Chronic recurrent multifocal osteomyelitis (CRMO) and synovitis, acne, pustulosis, hyperostosis, osteitis (SAPHO) syndrome are related disorders of unknown aetiology which occur in children and adults, and represent a combination of skin and musculoskeletal manifestations which may mimic infection or neoplastic disease, both clinically and radiologically. Clinically, the conditions present with an insidious onset of bone pain and swelling which may be recurrent and last over decades.

The radiological features are primarily due to a combination of hyperostosis, resulting in cortical thickening/bone expansion, and osteitis which manifests as bone marrow oedema on MRI and medullary sclerosis on radiographs and CT. The common sites of occurrence include the anterior chest wall (especially the sternoclavicular region), the spine, the major long bones and the pelvis. With experience, the diagnosis can confidently be made based on the characteristic clinical and imaging findings, without the requirement for needle biopsy.

Educational aims:
• To raise awareness of these conditions as possible differential diagnoses for malignant processes
• To illustrate the classical imaging features
• To provide an imaging algorithm which should allow a confident non-invasive diagnosis

References:
• Lyer RS, Thapa MM, Chew FS. Chronic recurrent multifocal osteomyelitis: review. AJR 2011; 196: S87-91.
• Depasquale R, Kumar N, Lalam RK et al. SAPHO: What radiologists should know. Clin Radiol. 2012; 67: 195-206.

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