Common incidental findings on sacroiliac joint MRI in children clinically suspected of juvenile spondyloarthritis

PURPOSE: To determine the prevalence of incidental findings on sacroiliac (SI) joint MRI in children clinically suspected of Juvenile Spondyloarthritis (JSpA). METHODS: In this retrospective multi-center study of 540 children clinically suspected of JSpA who underwent MRI of SI joints from February 2012 to May 2018, the prevalence of sacroiliitis and other incidental findings was recorded. RESULTS: In 106/540 (20 %) children MRI features of sacroiliitis were present. In 228 (42 %) patients MRI showed at least one incidental finding other than sacroiliitis. A total of 271 abnormal findings were reported. The most frequent incidental findings were at lumbosacral spine (158 patients, 29 %) and hip (43 patients, 8 %). The most common incidental finding was axial degenerative changes, seen in 94 patients (17 %). Other less frequent pathologies were: simple (bone) cyst in 15 (2,8 %) patients; enthesitis/tendinitis in 16 (3 %) patients; non-specific focal bone marrow edema (BME) away from SI joints in 10 (1,9 %) patients; ovarian cysts in 7 (1,3 %) patients; BME in the course of chronic recurrent multifocal osteomyelitis (CRMO) in 4 (0,7 %) patients; muscle pathology in 4 (0,7%) patients; benign tumors in 3 (0,6 %) patients; (old) fractures in 3 (0,6 %) patients; bony apophyseal avulsion in 2 (0,4 %) patients and malignant tumors in 2 (0,4 %) patients. CONCLUSION: Incidental findings are common on MRI of the SI joints in children clinically suspected of JSpA, particularly at the lumbar spine and hips. They are seen even more frequently than sacroiliitis and can be relevant, as some will have clinical significance or require treatment.