[Residual and reconverted hematopoietic bone marrow in the distal femur. Spin-echo and opposed-phase gradient-echo...

The distal femur contains usually only fatty marrow in the adult. We investigated the incidence of areas of residual and reconverted hematopoietic marrow in the distal femur in a series of 50 adult patients using conventional spin-echo and opposed-phase gradient-echo MR images. Zones with intermediate to low signal intensity in both sequences representing hematopoietic marrow within high signal intensity fatty marrow were observed in 17 of the 50 patients. Opposed-phase gradient-echo sequences demonstrated significantly greater red-yellow marrow contrast than conventional spin-echo sequences. Residual red marrow may represent a biologic variation of the normal adult pattern of red-yellow marrow distribution in women of menstruating age. Reconverted red marrow appears to be related to increased erythrocyte demand. It should not be mistaken for bone marrow malignancy. Absence of epiphyseal involvement, cortical destruction and soft-tissue mass in residual and reconverted hematopoietic marrow are helpful differential criteria.