children that usually persists throughout adolescence.

• The following patterns are unusual in normal children and are suspicious for pathology: definite iliac flaring, iliac flaring more intense than sacral flaring, left-right difference in flaring, definite flaring of any pattern in teenagers after sacral apophyseal closure.

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Abbreviations

ASAS:

Assessment of Spondyloarthritis International Society

BME:

Bone marrow edema

JSpA:

Juvenile spondyloarthritis

LBP:

Low back pain

MRI:

Magnetic resonance imaging

SIJ:

Sacroiliac joint

STIR:

Short tau inversion recovery

TE:

Echo time

TI:

Inversion time

TR:

Repetition time

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The authors state that this work has not received any funding.

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Correspondence to Nele Herregods.

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Guarantor

The scientific guarantor of this publication is Herregods Nele.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

One of the authors (Stefanie L. De Buyser, Biostatistics Unit, Faculty of Medicine and Health Sciences Ghent University) has significant statistical expertise.

Informed consent

Written informed consent was obtained from all subjects (patients and their parents) in this study.

Ethical approval

Institutional Review Board approval was obtained.

Study subjects or cohorts overlap

Some study subjects or cohorts have been previously reported in some of our previous reports on other topics (77/251 patients). We have published on pediatric patients with low back pain or established spondyloarthritis. This is our first manuscript focused on normal children with no history of back pain. This manuscript focuses on new data on a unique group of 127 “normal” patients, with asymptomatic sacroiliacal joints who were being imaged for non-rheumatologic conditions, of whom we have not published before. We compare findings in this group to a set of 124 “LBP” patients whom we have previously analyzed, who did not show features of sacroiliitis at initial clinical MRI review but who presented with inflammatory back pain symptoms. The high similarity we note in physiologic findings between findings in the normal and “LBP” cohorts is an important observation that can help guide study design for future research in this field.

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Herregods, N., Jans, L.B.O., Chen, M. et al. Normal subchondral high T2 signal on MRI mimicking sacroiliitis in children: frequency, age distribution, and relationship to skeletal maturity. Eur Radiol 31, 3498–3507 (2021). https://doi.org/10.1007/s00330-020-07328-0

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