Atypical and less-common imaging presentations of chronic nonbacterial osteitis in children: a pictorial review.

Chronic nonbacterial osteitis (CNO), including its multifocal form, chronic recurrent multifocal osteomyelitis (CRMO), is an autoinflammatory sterile bone disorder with protean imaging features across the appendicular and axial skeletons in children and adolescents. Magnetic resonance imaging (MRI)-particularly whole-body MRI (WBMRI)-is pivotal for diagnostic imaging, mapping total inflammatory burden, demonstrating multifocality, and monitoring treatment response. Radiographs are frequently normal early in the disease. Beyond the classic metaphyseal pattern, we demonstrate atypical presentations that often mimic other conditions, such as infection or malignancy: progressive collapsing vertebral disease with vertebra plana, hip arthritis due to involvement of intra-articular metaphyseal equivalents, myositis not related to areas of active osteitis, extensive periosteal new bone in long bones, pseudotumoral lesions of flat bones, and craniofacial involvement. This pictorial review provides a structured diagnostic approach to prompt consideration of CNO, facilitate differentiation from bacterial osteomyelitis and bone tumors in the differential diagnosis, and support early, targeted anti-inflammatory therapy.