This paper will focus on the applications of musculoskeletal MRI of tumors, infection, and internal joint derangement and discuss the role of IV or intra-articular contrast in these settings.
is a third-year Radiology Resident at the University of Washington
Medical Center, Seattle, WA. He received his MD from the New York
University School of Medicine in 1998. Following his residency, he
will remain at the University of Washington to begin a
Musculoskeletal Imaging fellowship in 2003.
The evolution of magnetic resonance imaging (MRI) has
greatly influenced the clinical practice of musculoskeletal
imaging. The superb inherent soft-tissue contrast, spatial
resolution, and accurate depiction of both normal anatomic
structures and pathologic processes have revolutionized the
evaluation of many musculoskeletal disorders. The role of
noncontrast-enhanced MRI is well established in the evaluation
of many musculoskeletal disorders. The added utility of
intravenous (IV) or intra-articular gadolinium-based contrast
agents, however, is not always clear. This paper will focus on
the applications of musculoskeletal MRI of tumors, infection, and
internal joint derangement and discuss the role of IV or
intra-articular contrast in these settings.
Over the past 10 to 15 years, magnetic resonance imaging (MRI)
has had a major impact on musculoskeletal imaging. Excellent
soft-tissue contrast, spatial resolution, and multiplanar imaging
are among the major advantages of MRI. The majority of applications
for musculoskeletal MRI fall into one of three major categories of
disease: (1) tumors and tumor-like conditions; (2) infectious
processes; and (3) derangement within and about joints. Although
noncontrast-enhanced MRI is sufficient for the evaluation of many
musculoskeletal conditions, the addition of either intravenous (IV)
or intra-articular gadolinium-based contrast agents is, at times,
necessary to improve the evaluation of certain disease
Basic principles of gadolinium contrast agents in
Whether administered intravenously or intra-articularly,
gadolinium-based contrast agents cause T1 shortening, due to their
paramagnetic properties, which enhances relaxation rates of nearby
protons. When administered intravenously, gadolinium contrast
compounds, just as iodinated contrast agents, distribute rapidly
within the intravascular space, diffuse within the extracellular
space, and are excreted by the kidneys.
T1-weighted sequences depict areas of contrast-enhancement.
Contrast-enhanced T1-weighted sequences with chemical fat
suppression will increase the conspicuity of the area of contrast
enhancement and may help to differentiate regions of enhancement
from fatty tissue.
When administered intravenously, the standard dose of contrast
for musculoskeletal applications is 0.1 mmol/kg of body weight.
Standard static or dynamic images can be performed. Static
postcontrast images are obtained at a set time interval shortly
after IV contrast administration. Dynamic postcontrast imaging is
utilized primarily in evaluating neoplastic processes. Typically,
ultra-fast T1-weighted snapshot sequences are performed during the
first 3 minutes following bolus contrast injection. Images are
obtained at an optimal rate of one image per 3.5 to 7 seconds
through a preselected slice, which optimally represents the tumor.
Utilizing postprocessing software, signal intensity-to-time curves
can be obtained and analyzed. The multiple images obtained during
the period of contrast enhancement can also be viewed in a cine
MR arthrography is an emerging technique, utilized to evaluate
pathology in and about joints. MR arthrography can be performed
either directly or indirectly. In the direct technique, gadolinium
is injected directly into the joint space. A 20- or 22-gauge needle
is placed within the joint of interest (with or without
fluoroscopic guidance, depending on the joint). If using
fluoroscopic guidance, a small amount of iodinated contrast can be
injected to confirm needle position. Depending on the joint
involved, a variable amount of gadolinium-saline solution
(typically a 1:200 to 1:250 ratio of gadolinium to saline), with or
without lidocaine, is injected into the joint space. The joint can
then be imaged immediately following contrast injection, and
ideally within 30 to 45 minutes, to maximize distention of the
joint space and to minimize absorption of contrast from the joint
space. Typically, T1-weighted sequences with fat suppression and
T2-weighted sequences are utilized.
In contrast to direct MR arthrography, indirect MR arthrography
utilizes an IV injection of gadolinium. Following a delay of 5 to
20 minutes and exercise of the joint to optimize distribution of
gadolinium, the contrast will have diffused from the synovium into
the joint fluid.
Gadolinium contrast agents are relatively safe, with the most
common reactions reported to be headache, nausea, dizziness, and
injection-site symptoms. Serious reactions, such as death due to
anaphylaxis, are rare. The overall reaction rate, with a 0.1
mmol/kg dose, is reported to be 2.4%. The most frequent symptoms
included nausea (0.4%) and headache (0.4%).
No known reported deaths rates due to intravenous gadolinium-based
contrast agents have been published.
Although conventional radiographs remain the most reliable
predictor of tumor histology,
MRI can be a powerful tool in the evaluation of tumors of soft
tissue and bone. When determining the intra- or extracompartmental
extent of a tumor and its relationship to neighboring structures,
for example, MRI is the modality of choice.
The indications for IV gadolinium in augmenting the MRI evaluation
of tumors is not entirely clear, since a great deal of information
can be obtained from noncontrast-enhanced T1- and T2-weighted, as
well as other noncontrast-enhanced sequences. Studies have shown
that contrast adds further significant information in only ¾ 10% of
Noncontrast-enhanced MRI scans can characterize most lesions
accurately, including lipoma, nerve sheath tumor, pigmented
villonodular synovitis, and many sarcomas.
This section will review the broad categories of tumor evaluation
and how they might benefit from the IV administration of
gadolinium. These categories include local staging/biopsy planning,
tissue characterization, evaluating response to chemotherapy, and
Local staging/biopsy planning
Evaluating the local extent of a tumor is the most important
role for MRI in tumor evaluation.
Bone, joint, muscle, and neurovascular involvement must all be
defined accurately before biopsy can be performed and subsequent
therapy planned. Unenhanced MRI is generally quite good at
delineating the relationship between these structures and the tumor
(figure 1). Most tumors have low signal on T1-weighted sequences,
which are best for evaluating marrow involvement. Generally, tumors
and peritumoral edema have high signal on T2-weighted images, and
thus are readily distinguishable from adjacent muscle or bone.
However, the use of contrast can assist in determining the extent
of tumor versus non-neoplastic peritumoral edema.
Accurate delineation of tumor margins may be helpful in surgical
planning, particularly when limb-sparing surgery is contemplated.
One area in which gadolinium appears to be of particular value
is in assisting in biopsy. This may be especially important in
bulky tumors with large areas of necrosis. Biopsy can thus be
targeted to the solid, enhancing tissue, which is presumed to be
Contrast-enhanced MRI is limited in its ability to distinguish
benign from malignant tumors.
Malignant tumors are thought to possess a greater degree of
enhancement, as well as more rapid uptake of contrast.
Static and dynamic postcontrast imaging have been studied, but
despite these techniques, there is a high degree of overlap between
the appearance of many malignant and benign tumors. In fact, the
correct histological diagnosis can be made in only 25% to 30% of
lesions, when based on MRI alone.
Rim-to-center differential enhancement ratios have been proposed as
a method for histologic evaluation,
but more research needs to be performed in this area before MRI can
be used to distinguish benign from malignant tumors accurately.
Although contrast-enhanced MRI may not be optimal for
distinguishing benign from malignant tumor, it can assist in
determining several other potentially important tissue
Contrast-enhanced MRI can be used to differentiate solid from
cystic lesions, especially when signal characteristics on
noncontrast-enhanced sequences do not clearly make this
distinction. Cystic or partially cystic lesions are identified
readily due to their lack of internal enhancement.
Patterns of rim enhancement (thin versus thick), as well as
enhancing internal septations, also assist in diagnosis. Benign and
malignant lesions that may appear cystic on noncontrast-enhanced
sequences include synovial or ganglion cyst, lymphocele, seroma,
abscess, bursitis, chondrosarcoma, myxoid lesions (benign and
malignant), sarcomas, and metastases.
Administration of gadolinium may help in differentiating these
entities, when the diagnosis is not clear on noncontrast-enhanced
Another application for utilizing contrast is in the evaluation
of hematomas. In rare circumstances, sarcomas may present within
muscle hematoma. Administration of gadolinium will reveal small
enhancing foci of tumor, which would go undetected on
noncontrast-enhanced imaging. The only caveat is that
fibrovascular tissue in organizing hematomas may show enhancement.
Response to chemotherapy
The initial response to chemotherapy is an important predictor
in determining eventual treatment outcome. Treatment protocols
(including chemotherapy regimens, surgery timing, and radiation
therapy) are often influenced by determination of the initial
response to therapy.
Unfortunately, conventional radiographs, computed tomography (CT),
radionuclide studies, and static contrast-enhanced MRI have not
been shown to be effective in measuring response to initial
chemotherapy. Several studies have shown that dynamic
contrast-enhanced MRI is a promising technique in measuring initial
tumor response to therapy.
As described earlier, tumor enhancement curves with respect to time
are obtained following bolus administration of contrast, using fast
low-angle shot (FLASH) sequences. Curves are obtained both before
and during initial chemotherapy. Responders will show a decrease in
the slope of the curve following treatment.
The limitations are that dynamic contrast MRI is not widely
available, it is time-consuming, and is not yet completely
Detecting tumor recurrence
MRI is extremely useful in the follow-up of patients following
treatment for bone tumors. Low signal on both T1- and T2-weighted
sequences in the previous site of tumor is a good indicator of no
tumor recurrence. In certain instances, high T2 signal regions may
persist within the post-treatment site. The appearance, however, is
nonspecific and may represent necrosis, edema, hemorrhage,
granulation tissue, or recurrent edema.
Static postcontrast images may be helpful in this instance, but
reactive tissue and residual tumor may both enhance to a similar
degree on the static postcontrast images. Dynamic contrast-enhanced
MRI may play a role in these situations.
Tumors will enhance quickly, whereas reactive tissue will enhance
Musculoskeletal infections, including cellulitis, fasciitis
(including necrotizing fasciitis), myositis/pyomyositis, septic
arthritis, septic tenosynovitis, and osteomyelitis, may affect a
variety of structures, including skin, fascia, muscle, joints,
tendon sheaths, and bone.
Such infections are usually detected clinically with symptoms that
include local or diffuse swelling, erythema, pain, and fever.
Laboratory tests, including erythrocyte sedimentation rate, white
blood cell count, and blood cultures, can help confirm the
The most common pathogens include
. When the skin is disrupted due to trauma, surgery, or vascular
compromise, the risk of osteomyelitis is greater. Imaging is
usually obtained when osseous infection is suspected, in complex
soft-tissue infections, or if response to antibiotic therapy is
The initial imaging of osteomyelitis typically consists of
conventional radiographs; however, this method is insensitive and
may take up to 10 days to reveal an abnormality. Radionuclide
studies can be helpful, but are often nonspecific, and cannot
differentiate neoplasm, infection, and trauma reliably.
Noncontrast-enhanced MRI is a cost-effective, sensitive, and
specific study for detecting osteomyelitis (figure 2). The reported
rates of sensitivity and specificity for MR detection of
osteomyelitis range from 86% to 98% and 77% to 100%, respectively.
Standard sequences may include a combination of T1-weighted,
T2-weighted, and/or short tau inversion recovery (STIR) or
T2-weighted sequences with chemical fat suppression. T1-weighted
images are generally best for evaluating marrow infection.
T1-weighted sequences will show infection as intermediate or low
signal within the bone marrow. Infection is high in signal on
T2-weighted and STIR images.
Chronic and acute osteomyelitis can be distinguished, as well.
Acute disease causes poor definition of soft-tissue planes, lack of
cortical thickening, and indistinct transition between normal and
abnormal bone marrow. Chronic osteomyelitis will show cortical
thickening and a more readily defined distinction between the
normal and abnormal tissues.
In both osteomyelitis and soft-tissue infections, MRI can depict
the extent of infection accurately. Determining the presence of
necrotic tissue or abscess is also important in treatment planning.
Necrotic tissue is treated surgically, whereas viable tissue is
treated with antibiotics. The addition of IV contrast will readily
demonstrate areas of necrosis or abscess (figure 3). Distinguishing
viable from necrotic tissue will also aid in biopsy or fine-needle
aspiration for culture. If surgery is contemplated, the excellent
spatial resolution of MRI will aid in surgical planning.
MRI is also very sensitive for detection of septic arthritis.
Very small joint effusions are detected readily. The addition of
contrast may reveal enhancement and hypertrophy of the synovium.
These findings may also be seen in transient synovitis, but the
presence of adjacent signal abnormality within the bone is more
specific for septic arthritis.
Evaluation of internal joint derangement
MRI evaluation of the bones and soft tissues around the joints
has been a major advance in musculoskeletal imaging. The normal
anatomy, as well as pathology of joints, can be evaluated in
exquisite detail. The role of noncontrast-enhanced MRI in imaging
suspected joint injuries is well established. MRI will often
confirm clinically suspected injuries such as meniscal tears and
ligament or tendon injuries (figure 4).
It can also uncover unsuspected pathology, which may either guide
arthroscopy or would have been difficult to detect with
Recent studies in the orthopedic literature on the impact of
shoulder MRI on clinical decision making showed that MR evaluation
made statistically significant changes in clinical management.
When gadolinium is used in the evaluation of joint injury, it is
primarily used for direct MR arthrography. Direct MR arthrography
with gadolinium is an emerging technique that relies on the
improved visualization of the articular structures when
intra-articular fluid is present. Distention of the joint space by
the intra-articular injection of gadolinium is a key contributor to
the improved assessment of complex intra-articular structures.
A detailed discussion of all current indications for direct MR
arthrography is beyond the scope of this paper; however, some
situations where it is advantageous over conventional MRI include
the evaluation of labral abnormalities of the hip, osteochondral
injuries, intra-articular loose bodies, postoperative evaluation of
the knee after meniscal repair, characterization of ankle/elbow
ligament injuries, and evaluation of glenohumeral joint instability
The most common studies performed are for evaluation of shoulder
joint instability and the postoperative knee.
Drawbacks of direct MR arthrography, aside from patient
discomfort, include that it is invasive and time-consuming and has
the potential for complications. Morbidity with MR arthrography,
however, appears to be low, with one study reporting an adverse
reaction rate of 3.6%.
The most common side effects included pain, vasovagal reaction, and
Another recent study found that the majority of patients undergoing
the procedure found it acceptable, in that they were willing to
undergo pain, anxiety, and potential complications in order to
achieve a potentially more accurate diagnosis.
Indirect MR arthrography is an alternative to the direct method.
Indirect arthrography involves IV injection of contrast and imaging
the joint after a 5- to 20-minute delay, as described earlier.
Following the delay, the joint fluid will enhance, creating an
Advantages of this technique over direct MR arthrography are that
it is less invasive and less time-consuming to perform. However,
one major disadvantage is that if no native effusion is present,
the diagnostic advantage of a distended joint space is not present,
as it is in direct MR arthrography.
Studies comparing the efficacy of indirect MR arthrography to
conventional MRI and direct MR arthrography are ongoing.
Preliminary studies suggest that indirect MR arthrography may be
superior to non-contrast MRI in detecting similar types of
pathology that are more readily detected with direct MR
However, further studies need to be performed in order to more
clearly define the role of indirect MR arthropathy and in which
circumstances it may be an acceptable alternative to direct MR
MRI is well established as an important tool in evaluating a
variety of musculoskeletal disorders. Conventional
noncontrast-enhanced MRI provides an excellent means of evaluating
the above-mentioned major musculoskeletal disease categories, as
well as potentially many others. The role of the use of gadolinium
contrast agents is under ongoing investigation. However, there are
numerous situations in which its use is beneficial. In tumor
imaging, the routine use of gadolinium is not necessarily
warranted, but it can assist in biopsy planning and more accurate
delineation of tumor margins. Dynamic contrast-enhanced MRI has
potential roles in gauging tumor response and recurrence. The
routine diagnosis of osteomyelitis does not require administration
of gadolinium. Imaging of more complicated osseous and soft-tissue
infections, especially where infection extent and necrosis are of
concern, will benefit from IV contrast. Finally, in the evaluation
of suspected articular injuries or postoperative joints, MR
arthrography is an emerging technique, which is superior to
noncontrast-enhanced MRI in certain clinical scenarios.
The author would like to thank Dr. Eva M. Escobedo for reviewing
the manuscript, as well as Drs. John C. Hunter and Ranjeet Singh
for their assistance in obtaining images.