Intra-Articular Contrast (MR arthrography)
In last month’s column, I briefly discussed the topic of the use of contrast in MRI and the concept of tissue enhancement. I specifically referred to intravenous contrast in that column. In this column, I will discuss the subject of intra-articular contrast, also referred to as MR arthrography.
What is arthrography? The original arthrogram studies that predated MRI utilized plain film x-ray after the injection of contrast material into a joint. This type of arthrogram suffers the same deficiencies when compared to MRI imaging, as does plain film x-ray in comparison to MRI. Specifically, I am referring to the lack of three-dimensional imaging and poor soft tissue visualization. Traditional arthrograms do provide some information that cannot be obtained from plain film x-ray alone because they allow a degree of visualization of the interior of the joint. However, visualization in this manner is indirect. The lining of the joint is, in effect, painted with the contrast thus making structures that were virtually invisible on x-ray suddenly visible. Actually, only the surfaces of the structures are visible.
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MRI imaging has eliminated much of the need for plain film arthrography, as the joint may be visualized directly and in three dimensions. MRI arthrography combines the inherent advantages of MRI with the supplemental benefit of arthrography. Intra-articular MRI contrast exams are not ordered as often as intravenous MRI contrast exams, however, they may be useful in specific instances.
The procedure for performing intra-articular contrast involves injecting a joint with a fluid mixture containing gadolinium. Gadolinium is also the contrast medium used in intravenous contrast. The fluid distends the joint capsule and insinuates itself in the various nooks and crannies within the joint. This fluid may also enter defects within intra-articular structures, such as fibrocartilage tears, which may be difficult to see on traditional MRI exams.
Contrast images are obtained with T1 weighted pulse sequences. Similar to the intravenous contrast exam, the intra-articular contrast appears as a high signal intensity on the T1 weighted images. Thus this high signal may be seen to extend into entities such as tears of fibrocartilage (which may be particularly difficult to see on non-contrast exams) or to extend outside of the joint capsule in cases of capsular disruption. In the case of an osteochondral fragment that may be seated well within the parent bone defect, the high signal contrast may be seen to surround the fragment with a thin line of contrast. This is useful in assessing the stability of the fragment.
In an effort to provide you with a wristband quick reference guide, below is a list of the possible indications for MR arthrography for some of the more commonly imaged joints in the body:
Shoulder: Glenoid labrum tears, capsular/ligamentous tears, partial thickness rotator cuff tears.
Elbow: Intra-articular loose bodies when there is no intra-articular effusion, capsular disruption, partial tears of the ulnar collateral ligament, assessment of the stability of osteochondral fragments.
Hip: Acetabular labrum tears.
Knee: To help differentiate post operative scar tissue from meniscal tear.
Ankle: Assessment of stability for talar dome osteochondral fractures, capsular disruption.
Intra-articular contrasts exams are not limited to the indications outlined above, but this will serve as a short list to help guide clinical decision making. At no time should these exams be performed without full consideration of the risks vs. benefits of the study. Some of the negative considerations that should be taken into account are as follows:
- It is an invasive procedure, and as such, the potential for infection is omnipresent. Although, precautions taken to avert this consequence are extensive and routine.
- The procedure is not comfortable. The joint is markedly extended by the injection of the contrast, and there are varying degrees of discomfort experienced by the patient.
- Lastly, the cost of an intra-articular contrast exam is significantly increased compared to the non-contrast exam. This is due to the additional cost of the gadolinium and the fees incurred by having a physician present to inject the contrast.
In conclusion, intra-articular contrast MRI studies are not routinely ordered, but given the appropriate circumstances, they can be extremely useful in answering specific clinical questions. As always, a quick consultation with the reading radiologist will often provide additional insight when deciding whether this type of exam is appropriate for a given patient.
