PED Case 7: Hematopoitic red marrow
Publication Date: 20170629
Patient is a 9-year-old girl with history of right knee osteomyelitis presenting now with fever and left knee pain. She developed sudden onset fever up to 40°C with accompanying left knee discomfort. Mother stated that this presentation is similar to how her previous episodes of right knee osteomyelitis presented. Patient went to her pediatrician where rapid strep test came back positive. Then patient additionally went to her pediatric orthopedist and was advised to go to the ED for osteomyelitis workup. At interview, she appeared comfortable in bed, however did endorse anterior knee pain and can bear weight on the left lower extremity (LLE).
AP (Fig. 1A) and lateral (Fig. 1B) radiographs of the knee are normal. On MRI (Figs. 2A-C) there is low T1 signal in a “flame shaped” (vertical orientation) in the metaphysis. No appreciable associated high-signal on coronal STIR images with mild patchy enhancement on post-contrast images. No appreciable surrounding soft tissue abnormalities. The cortex appears intact.
Hematopoitic red marrow
Heterogenous red marrow is often seen in the pediatric population as their bone marrow converts. The adult pattern of marrow is usually developed around age 25. Red to yellow conversion usually starts peripherally in the phalanges and progresses centrally. In the long bones it starts at the eipiphysis, followed by the diaphysis, then distal metaphysis and lastly the proximal metaphysis. It is important to be familiar with this in order to not confuse it for a pathologic condition. Osteomyelitis and marrow diseases can have somewhat similar appearances. The lack of surrounding soft tissue changes and clinical picture will often help differentiate osteomyelitis and the pattern of bone marrow signal will help differentiate from a marrow disease.
- Chan BY, Gill KG, Rebsamen SL, Nguyen JC. MR Imaging of Pediatric Bone Marrow. RadioGraphics 2016 36:6, 1911-1930. PMID: 27726743 DOI: 10.1148/rg.2016160056