CT and MRI features of SAPHO syndrome: a report of 6 cases

To investigate the CT and MRI features of synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome, aiming to improve the recognition of this disease by clinicians and radiologists and to reduce misdiagnosis and missed diagnosis.

Clinical and imaging data of 6 patients with confirmed SAPHO syndrome hospitalized in our hospital from November 2011 to August 2025 were retrospectively analyzed. The cohort included 4 males and 2 females, aged 26-70 years (mean 44.5 ± 19.2 years). All patients underwent both CT and MRI examinations. The distribution of lesions and the imaging features on CT and MRI were analyzed.

The anterior chest wall was involved in all 6 patients, including costosternal joint involvement in 6 (100%) and sternoclavicular joint involvement in 4 (66.7%). The typical "bull head sign" was observed in 4 patients. Among a total of 144 vertebrae examined in the 6 patients, CT detected 34 affected vertebrae (23.6%) and MRI detected 51 affected vertebrae (35.4%), predominantly in the thoracic spine. Characteristic CT signs included the "bright corner sign", "half-circle sign", and "round sign". Characteristic MRI signs included the "kissing sign" (present in 80.0% of continuously involved vertebrae) and bone marrow edema. CT was superior in detecting osteosclerosis, while MRI was superior in detecting bone marrow edema. Bilateral sacroiliac joint involvement was present in 3 cases, and the hip joint was involved in 1 case. Three cases had been misdiagnosed as ankylosing spondylitis, psoriatic arthritis, or spinal metastases.

Skeletal lesions of SAPHO syndrome predominantly involve the anterior chest wall (the "bull head sign" is characteristic) and the thoracic spine (with continuous vertebral involvement, showing the "bright corner sign" and "kissing sign"). The combined use of CT and MRI facilitates comprehensive evaluation of lesions, and identification of skin lesions can improve the recognition of this disease.