MRI of Bone Marrow
MRI of Bone Marrow
John F. Feller
MRI is the imaging modality of choice for the hands and feet. There is then a “distal-to- The clinical advantages of STIR are due to
investigation of bone marrow disorders. proximal“ trend of conversion within the the following characteristics: (1) additive T1
Accurate interpretation of MR examinations bones of the extremities. Conversion also and T2 contrast; (2) marked fat suppression;
of bone marrow requires an understanding occurs at different rates within the same (3) a two-fold increase in the magnetization
of the anatomy, physiology, distribution, and bone. Within long bones, marrow converts range of spin-echo sequences. As a result,
conversion patterns of bone marrow. Tech- first in the diaphysis, then in the distal STIR images demonstrate extraordinarily
nical factors of the MR examination are also metaphysis, and finally in the proximal high contrast, conspicuousness, and
important. Common pathophysiologic path- metaphysis. sensitivity for the depiction of most types of
ways allow a useful classification of bone By age 25 years, the adult distribution of bone marrow pathology. The obvious
marrow disorders. bone marrow is attained which is drawbacks of this pulse sequence, however,
characterized by red marrow persisting in include relatively long imaging times, and a
BONE MARROW ANATOMY the axial skeleton, proximal humeri, and low signal-to-noise ratio.
proximal femora. With advancing age there Conventional intermediate weighted and T2
AND PHYSIOLOGY is further replacement of red marrow by weighted spin-echo sequences demonstrate
The bone marrow is the 5th largest organ of yellow marrow, with older individuals relatively low contrast between red marrow
the human body. Its chief function is commonly having a spine and pelvis and yellow marrow. In addition there is
hematopoietic, providing the optimal supply dominated by yellow marrow. Residual decreased sensitivity and conspicuousness
of circulating platelets, white and red blood islands of hematopoietic marrow can persist for the depiction of most types of bone
cells to meet the body´s requirements for in the long bones. The most common sites marrow pathology. These problems are
coagulation, immunity, and oxygenation. are the proximal and distal femora, and corrected by utilizing the very long TR and TE
The histology of normal bone marrow proximal humeri. This pattern should not be times of heavily T2 weighted fast spin-echo
consists of a number of components mistaken for pathology. Another common images used in conjunction with fat-
including: (1) an osseous component; (2) a normal variation in distribution of marrow is saturation. The sensitivity of this sequence
cellular component; (3) a supporting system. the presence of focal fatty marrow within the for detecting bone marrow pathology is
The osseous component consists of spine. The distal appendicular skeleton similar to that of STIR imaging. Several
cancellous bone composed of primary and usually has a uniform distribution of yellow practical advantages compared with STIR
secondary trabeculae. The cellular marrow in adults. include: (1) significantly decreased imaging
component includes hematopoietic, fat, and time; (2) improved signal-to-noise ratio. The
reticulum cells. The bone marrow supporting MR TECHNIQUE major disadvantage of T2 weighted fast
system consists of vascular, neural, and spin-echo with fat saturation is its
Pulse sequence selection determines the MR
lymphatic elements. dependence on excellent magnetic field
appearance of normal bone marrow as well
homogeneity for adequate fat suppression.
Hematopoietically active bone marrow is as the sensitivity and specificity for
Optimal results with fat saturation usually
referred to as hematopoietic marrow or red evaluating bone marrow disorders. A highly
require high-field strength systems, whereas
marrow. Red marrow contains approximately effective combination of pulse sequences for
STIR images can be obtained on low-or high
40% water, 40% fat, and 20% protein. the evaluation of bone marrow pathology
field strength systems.
Hematopoietically inactive marrow is includes: (1) T1 weighted spin-echo; and
referred to as yellow marrow or fatty marrow. either (2) fat-saturation T2 weighted fast The fast inversion recovery techniques
It contains approximately 15% water, 80% spin-echo; or (3) STIR / Fast STIR. significantly reduce the imaging time
fat, and 5% protein. These differences in required for STIR-like images. The role of
There is superb differentiation between red
chemical composition account for the these techniques in the evaluation of bone
and yellow bone marrow on T1 weighted
appearance of red and yellow marrow on marrow pathology is currently evolving.
spin-echo images. On T1 weighted images
various MRI pulse sequences. There is also a Recent studies suggest an emerging role for
the yellow marrow is hyperintense in signal
structural difference between red and yellow this pulse sequence for performing whole-
intensity as contrasted with the relatively
marrow. In particular, the vascular network body bone marrow MRI for the evaluation of
decreased signal intensity of red marrow.
of red marrow can be characterized as patients with suspected skeletal metastasis or
These differences in signal intensity are a
being rich, while that of yellow marrow is multiple myeloma.
direct reflection of the differences in
more sparse. fat/water content within red and yellow Opposed-phase GRE sequences with a long
At birth, red marrow is present throughout marrow. Specifically, increased fat content repitition time have recently been shown to
the entire skeleton. Epiphyses and within yellow marrow contributes to be sensitive for demonstrating red bone
apophyses are cartilaginous at birth, significant shortening of the T1 relaxation marrow pathology. This type of sequence
however, they later contain yellow marrow time compared with red marrow. Both results in low signal intensity of intact red
throughout life. Epiphyseal red marrow can benign and malignant disorders of bone bone marrow and high signal intensity
be a normal variant in adults, however, in marrow have long T1 values which result in positive contrast imaging of pathology.
the humeral head and femoral head. marrow signal intensity that is significantly
Normal physiological conversion of red-to- decreased. The signal intensity of these CLASSIFICATION OF BONE
yellow marrow occurs in a predictable and lesions on T1 weighted spin-echo images is
orderly fashion with completion by the age usually less than that of intervertebral discs
of 25 years when the adult pattern is in the spine and less than that of muscle in MRI is ideally suited for evaluation of both
reached. Conversion occurs first in the the extremities. diffuse and focal bone marrow disease. The
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MRI of Bone Marrow
bone marrow can be affected by a wide susceptibility “blooming“ of trabeculae. The should not be confused for more significant
variety of pathologic processes, such as finding of bone marrow edema is non- pathology.
myeloproliferative diseases, osteomyelitis, specific, and can be seen as a result of One of the most common clinical problems
and hemochromatosis, but metastatic trauma, infection, ischemia, reaction to is the distinction of benign osteoporotic
disease and multiple myeloma are the most adjacent neoplasia, or it may be idiopathic. compression fracture of the spine from
common causes of bone marrow disease. For example, the bone marrow edema seen pathologic compression fracture due to
Vogler et. al., have nicely grouped the bone on MR images of the hip may be secondary malignant processes. A vertebral body
marrow disease conditions according to to transient or migratory osteoporosis, early wedge compression fracture that
common pathophysiological patterns. osteonecrosis, or the bone marrow edema demonstrates complete preservation of
syndrome. normal bone marrow signal intensity is
Reconversion consistent with a chronic benign
The first group includes diseases where there
Marrow Ischemia compression fracture. Acute or subacute
benign vertebral body compression fractures
is an increased need for hematopoietic This category of bone marrow disease
demonstrate marrow signal alteration in a
marrow. Failure of conversion from red encompasses both avascular necrosis of
regular pattern with smooth margins.
marrow to yellow marrow occurs when the subchondral bone and medullary bone
Frequently this is in a band-like pattern
disorder develops in childhood. infarcts. Bone marrow ischemia favours fatty
paralleling the involved vertebral body end
Reconversion occurs when the adult bone marrow over hematopoietic marrow. This is
plate. An underlying fracture line is
marrow is stressed. Reconversion occurs in most likely due to the limited vascular supply
of yellow marrow relative to red marrow. frequently visible. The posterior height of the
the reverse order of normal conversion,
vertebral body is also frequently preserved.
progressing from proximal-to-distal. This is
The marrow signal returns to normal in one-
seen in entities such as anemia of chronic POTENTIAL PROBLEMS to-three months. Malignant vertebral body
illness, thalassemia, and sickle cell disease.
There are a number of potential problems compression fractures demonstrate
encountered in the interpretation of bone complete replacement of normal marrow
Marrow Infiltration marrow MR imaging. The most common signal intensity in 88% of cases. If
Marrow infiltration can be either focal or include recognition of normal variants. incomplete, it is generally in an irregular
diffuse and is most commonly due to These include: (1) residual islands of distribution. Focal metastasis elsewhere,
neoplastic disease. There is replacement of hematopoietic marrow, especially in the posterior element involvement, cortical
the normal fatty marrow cells by neoplasia proximal femora and humeri; (2) residual disruption, and a ballooned morphology of
or other pathologic tissue. Examples of red marrow within the proximal humeral the vertebral body favour a neoplastic
neoplastic disease include metastatic epiphysis and femoral capital epiphysis; (3) etiology. Neither the presence nor the
disease, lymphoma/leukemia, and multiple focal fatty marrow, especially within the absence of enhancement following
myeloma. Examples of non-neoplastic spine. intravenous gadolinium appears specific
disorders include eosinophilic granuloma, Other problems are purely technical in enough to preclude serial MRI or biopsy. The
Gaucher´s disease, and the nature. For example, there is a significant presence of a paraspinal mass can also be
mucopolysaccharidoses. decrease in sensitivity for bone marrow present with either a benign or malignant
pathology when intermediate weighted etiology.
Myeloid Depletion sequences are utilized in place of true T1 It should be noted that vertebral
weighted spin-echo images. Similar compression fractures in patients with
These disorders are characterized by
problems arise if fast spin-echo imaging is multiple myeloma can appear benign at MR
replacement of hematopoietic elements by
utilized without adequate fat saturation. imaging, and their distribution is similar to
fat cells. These processes include aplastic
Similarly, it is important to obtain pre- that observed in osteoporotic fractures. The
anemia, radiation therapy, and chemo-
contrast T1 weighted spin-echo images as possibility of multiple myeloma, therefore,
therapy. Following bone marrow
post-gadolinium images alone, without the should not be excluded in patients with
transplantation, a marrow “band“ pattern is
use of fat saturation, can cause yellow benign-appearing vertebral compression
seen reflecting repopulation of the bone
marrow to appear homogeneously high fractures at MR imaging.
marrow in the peripheral sinusoids of the
signal, completely obscuring lesions which
vertebral body. This finding consists of
are easily seen on pre-gadolinium images. References
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