Normal paediatric bone marrow: Magnetic resonance imaging appearances from birth to 5 years

Introduction Bone marrow (BM) assessment is an important aspect of paediatric MRI, with the marrow cavity visible on almost every clinical MR examination. In practice, however, assessment for marrow infiltration in paediatric patients can be challenging. Our aim was to review the MRI appearance of normal BM from 0 to 5 years. Methods Consecutive body MR examinations over 7 years were retrospectively reviewed in patients aged 0–5 years. Patients with anticipated BM abnormality were excluded. All patients had imaging of the spine and/or pelvis with T1‐weighted (T1) ± T2 with fat saturation, post‐contrast T1‐weighted, diffusion‐weighted or out‐of‐phase sequences. Results Nineteen patients were included: nine (47%) infants, 11 (58%) boys, mean age 18.2 months (range 1 day to 3 years and 10 months). On T1 imaging, 69% infant marrow sites and 24% in children >1 year were isointense, the remainder were hyperintense. One hundred per cent BM was T2 fat saturation hyperintense. Enhancement following contrast was seen in 16% of BM sites. Restricted diffusion was seen in 100% infant BM and 50% BM in children >1 year. On out‐of‐phase imaging, no signal loss was seen in infants, and 21% BM in children >1 year showed signal loss. Conclusion Due to normal age‐related differences in BM histology, MRI for marrow assessment in infants and young children can be misleading and may mimic marrow infiltration.