-Look to the spine in T1 sequence, if the body of the spine is hyper intense, this means that the bone marrow is yellow marrow, while if the body is intermediate, so the marrow present is red marrow.
-This changes depend on the age of the patient, as in children the red bone marrow is dominant while in old age the yellow marrow is dominant.-Causes of diffuse hypo intense bone marrow signal in T1 sequence:
1-Multiple myeloma.
2-Lymphoma which is much more common with non Hodgkin' lymphoma than Hodgkin's lymphoma.
3-HIV.
-Marrow depletion disorders such as after irradiation or chemotherapy resulting in loss of normal red marrow and thus diffusely markedly fatty signal (hyper intensity ) on all pulse sequences.
Immediately after therapy, bone marrow will be hypo intense due to necrosis. Then after 3-6 weeks, start to have hyper intensity due fat formation.
The end result of this cannot be differentiated from aplastic anemia.
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| The homogeneously and intensely bright signal on T1w images in this 69 year old woman is compatible with a marrow depletion disorder. This woman had undergone chemotherapy, but the pattern can not be differentiated from aplastic anemia by MR imaging. |
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| Bone marrow depletion sharply delineated by the radiation portal (site of receiving irradiation )in this 52 year old man. Note the fatty replacement of the lower three vertebral bodies (arrowheads). |
Conclusion
MR is a very sensitive technique for evaluating bone marrow. Opportunities for such evaluation abound as portions of the marrow can be evaluated on nearly every MR study performed. Knowledge of the signal on the variety of pulse sequences and pattern of marrow in the normal spine is essential knowledge in deciding what is potentially pathologic and what is not. The conversion of normal red marrow to yellow marrow and the reconversion back to hematopoietically active marrow under physiologic stress is a common occurrence but highlights one weakness of MR, its lack of specificity without clinical information. In a patient such as the test case who demonstrates diffusely low T1w marrow signal on MR, the differential diagnosis is long and includes many benign reconversion conditions, malignant myeloproliferative disorders and abnormalities of the supporting reticulum.
MR is a very sensitive technique for evaluating bone marrow. Opportunities for such evaluation abound as portions of the marrow can be evaluated on nearly every MR study performed. Knowledge of the signal on the variety of pulse sequences and pattern of marrow in the normal spine is essential knowledge in deciding what is potentially pathologic and what is not. The conversion of normal red marrow to yellow marrow and the reconversion back to hematopoietically active marrow under physiologic stress is a common occurrence but highlights one weakness of MR, its lack of specificity without clinical information. In a patient such as the test case who demonstrates diffusely low T1w marrow signal on MR, the differential diagnosis is long and includes many benign reconversion conditions, malignant myeloproliferative disorders and abnormalities of the supporting reticulum.
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