Purpose or Case Report: There are various conditions or diseases that may cause multiple bone marrow lesions in children or adolescents. Radiographically, lytic lesions may become apparent after loss of >50% of bone mineral content. Scintigraphy requires osteoblastic activity and is not specific. MRI has been increasingly employed for the investigation of diseases that involve the skeleton and for further delineation of radiographic findings in symptomatic children.
Purpose: To describe the MRI findings of entities resulting in multiple bone marrow lesions in children and provide a wide differential diagnosis.
Methods & Materials: MRI scans and records of children examined during the last 4 years for symptoms relevant to the musculoskeletal system or as further diagnostic workup of conditions that affect the bones were retrieved. All scans with more than one focal bone marrow lesion in a single bone or with polyostotic involvement were included. Final diagnosis was based on histological diagnosis and/or clinical evolution following conservative therapy.
Results: Diagnoses included: Metastatic diseases, LCH, lymphoma, CRMO, multifocal osteomyelitis, polyostotic fibrous dysplasia, multifocal Ewing’s Sarcoma, multifocal osteosarcoma, bone infarcts, bilateral Perthe’s disease, multiple stress fractures/reactions, multiple exostoses, multiple enchondromatosis syndrome, multifocal osteochondritis dissecans, bone marrow reconversion or hyperplasia, post radiation changes.
Parameters that were considered useful for the pre-biopsy diagnosis included radiographic appearances, known history, athletic activity/physiotherapy, synchronous or metachronous lesions, zone of transition, signal intensity, bilaterality or laterality with regard to midline as well as location in the bone (cortex or medulla, diaphysis, metaphysis or epiphysis).

Conclusions: MRI may significantly contribute to the diagnosis of conditions that cause multifocal bone marrow lesions in children. The differential diagnosis is wide and includes both malignant and benign entities.