(Fig 5-B.03) Hematopoietic (Red) Marrow

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📌 Hematopoietic (Red) Marrow: Marrow Reconversion
✅ Definition:
Marrow reconversion refers to the process whereby mature fatty marrow is replaced by hematopoietic marrow when the existing marrow can no longer meet the need for hematopoiesis.
✅ Causes: Demand for increased hematopoiesis occurs in:
Anemias, such as sickle cell anemia and thalassemia
Marrow-stimulating medications
Marrow replacement disorders
High altitudes
Smokers
Obese patients
✅ Progression:
Hyperplasia of hematopoietic marrow occurs in the reverse sequence of normal marrow maturation, commencing proximally in regions that are composed of predominantly red marrow and progressing distally to areas of fatty marrow.
Therefore, hematopoietic marrow hyperplasia initially affects the axial skeleton, followed by the appendicular skeleton.
✅ Imaging Characteristics:
Because red marrow contains intermixed fat, it typically has T1-weighted signal intensity (SI) that is higher than muscle.
However, in cases of profound red marrow reconversion, red marrow may be difficult to differentiate from malignancy.
📌Hematopoietic Marrow in Children
✅ Distribution:
Residual red marrow is frequently present in the metaphyseal and adjacent diaphyseal portions of the femur and tibia in children, and may simulate abnormalities such as neoplastic infiltration, stress reaction, and contusion.
✅ Imaging Characteristics:
The regions of normal red marrow are longitudinally oriented with straight margins and have a base at or adjacent to the physis.
On T1-weighted images, they should always be of increased signal relative to muscle.
On T2-weighted images, the hematopoietic marrow is hyperintense due to its high water content with a signal that approximates that of muscle.
T1 and fat-suppressed proton density-weighted images show normal red marrow as hypointense on T1 and moderately hyperintense on proton density-weighted images. The red marrow has a striated and flame-shaped appearance in the metaphyses and diaphyses of the femur and tibia, typically sparing the epiphyseal regions.
References:
AJR 2010; 195-W200
AJR 2011; 197:1309-1321
MRI Web Clinic - October 2009 Developmental Variants
"Visualizing MSK Radiology: A Practical Guide to Radiology Mastery"
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