Pediatric Marrow Conversion

  • Etiology: marrow starts out in the long bones as red (hematopoeitic) marrow and converts to yellow (fatty) marrow over first two decades, the last red marrow seen is in the proximal metaphysis
  • MRI:
    — Best assessed on T1WI, yellow (fatty) marrow similar to subcutaneous fat, red (hematopoietic) marrow equal or greater than skeletal muscle and intervertebral discs after infancy
    — Marrow conversion occurs from peripheral (appendicular) skeleton to central (axial) skeleton, from distal to proximal (early epiphyseal conversion), from diaphyseal to metaphyseal
    — Yellow marrow appears in the epiphysis within six months of ossification, in the diaphysis at 1-10 years, in the distal metaphysis at 10-15 years, in the proximal metaphysis in young adult

Radiology Cases of Marrow Conversion