Magnetic resonance imaging of the wrist in rheumatoid arthritis

Despite the extraordinary advances made in medical imaging over the past two decades and the central role that magnetic resonance imaging (MRI) and other sophisticated technologies now play in routine clinical practice, rheumatology has benefited relatively little from these advances thus far. Over the past few years, however, evidence has accumulated to show that MRI can identify joint damage in patients with rheumatoid arthritis earlier and more sensitively than other techniques can, and that MRI can directly visualize and monitor changes in synovium and bone that precede actual bone erosion. Much of this development is being driven by the pharmaceutical and biotechnology industries as they search for novel therapies to combat this disease. Accordingly, the imaging tools that ultimately will be used to direct patients to specific therapies and then to monitor treatment effectiveness and safety are currently being refined and validated in rigorous multicenter and multinational clinical trials aimed at gaining regulatory approval of these new therapies. As these therapies become available for clinical use, radiologists can anticipate increased demand for expertise and experience in evaluating disease progression and treatment response with these techniques and the emergence of MRI systems specifically adapted for this application. The following discussion reviews the current status of this development, and points to areas where further advances are anticipated in the near future.

Magnetic resonance imaging of rheumatoid arthritis: the evolution of clinical applications through clinical trials

Powerful techniques are being developed for evaluating rheumatoid arthritis with magnetic resonance imaging (MRI). Much of this development is being driven by the pharmaceutical and biotechnology industries searching for novel therapies for this disease. Accordingly, the imaging tools that ultimately will be used to direct patients to specific therapies and then to monitor treatment effectiveness and safety are currently being refined and validated in rigorous multicenter and multinational clinical trials aimed at gaining regulatory approval of these new therapies. As these trials approach completion, rheumatologists can anticipate an increased demand for expertise and experience in evaluating disease progression and treatment response with these techniques and the emergence of MRI systems specifically designed for this market. The following discussion reviews this novel pathway for evolving imaging techniques for clinical use through clinical drug trials, lists the most promising MRI markers available today for evaluating joint destruction in rheumatoid arthritis, and speculates on how these techniques will find their way into clinical practice.

Magnetic resonance imaging in rheumatoid arthritis: current status and future directions

The performance of alternative imaging endpoints in clinical trials can be compared in terms of validity, rate of change, measurement precision, and convenience and cost. With respect to technical performance, magnetic resonance imaging (MRI) appears to show greater sensitivity than radiography for detecting bone abnormalities in rheumatoid arthritis (RA). In addition to monitoring changes in the bones, cartilage, and synovium, MRI can directly visualize the full spectrum of tendon pathology, and has been shown to identify tendonitis and tendon rupture with greater accuracy than clinical examination. MRI is currently regarded to be the most sensitive imaging technique for identifying trauma, infection, ischemia, and primary and secondary neoplasia of bone. Several studies have also shown MRI to be highly sensitive for detecting what appear to be bone erosions in the hands and wrists of patients with RA. MRI shows remarkable promise as a tool for identifying and monitoring structural damage in the joints of patients with RA. MRI appears to be able to identify bone erosions with greater sensitivity than radiography, and to disclose edema-like changes in the marrow, which may precede actual erosion formation. As new therapies with structure modifying capabilities enter the clinic, the ability to identify patients appropriate for those therapies and then to monitor the effectiveness and safety of treatment become increasingly important.

Automated measurement of radiographic hip joint-space width

Radiographic joint-space narrowing (JSN) is the principle indicator of cartilage loss in osteoarthritis (OA). JSN is usually assessed qualitatively by visual inspection or in clinical research, is measured manually with a graduated handheld lens directly applied to the x-ray film, or from digitized radiographs by hand tracing the joint margins with a mouse. The minimum joint-space width (mJSW) and joint-space area (JSA) are recorded as the indices of OA progression in epidemiological studies and clinical drug trials. We present a computerized method that automatically finds the articular margins of the hip to improve determination of mJSW and JSA. The algorithm requires that three seed points are manually identified on the femoral head and uses three steps to process each digitized hip x-ray. First, a Hough transform finds the center and radius (R) of a circle that approximates the femoral head. Finding R indicates whether magnification differences must be corrected on repeat exams. Second, a gradient algorithm finds the edge of the femoral head and acetabulum. Third, the mid-line of the femoral neck is automatically found and used to define the joint portion (theta) that is assessed for narrowing. theta is fixed for follow-up exams of the same subject. The algorithm was evaluated in three ways to determine its performance characteristics. First, the inter-reader and intra-reader variability for mJSW and JSA associated with the selection of the seed points was found to be negligible (< 1%) compared to the variability associated with manual scoring with a lens or by tracing the joint margins with a mouse. Second, from duplicate hip x-rays of 19 subjects with OA, the Root Mean Square Standard Deviation and coefficient of variation for mJSW and JSA defined by the algorithm was determined to be better than manual techniques by at least a factor of 2. Third, the algorithm correctly identified the joint margin in more than 85% of the 105 cases tested. Automated measures of radiographic hip joint-space narrowing is less subjective than manual methods and may be applicable for monitoring OA progression in clinical research.

Scratching the surface: articular cartilage disorders in the knee

Powerful techniques with MR imaging are being developed for evaluating articular cartilage. Pharmaceutical and biotechnology development is driven largely by the search for novel therapeutic solutions to the growing problem of arthritis in our aging society. Accordingly, imaging tools that will be used to direct patients to specific therapies and then to monitor treatment effectiveness and safety presently are being refined and validated in rigorous multicenter and multinational clinical trials aimed at gaining regulatory approval. As trials approach completion, radiologists can anticipate an increased demand for expertise and experience in evaluating articular cartilage disorders. This article reviews this novel mechanism for evolving imaging techniques for clinical use through clinical drug trials, lists the most promising MR imaging markers available for evaluating cartilage integrity, and speculates on how these techniques will find their way into clinical practice.

Trainable rule-based algorithm for the measurement of joint space width in digital radiographic images of the knee

The progression of osteoarthritis (OA) can be monitored by measuring the minimum joint space width (mJSW) between the edges of the femoral condyle and the tibial plateau on radiographs of the knee. This is generally performed by a trained physician using a graduated magnifying lens and is prone to the subjectivity and variation associated with observer measurement. We have developed software that performs this measurement automatically on digitized radiographs. The test data consisted of 180 digitized radiographs of the knee (90 duplicate acquisitions) from 18 normal (nonarthritic) subjects and 38 images from 10 subjects with OA. These were digitized and manually cropped so that the images were free of nonanatomical structures and the knee was approximately centered. The software first determined the edge of the femoral condyle on 400 microm pixel subsampled images. Contours marking the location of the tibial plateau in the medial compartment were found on 100 microm images using the femoral edge as a reference. The algorithm was trained using an independent but similar data set and using a jackknife approach with the test data. The results were compared to contours drawn by a trained reader and the duplicate acquisitions were used to measure the reproducibility of the mJSW measurement. The reproducibility was 0.16 mm and 0.18 mm for normal and osteoarthritic knees, respectively, representing an improvement of approximately a factor of 2 over manual measurement. The algorithm also showed excellent agreement with the hand-drawn contours and with mJSW determined by the manual method.

Accuracy of T2-weighted fast spin-echo MR imaging with fat saturation in detecting cartilage defects in the knee: comparison with arthroscopy in 130 patients

OBJECTIVE

The purpose of this study was to assess the accuracy of routine T2-weighted MR imaging in detecting and grading articular cartilage lesions in the knee compared with arthroscopy.

SUBJECTS AND METHODS

We examined 130 consecutive patients who underwent MR imaging and arthroscopy of the knee for suspected internal derangement. MR imaging consisted of axial and coronal T2-weighted fast spin-echo sequences with fat saturation and sagittal T2-weighted spin-echo sequences. Each single plane was evaluated and graded for the presence and appearance of articular cartilage defects using a standard arthroscopic grading scheme adapted to MR imaging.

RESULTS

Of the 86 arthroscopically proven abnormalities, 81 were detected on MR imaging. Sensitivity of the T2-weighted fast spin-echo sequence with fat saturation was 61% for the coronal plane alone and 59% for the axial plane alone. Specificity for each plane was 99%. Sensitivity for the sagittal T2-weighted spin-echo sequence was 40%, and specificity was 100%. Sensitivity of the combination of axial and coronal T2-weighted fast spin-echo sequences with fat saturation and sagittal T2-weighted spin-echo sequence compared with arthroscopy for revealing cartilage lesions was 94%, specificity was 99%, and accuracy was 98%. Sensitivity of coronal and axial T2-weighted fast spin-echo sequences with fat saturation was 93%, and specificity was 99%. Fifty-five lesions (64%) were identically graded on MR imaging and arthroscopy. Seventy-eight lesions (90%) were within one grade using MR imaging and arthroscopy, and 84 lesions (97%) were within two grades using MR imaging and arthroscopy.

CONCLUSION

T2-weighted fast spin-echo MR imaging with fat saturation is an accurate and fast technique for detecting and grading articular cartilage defects in the knee. The combination of the axial and coronal planes offers sufficient coverage of articular surfaces to provide a high sensitivity and specificity for chondral defects.

MR imaging of the arthritic rabbit knee joint using albumin-(Gd-DTPA)30 with correlation to histopathology

The purpose of this study was to demonstrate a technique, in a pilot study, for measuring abnormal capillary permeability in synovial tissue of rabbit arthritic knees using dynamic MRI with a gadolinium-based blood pool agent. Arthritis, simulating rheumatoid arthritis, was induced in knees of 8 rabbits by intra-articular injection of carrageenan (n = 4) or ovalbumin (n = 4). Sequential fat presaturated T1-weighted Spoiled Grass images were obtained before and up to 30 min after intravenous administration of albumin-(Gd-DTPA)30. Estimates of synovial tissue plasma-volume (PV), fractional-leak-rate (FLR), and permeability-surface-area-product (PS) were computed. Histologic correlation was obtained in the corresponding regions. Dynamic MRI showed extravasation of albumin-(Gd-DTPA)30 into hypertrophic synovium in six of the eight arthritic knees. Histologic examination of these six knees showed markedly inflamed synovium. The two knees that did not show abnormal vascular permeability contained non-hypertrophic synovium. None of the rabbits showed abnormal permeability in muscle. MRI derived microvascular characteristics (PV, FLR and PS) correlated positively (r2 = 0.51, 0.97 and 0.86) with the histology. Factors involving the structural and functional microvascular characteristics of synovial tissue can be estimated non-invasively using albumin-(Gd-DTPA)30. This technique may be useful for monitoring disease progression and treatment response in rheumatoid arthritis.

Arthritic temporomandibular joint: correlation of macromolecular contrast-enhanced MR imaging parameters and histopathologic findings

PURPOSE

To assess the utility of macromolecular contrast material-enhanced magnetic resonance (MR) imaging parameters for determining the histopathologic severity of temporomandibular joint (TMJ) arthritis.

MATERIALS AND METHODS

Ovalbumin was used to induce arthritis in the TMJs of 10 previously sensitized adult white rabbits. Five rabbits composed the sham-treated control group. Dynamic spin-echo imaging was performed immediately before and for 30 minutes after injection of macromolecular contrast medium. Histologic specimens of TMJ were assessed quantitatively for arthritis. Changes in MR signal intensity were derived from the synovial and subsynovial tissues of the TMJ, and plasma volume (PV) and permeability surface area product (PS) were calculated. These MR parameters and the arthritic scores were compared between sham-treated and antigen-challenged TMJs. The relationships between MR parameters and histopathologic indexes were also determined.

RESULTS

Arthritic TMJs showed marked enhancement of the synovial and subsynovial tissues over the imaging period. PS and all histopathologic indexes of arthritis were significantly greater (P < .005) in antigen-challenged than in sham-treated TMJs. PS demonstrated strong positive relationships with all histologic parameters of arthritis, indicating its utility for assessing the severity of joint inflammation.

CONCLUSION

Macromolecular contrast-enhanced MR imaging enables quantification of PS and PV in inflamed joints. This technique may provide insights into the pathogenesis of joint inflammation and noninvasive monitoring of disease severity and treatment response in arthritis.

Dedicated extremity MR imaging. An emerging technology

Dedicated extremity MR imaging represents a radical departure from conventional whole-body scanning. Extremity MR imaging offers such advantages as reduced cost, more convenient and inexpensive setting, greater patient comfort and safety, and high diagnostic power. This article examines some of the features of extremity MR imaging and how this technology is affecting musculoskeletal imaging in today's environment of cost containment and health care reform.

Mapping abnormal synovial vascular permeability in temporomandibular joint arthritis in the rabbit using MRI

An automated method for two-dimensional spatial depiction (mapping) of quantitative physiological tissue characteristics derived from contrast-enhanced MRI was applied to a model of inflammatory disease represented by antigen-induced arthritis of the temporomandibular joint in the rabbit. Specifically, an established two-compartment kinetic model of unidirectional mass transport was implemented on a pixel-by-pixel basis to generate maps of tissue permeability surface area product (PS) and fractional blood volume (BV) based on dynamic MRI intensity data after administration of albumin-(Gd-DTPA)30, a prototype macromolecular contrast medium designed for blood pool enhancement. Maps of PS and BV in a disease model of induced arthritis clearly depicted zones of increased permeability (up to approximately 200 microliters/cc/h-compared to 25 microliters/cc/h in normal tissues).

Magnetic resonance imaging of labral cysts of the hip

OBJECTIVE

To present the magnetic resonance (MR) imaging findings in patients with labral cysts adjacent to the acetabulum and to examine their association with hip pathology.

DESIGN

MR images and conventional radiographs of seven patients with paralabral cysts were retrospectively reviewed by three musculoskeletal radiologists.

PATIENTS

The patients included three men and four women with hip pain, ranging in age from 29 to 82 years. Two patients had developmental dysplasia of the hip and six had a history of remote trauma/dislocation. Clinical history and follow-up were obtained in all patients. Surgery was performed on one patient.

RESULTS AND CONCLUSIONS

Paralabral cysts were located in the posterosuperior aspect of the hip joint in five patients and in the anterior aspect in two patients. A tear of the adjacent acetabular labrum was confirmed surgically in one patient, and in all patients the MR features suggested the presence of an abnormal labrum. Osteoarthritis was observed in three patients and there was associated subchondral cyst formation in the acetabulum adjacent to the cyst in three patients. The paralabral cyst of the hip is well visualized on MR imaging and is seen in patients with a predisposition to labral pathology.

MR imaging

MRI is a tool of unprecedented capabilities for evaluating arthritis and its progression. Not only can it non-invasively delineate the anatomy of all components of a joint with unparalleled clarity, MRI is also capable of probing important functional and compositional parameters of disease in these tissues. Particularly intriguing is MRI's potential for identifying very early changes of joint disease when clinical symptoms may be minimal or absent. Early detection of patients who are at risk for developing progressive disease may allow appropriate treatment to be initiated earlier, when there may be a greater chance of favourable outcome. MRI can, furthermore, provide objective and quantitative measures of disease progression and treatment response. Certain parameters, such as articular cartilage volume, have been validated cross-sectionally; however, their longitudinal performance has yet to be established. Further work is, therefore, necessary to thoroughly validate and optimize some of these measures so that they can begin to be used in more powerful ways to explore the pathophysiology and potential therapies of arthritic disorders.

Indirect MR arthrography: optimization and clinical applications

PURPOSE

To evaluate and optimize a method for producing magnetic resonance (MR) images similar to MR arthrograms of multiple synovial joints with intravenous gadopentetate dimeglumine injection.

MATERIALS AND METHODS

The authors examined the effects of joint motion, dose of gadopentetate dimeglumine (0.1, 0.2, and 0.4 mmol/kg), and fat saturation on the enhancement rate of the joint cavity and the degree of image contrast generated among articular structures on MR images in 14 healthy volunteers. Shoulder, elbow, wrist, hip, knee, and ankle joints of 10 volunteers were imaged with optimized parameters. Indirect MR arthrographic findings in 17 patients with joint disorders (eg, rotator-cuff tears, meniscal tears, and osteoarthritis) were compared with arthroscopic findings.

RESULTS

Fat-saturated images obtained after 10 minutes of exercise and administration of 0.1 mmol/kg gadopentetate dimeglumine were similar to those obtained after intraarticular injection of contrast medium. Exercising the joint yielded the strongest joint-cavity enhancement. Increasing the dose of contrast medium in the unexercised joint did not statistically significantly improve the contrast-to-noise ratio. Rotator cuff tears, meniscal tears, and cartilage defects were better delineated with this method than with unenhanced MR imaging and showed good correlation with arthroscopic results.

CONCLUSION

Indirect MR arthrography of an exercised joint provides homogeneous enhancement and improved delineation of soft-tissue structures.

Emerging applications of magnetic resonance imaging in the evaluation of articular cartilage

MR imaging rapidly is emerging as a tool of unparalleled power for examining the articular cartilage and other important structures in diarthrodial joints. In addition to delineating the morphology of cartilage, MR imaging is capable of quantifying a variety of compositional and functional parameters relevant to arthritis. Moreover, because MR imaging is a nondestructive technique, multiple parameters can be analyzed in the same region of tissue and frequent serial examinations can be performed on even asymptomatic patients. This offers an unprecedented opportunity to study arthritis in ways not imaginable before and potentially to expand the envelope of MR imaging to include a population of patients for whom imaging has had relatively little to offer.

Tibial shaft fractures: assessment of fracture healing with computed tomography

OBJECTIVE

To assess the capability of CT in assessing stability of tibial shaft fractures with planimetry.

MATERIALS AND METHODS

Eighteen patients with fracture of the tibial shaft were treated by external fixator. All patients underwent CT 1, 6, 12, and 18 weeks postoperatively to assess the fracture healing. The callus formation and compacta were determined with planimetry. Fractometry, a noninvasive method to measure stability, was used as the gold standard to determine the stability of the fracture.

RESULTS

The patients were divided into three groups according to different periods of time for removal of external fixation. Twelve patients with stable fractures showed a steady increase of callus, which was 50% higher after 12 weeks. Three patients with delayed fracture healing demonstrated an increase of callus of > 50% after 18 weeks. Three patients with unstable fractures obtained only callus formation of < 20% after 15-18 weeks. The external fixator was removed and endomedullary nails were used for stabilization.

CONCLUSION

The CT data allow quantification of callus and compacta formation and are able to determine the stability of tibial shaft fractures.

Lipoma arborescens of the shoulder: magnetic resonance imaging findings

Lipoma arborescens is a rare intra-articular lesion that typically affects the knee. This condition represents villous lipomatous proliferation of the synovial membrane. The magnetic resonance imaging findings are diagnostic and include a frond-like, fatty synovial mass and associated joint effusion. The authors describe a 90-year-old woman with lipoma arborescens of the shoulder. To the authors' knowledge, lipoma arborescens has not previously been reported in this joint.

Quantification of the volume of articular cartilage in the metacarpophalangeal joints of the hand: accuracy and precision of three-dimensional MR imaging

OBJECTIVE

Cartilage loss is central to the development of joint failure in arthritis. However, radiographic assessment of cartilage loss is highly unreliable. This study examined the accuracy and reproducibility of a noninvasive technique for quantifying the volume of articular cartilage in the metacarpophalangeal joints of the hand by use of three-dimensional (3D) MR imaging.

SUBJECTS AND METHODS

Eight metacarpophalangeal joints (four normal, one rheumatoid arthritic, and three normal cadaveric) each were imaged three times with a 1.5-T clinical MR imaging scanner with a small partial volume coil and a fat-saturated 3D spoiled gradient-echo sequence optimized for delineating articular cartilage. The volumes of cartilage over the metacarpal and phalangeal surfaces were quantified by summing the voxels within segmented 3D reconstructions of the images. Cartilage volumes in the three cadaver joints also were estimated by scraping cartilage off the articular surfaces and measuring water displacement in graduated cylinders. These values were used as the gold standard for assessing the accuracy of cartilage volume quantification by MR imaging.

RESULTS

The fat-saturated sequence discriminated the articular cartilage from adjacent joint structures with high contrast and high spatial resolution. Cartilage volumes determined by MR imaging for the different subjects ranged from 115 microliters to 222 microliters for metacarpal cartilage and from 34 microliters to 86 microliters for proximal phalangeal cartilage. Accuracy errors for quantifying cartilage volume by MR imaging were -1.8% (95% confidence interval, -3.5% to -0.7%) for metacarpal cartilage and 9.1% (4.3% to 14.7%) for proximal phalangeal cartilage. Reproducibility errors were 5.2% (95% confidence interval, 2.9% to 7.6%) and 9.9% (5.4% to 15.1%), respectively.

CONCLUSION

Fat-suppressed T1-weighted 3D MR imaging provides sufficient contrast and spatial resolution to allow accurate and reproducible quantification of articular cartilage volume in the metacarpophalangeal joints of the hand. This technique may be useful for monitoring cartilage loss in patients with arthritis.

Soft tissue coccidioidomycosis on MRI

OBJECTIVE

To determine the appearance of soft tissue coccidioidomycosis on MRI.

MATERIALS AND METHODS

Two cases of soft coccidioidomycosis with preoperative MR imaging are presented.

RESULTS

Prospectively, infection was considered unlikely both clinically and on imaging studies. In retrospect, the MR appearance was nonspecific in one case and suggestive of infection in the other.

CONCLUSION

Radiologists should be prepared to entertain coccidioidal abscess as a differential consideration when soft tissue masses are seen on MRI, even when infection is not suggested clinically.

Posterosuperior glenoid impingement of the shoulder: findings at MR imaging and MR arthrography with arthroscopic correlation

PURPOSE

To determine the utility of magnetic resonance (MR) imaging and MR arthrography in the evaluation of arthroscopic findings of posterosuperior glenoid impingement.

MATERIALS AND METHODS

The findings at MR imaging, MR arthrography, and physical examination with the patient under anesthesia were retrospectively reviewed in eight patients with arthroscopic evidence of posterosuperior glenoid impingement.

RESULTS

All patients had shoulder pain; anterior instability was found in six patients. Other than bone marrow abnormalities, findings at MR imaging were not reliable for the detection of posterosuperior glenoid impingement. MR arthrography was superior to routine MR imaging in all four cases in which it was done; positioning the shoulder in abduction and external rotation was beneficial in three of four patients.

CONCLUSION

Impingement of the rotator cuff on the posterior superior glenoid labrum is a cause of posterior shoulder pain in athletes who throw. MR arthrography may allow detection of abnormalities associated with this clinical entity.

MR arthrographic depiction of tears of the rotator cuff: benefit of abduction and external rotation of the arm

PURPOSE

To show the effectiveness of positioning the arm in abduction and external rotation (ABER) during magnetic resonance (MR) arthrography for depiction of tears of the rotator cuff.

MATERIALS AND METHODS

Five throwing athletes with shoulder pain were prospectively imaged with standard MR imaging, MR arthrography, and ABER MR arthrography. The status of the rotator cuff was recorded; arthroscopic correlation was obtained.

RESULTS

One partial tear of the distal infraspinatus tendon was detected with ABER MR arthrography only. One full-thickness tear was detected with both MR arthrography and ABER MR arthrography, but the component of the tear that extended into the infraspinatus tendon was depicted with ABER MR arthrography only. One partial tear was detected with both MR arthrography and ABER MR arthrography; no additional information was provided by either technique alone.

CONCLUSION

The ABER position may be useful in detection and characterization of tears of the rotator cuff, especially partial tears of the undersurface. This information would be useful in selection of patients for conservative therapy, arthroscopy, or arthrotomy.

Quantification of articular cartilage in the knee with pulsed saturation transfer subtraction and fat-suppressed MR imaging: optimization and validation

PURPOSE

To assess the reproducibility and accuracy of volumetric quantifications of articular cartilage in the knee determined with three-dimensional (3D) magnetic resonance (MR) imaging combined with pulsed saturation transfer subtraction (STS) or T1-weighted fat suppression (FS) imaging.

MATERIALS AND METHODS

Eight osteoarthritic knees were imaged repeatedly with optimized STS and FS sequences. Cartilage volumes were determined from 3D reconstructions of FS and STS images and by means of water displacement of surgically retrieved tissue.

RESULTS

Mean over- or underestimation of cartilage volume at STS and FS imaging was 0.40 mL +/- 0.11 (standard deviation) (8.2%) and 0.31 mL +/- 0.08 (5.9%), respectively. Intraobserver reproducibility error was 0.20-0.65 mL (3.6%-6.4%) for STS and 0.21-0.58 mL (4.2%-6.4%) for FS imaging. Interobserver error was less than 0.62 mL and 7.8%.

CONCLUSION

Three-dimensional data analysis of MR images acquired with STS or FS allows accurate and reproducible volumetric quantification of articular cartilage in the knee.

"Magic-angle" phenomenon: a cause of increased signal in the normal lateral meniscus on short-TE MR images of the knee

OBJECTIVE

Increased signal intensity is frequently present in the upsloping, medial segment of the posterior horn of the normal lateral meniscus on routine short-TE MR images of the knee. This attribute can mimic or obscure abnormalities in this portion of the meniscus. In the present study, we examined whether this appearance could be accounted for by the "magic-angle" phenomenon resulting from the angular orientation of this meniscal segment relative to the static magnetic field.

SUBJECTS AND METHODS

Fifty-eight consecutive knee MR examinations were studied. Sixteen were excluded because of frank evidence of preexisting abnormality of the lateral meniscus. In the remaining 42 examinations, the signal intensity in the medial segment of the posterior horn of the lateral meniscus on short-TE (< 20 msec) sequences was correlated with the angular alignment of this meniscal segment relative to the static magnetic field. In five asymptomatic volunteers, meniscal signal intensities were monitored as the leg was positioned in various degrees of abduction.

RESULTS

Increased signal was present in the medial segment of the posterior horn of the lateral meniscus in 31 (74%) of the 42 patients. In 25 (81%) of these, this meniscal segment was oriented at 55-60 degrees. Increased signal intensity was also present in this meniscal segment in three (60%) of five asymptomatic knees imaged in the neutral position. In each of these, abduction of the leg decreased the meniscal signal by 52-80%. Pathologic evaluation of two menisci showed numerous concentrically arranged collagen fibers.

CONCLUSION

Increased signal in the upsloping portion of the posterior horn of the lateral meniscus on short-TE images often is due to the magic-angle phenomenon rather than to meniscal degeneration or tear.

Cystic lesions around the knee joint: MR imaging findings

A wide variety of cystic lesions may be encountered in the soft tissues and bones during routine MR imaging of the knee. These lesions represent encapsulated fluid collections and exhibit low signal intensity on T1-weighted images and high signal intensity on T2-weighted images because of their high content of free water. Many lesions produce clinical features suggestive of internal derangement of the knee, so correct MR diagnosis is needed to avoid unnecessary arthroscopy and to guide specific therapy. The purpose of this essay is to illustrate the MR appearance of cystic lesions that can be found around the knee and to explain the clinical features and significance of these lesions.

MR imaging of the arthritic knee: improved discrimination of cartilage, synovium, and effusion with pulsed saturation transfer and fat-suppressed T1-weighted sequences

PURPOSE

To assess the applicability of three-dimensional (3D) magnetic resonance (MR) imaging with pulsed saturation transfer (ST) or fat saturation in depicting articular structures in arthritic knees.

MATERIALS AND METHODS

Eleven patients underwent MR imaging with T1-weighted spin-echo (SE); unenhanced and contrast material-enhanced T2*-weighted 3D gradient-echo with and without on-resonance pulsed ST; and T1-weighted, fat-presaturated 3D gradient-echo techniques. Images with ST were subtracted from those without ST.

RESULTS

Both fat-suppressed imaging and ST-subtraction (STS) techniques generated a high contrast-to-noise ratio among cartilage, synovium, effusion, bone, and adipose tissue. Both techniques depicted hypertrophic synovial tissue on unenhanced images; contrast material was necessary to differentiate between synovium and cartilage on STS images.

CONCLUSION

3D MR imaging with fat-suppressed or STS techniques provides good discrimination among articular structures in arthritic knees. Fat-suppressed imaging is faster than STS imaging and offers better contrast between cartilage and synovium. These techniques may improve monitoring of arthritic disease progression and therapeutic response.

Recent advances in magnetic resonance imaging of the musculoskeletal system

Numerous recent technical innovations in magnetic resonance imaging have dramatically improved the imaging evaluation of musculoskeletal disease; however, with the introduction of new techniques comes the risk of inappropriate applications and unanticipated pitfalls in interpretation. Some of the practical and theoretical implications of these recent innovations as well as potential caveats associated with their use are highlighted in the following discussion.

Association of glenoid labral cysts with labral tears and glenohumeral instability: radiologic findings and clinical significance

PURPOSE

To determine the relationship between labral cysts and labral tears and glenohumeral instability.

MATERIALS AND METHODS

Magnetic resonance (MR), clinical, and arthroscopic examinations of the shoulder and the surgical findings of 20 patients were correlated and retrospectively analyzed. A cystic-appearing mass adjacent to the labrum was the selection criterion for inclusion.

RESULTS

MR imaging showed labral tear intimately associated with cystic-appearing mass in these 20 patients. The tear and cyst complex was located anteriorly in two patients, posteriorly in nine, and superiorly in nine. The mass extended into the spinoglenoid notch in six patients, the suprascapular notch in three, and both notches in four. Physical examination showed glenohumeral instability in the direction of the labral tear and cystic-appearing mass in 11 patients (55%). Findings at intraarticular surgery, performed in eight patients, confirmed a labral tear with communication between the joint space and the cyst.

CONCLUSION

Glenoid labral cysts are associated with glenoid labral tears and shoulder instability.

Large telangiectatic focal nodular hyperplasia presenting with normal radionuclide studies: case report

A 9 cm-lesion of telangiectatic focal nodular hyperplasia was incidentally identified in a 31-yr-old female. Despite a typical appearance by X-ray computed tomography and ultrasonography, scintigraphy with technetium-99m-(99mTc) colloid, 99mTc-diethyliminodiacetic acid, and 99mTc-labeled red cells failed to demonstrate any abnormalities. These findings are felt to reflect the relative lack of architectural disruption that histologically characterizes this particular lesion. The present report described the imaging characteristics of the telangiectatic form of focal nodular hyperplasia.