[Vertebral involvement in SAPHO syndrome]

SAPHO syndrome (Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis) is characterized by a great variety of radiographic findings, including sclerosing osteitis, ivory vertebra, hyperostosis with paravertebral ossification, spondylodiscitis and even vertebral compression fractures. On the other hand, the MR imaging features are quite stereotypical with presence of entesopathy at the anterior vertebral corner similar to other spondyloarthropathies. In about 15% of cases, the entesophytes are limited to the anterior vertebral corner. In all other cases, it extends to involve the adjacent vertebral endplate, the anterior vertebral cortex or the adjacent vertebral corner through the disc annulus. As such, involvement of at least two adjacent vertebrae is present in about 30% of cases. The intervertebral disc may be narrowed, and, in 10% of cases, show intense T2W signal and postcontrast enhancement, simulating infections spondylodiscitis. The pseudo-infectious appearance is further increased in about one third of cases by the presence of an enhancing mass in the adjacent soft tissues. Therefore, these lesions may sometimes be difficult to differentiate from infectious spondylodiscitis and even tumors. An important differential diagnostic feature is the presence of lesions of varying ages on adjacent vertebral segments, with presence of characteristic entesopathy of a vertebral corner.