Why would Tibia have "Islands of Red Marrow?"
I have just had an MRI of my Right Tibia due to the potential for another stress fracture (this would make it # eight. I am 29 yrs old and we are still trying to figure out an underlying cause for my osteoporosis) My question is that my MRI states the following..."There are foci of mildly decreased T1 signal and increased STIR/T2 signal within the proximal shaft of the tibia. These foci are consistant with islands of red marrow."............what are "islands of red marrow"??? The MRI did not show a stress fracture, would these islands of red marrow be causing my pain (terrible ache and pain with weight baring)? I am waiting on a call back from my ortho, just thought I would try to get as much info as possible. Thanks for your help in advance, Jen
The marrow sinuses are lined by an endothelium, of which the cell juncture is undulated and overlapping. The endothelium is backed by a thin sheet of adventitial cells which is discontinuous because of large perforations. Mature blood cells pass through the discontinuous parts of the adventitial cells and then penetrate the endothelium at its parajunctional zone.
erythroblasts in an island may be in a uniform maturation stage or in a few different stages.
(Ref: Scan Electron Microsc. 1982;(Pt 1):445-53)
Normal bone marrow is divided into red and yellow marrow, a distinguished on the grounds of how much fat it contains. Red marrow is composed of 1) haematopetic cells 2) supporting stroma 3) reticulum (phagocytes and undifferentiated progenitor cells) 4) scattered fat cells and 5) a rich vascular supply. Yellow marrow, conversely has all the same constituents as red, except that fat cells make up the vast majority, with resulting poor vascularity.
Distribution varies with age and from one individual to another, but should be symmetric.
During infancy red marrow occupies the entire ossified skeleton except for epiphyses and aphophyses. Gradually red marrow 'retreats' centrally, such that by adulthood it is essentially confined to the axial skeleton (pelvis, spine, shoulder girdle, skull). Frequently the proximal humeri and neck of femurs have residual red marrow.
In addition, islands of red marrow may be seen anywhere in the skeleton, typically in a subcortical distribution, often with central yellow marrow giving it a bull's eye appearance on axial imaging. Additionally red marrow is found in subchondral crescents again of the proximal humerus and femur.
Yellow marrow can also be seen focally in vertebra around the basivertebral vein, adjacent to degenerative disc disease and Schmorl's nodes, and within haemangiomas.
• T1W sequences: ALWAYS slightly hyperintense to muscle and disc. (due to scatted fat cells)
• T2W sequences: can be difficult to distinguish from yellow marrow as both are somewhat hyperintense.
• STIR sequences: Red marrow remains hyperintense, c.f. yellow marrow which is saturated out.
• Follows subcutaneous fat on all sequences
The MRI appearance is variable:
• Normal red marrow appearance (10 - 25% of all leukaemic patients will have normal appearing marrow)
• Abnormal distribution of what appears to be normal red marrow.
• Abnormal signal from red marrow in a normal distribution
• Abnormal signal and distribution
The abnormal signal is due to replacement of the small amounts of fat cells normally found in red marrow, such that T1WI will decrease to or bellow the signal from disc or muscle. T2WI signal is more variable, but will in general increase when compared to muscle.
(Kindly refer: http://radiopaedia.org/articles/bone_marrow)
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