Standard Magnetic Resonance Imaging of the Knee
Guidelines and recommendations for reporting of musculoskeletal imaging examinations
Please send your comments or suggestions to lyao@mail.rad.ucla.edu
Sample Normal Report
Findings:
The menisci are normal in configuration and free of significant signal abnormalities. The cruciate and collateral ligaments are intact. There is no evidence of joint effusion, arthrosis, bony injury, or joint surface defects.
Impression:
Normal MRI of the knee, without evidence of internal derangement.
Hierarchical Diagnostic Check List: MRI of the Knee
Menisci (Normal, Abnormal)
Post operative changes
(present, absent)
Ligaments (Normal,
Abnormal)
Bony injury
(absent, present)
Joint Surface Disease
(absent, present)
Other findings
Meniscal Tears:
Response categories:
A level of confidence modifier is occasionally appropriate in describing a meniscal lesion. Examples of a 'possible' tear would include a linear area of increased signal within a meniscus that appears to contact an articular surface on one image only [1]. A 'probable' tear would include increased intrameniscal signal that approaches only the free edge of a meniscus. In many equivocal cases, ill-defined areas of intrameniscal signal may approach but not definitely extend through an articular meniscal surface on one or two images only (see figure below). The root of the posterior horn lateral meniscus can be particularly problematic because of magic angle phenomenon [2], while the anterior horn lateral meniscus can often normally show Grade 2 signal changes near the tibial attachment [3].
This indistinct area of increased signal in the posterior horn of the medial meniscus does approach the superior surface of the meniscus (arrow) on one sagittal image, and might be regarded as a 'possible' tear. At arthroscopy, there was no tear.
Major diagnostic qualifiers:
It is essential to describe the zones of the meniscus that are involved and the presence of meniscal detachment, if discernible. Clues to detachment include a 'defect' in the meniscus, or a markedly attenuated or small meniscal contour. Alternatively, a flap situated adjacent to an intact meniscal segement may give the appearance of an enlarged meniscal contour. Bucket handle fragments are by definition attached at two ends, and are often centrally displaced toward the tibial eminence. On sagittal images, the bucket handle may be visualized as a 'double PCL' sign [4].
Sagittal image through the lateral compartment depicts attenuated anterior and posterior horns of the lateral meniscus. There are also areas of increased signal that extend to the meniscal surface (arrow). These findings are clues to a large detached tear. A centrally displaced bucket handle fragment was depicted on other images.
Sagittal image through the medial intercondylar region in a different patient shows a large centrally displaced meniscal fragment characteristic of a 'bucket handle tear' (arrows). P= femoral attachment of the PCL.
Minor diagnostic qualifiers for meniscal abnormalities include the following:
Orientation of meniscal tears:
Intrameniscal Location:
Size of tear:
The orientation of meniscal tears may not always be clear, but can usually be classified as either horizontal, vertical, or complex. Vertical tears can be either longitudinal, radial or obliquely oriented, though this classification may be even less reliable. A tear may appear to extend to one meniscal surface (superior, inferior) and not the other. All of these features are helpful to describe when they can be clearly discerned. There is little evidence documenting the reliability of MRI for determining the size of tears; the binary distinction we recommend is therefore conservative.
The location of the tear with respect to the cross-sectional meniscal anatomy may be important, especially for detached tears. A tear in the outer one-third of the meniscus is considered 'peripheral', and may be amenable to repair. Similarly, meniscocapsular separations may heal (figure below), and are repairable, but MRI is likely insensitive for this diagnosis [5].
Sagittal T2-weighted image depicts findngs of acute meniscocapsular separation at posterior horn of the medial meniscus. T2-weighted images are essential for diagnosis. High signal at the base of the meniscus (arrows) is the clue to diagnosis (SM=semimembranosus tendon). Chronic lesions are easily missed. On the lateral side, fluid in the popliteal hiatus should not be misinterpreted as a meniscocapsular separation.
1. Dillon EH, Pope DF, Jokl P, Lynch K. The clinical significance of Stage 2 meniscal abnormalities on magnetic resonance knee images. Magnetic Resonance Imaging 1990;8:411-415.
2. Peterfy CG, Janzen DL, Tirman PFJ. Magic Angle phenomnon: Cause of increased signal in the normal lateral meniscus on short-TE MR images of the knee. AJR 1994;163:149.
3. Shankman S, Beltran J. Anterior Horn of the lateral meniscus; Another potential pitfall in the MR imaging evaluation of the knee. Presented at the 1996 Annual Meeting of the RSNA.
4. Wright DH, DeSmet AA, Norris M. Bucket-handle tears of the medial and lateral menisci of the knee: Value of MR imaging in detecting dispaced fragments. AJR 1995;165:621.
5. Rubin DA, Britton CA, Towers JD, Harner CD. Are MR Imaging signs of meniscocapsular separation valid? Radiology 1996;201:829-836.
Exclusions from Diagnostic Qualifiers for Meniscal Tears
An ill defined region of increased intrameniscal signal is present in the posterior horn of the medial meniscus in this 14 year old male, who went on to develop a large bucket handle tear several months later. Although this likely represented a true 'intrasubstance' tear, such findings cannot be reliably distinguished from mucoid degeneration or other causes for 'grade 1' signal changes, especially in older patients. Whether the signal intensity of such changes, particularly on T2 weighted images, is diagnostically useful remains to be shown.
Anterior Cruciate Ligament
Response categories:
Evaluation of the ACL should be unequivocal, save technical shortcomings. Most ACL ruptures can be diagnosed reliably on sagittal images alone, where discontinuity, an abnormal course, or waviness of low signal fibers will be depicted. Diagnosis may be assisted by coronal and axial imaging, which help confirm thickening or hyperintensity at femoral attachment of ACL.
Minor diagnostic qualifiers for ACL rupture
Chronic ACL ruptures can be recognized by a lack of edema and thickening of the ligamentous substance. Low signal fibers of the ACL in chronic ruptures may be well seen, but will be abnormal in course, often scarred down to the PCL [3].
Exclusions from diagnostic qualifiers for ACL ruptures
It is tempting to 'grade' ACL injuries, particularly in equivocal cases where findings may be subtle. There is no evidence supporting the utility of MRI for grading the severity of ACL ruptures [1,2], and such an estimation may even be difficult at arthroscopy. A biomechanically 'partial' ACL rupture is likely an unusual occurence.
1. Yao L, Gentili A, Petrus L, Lee JK. Partial ACL rupture: An MR diagnosis? Skeletal Radiol 1995;24:247-251.
2. Umans H, Wimpfheimer O, Haramati N, et al. Diagnosis of partial tears of the anterior cruciate ligament of the knee: Value of MR imaging. AJR 1995;165:893.
3. Vahey TN, Broome DR, Kayes KJ, Shelbourne KD. Acute and chronic tears of the anterior cruciate ligament: Differential features at MR imaging. Radiology 1991;181:251-253.
Posterior Cruciate Ligament
Response categories:
Evaluation of the PCL should be unequivocal and can be diagnosed reliably on sagittal images alone, where discontinuity or signal abormalities in the ligament substance will be depicted.
Minor diagnostic qualifiers for PCL rupture
Given the thicker caliber of the PCL compared to the ACL, it is better depicted on MRI. Local signal abnormalities in the PCL can be seen while continuity of some ligamentous fibers is preserved. Some evidence suggests that such MR lesions can be intepreted as 'partial' ruptures, although further studies are needed [1]. 'Complete rupture' should be diagnosed when ligamentous continuity is entirely lost on sagittal MRI. This recommendation differs from that for ACL ruptures.
High signal intensity (short arrow) on T2 weighted image indicates complete PCL rupture. Note sparring of the meniscofemoral ligaments (long arrows).
Sagittal proton density image in a different case depicts irregular area of mildly increased signal within portions of the PCL, consistent with a partial rupture. At arthroscopy, this injury was estimated to represent a 20% rupture of the PCL. MRI findings may predict the severity of PCL--but likely not ACL--injuries.
1. Patten RM, Richardson ML, Zink-Brody G, et al. Complete vs partial-thickness tears of the posterior cruciate ligament: MR findings.JCAT 1994;18:793-799.
Collateral Ligaments
Response categories:
Coronal images are used to evaluate the collateral ligaments. Little data exists on the MRI evaluation of the fibular collateral ligament. New data is emerging, however, on the detailed findings in injuries of the posterolateral corner of the knee. Injuries of the tibial collateral ligament appear as regions of ligamentous discontinuity, thickening, or waviness. Longitudinal increased signal within the ligament can create a striated appearance to the ligament. Long TE images are probably essential in assessing injury severity.
Minor diagnostic qualifiers
MRI probably has only a modest ability to grade the biomechanical severity of collateral ligament injuries. The discernment of two grades is thus deliberately conservative. Hi grade injuries are manifested by discontinuities in the ligamentous substance, and areas of hyperintensity within the ligament on T2 weighted images [1,2]. The 'hi grade' MRI injury likely corresponds to both Grade II and III injuries by clinical exam.
In some cases, injuries may be localized in nature. In such cases it may be helpful to indicate where the injury is within the ligament, especially when repair may be contemplated.
Coronal T2 weighted image shows hyperintensity within the proximal fibers of the tibial collateral ligament, with associated thickening or swelling of the ligament substance. Such findings on T2 weighted images are indcative of higher grade (clinical Grade II-III) sprains.
1. Rasenberg EI, Lemmens AM, van Kampen A. Grading medial collateral ligament injury: Comparison of MR imaging and instrumented valgus-varus laxity test-device. A prospective double-blind patient study. European J Radiol 1995;21:18-24.
2. Yao L, Dungan D, Seeger LS. MR imaging of tibial collateral ligament injury: Comparison with clinical examination. Skeletal Radiol 1994;23:521-524.
Cruciate reconstruction
response categories (absent, present)
Major diagnostic qualifier:
Minor diagnostic qualifier:
Extra-articular procedures to stabilize the cruciate deficient knee have been largely supplanted by tendon graft reconstructions, most commonly using central third-patellar tendon grafts. Graft ruptures may be detected when no low signal fibers of the graft remain in continuity on long TE images (figure below). Increased signal within the graft may be seen, however, with graft impingement. This distinction can be problematic [1].
MRI is not generally used to detect graft position, however graft malpositions are viewed to advantage on MRI compared to radiography [2]. The ACL graft should parallel the roof of the intercondylar notch with the knee in full extension. The tibial tunnel should enter the joint at a point 25-50% of the AP tibial diameter behind the anterior tibial margin [3]. A more vertical position of the ACL graft may compromise its function. Impingement occurs when the anterior and inferior aspect of the roof of the notch indents the ACL graft in full extension.
When T2 weighted image depicts discrete interruption of low signal graft fibers (arrow), diagnosis of graft rupture can be more confidently made (asterisks = margins of torn graft ). Proton density or T1 weighted images cannot be used to make this diagnosis, and alterations in graft signal secondary to impingement can be confused with ruptures, even on T2-weighted images.
1. Howell SM, Berns GS, Farley TE. Unimpinged and impinged anterior cruciate ligament grafts: MR signal intensity measurements. Radiology 1991;170:639-643.
2. Deutsch AL, Mink JH, Fox JM, Friedman MJ, Howell SM. The postoperative knee. Magnetic Resonance Quarterly 1992;8:23-54.
3. Tomczak R J, Hehl G, Mergo PJ, Merkle E, Rieber A, Brambs H J. Tunnel placement in anterior cruciate ligament reconstruction: MRI analysis as an important factor in the radiological report. Skel etal Radiology 1997;26:409-413.
Trabecular Injury
Response categories: (present, absent)
Definition: Trabecular injury is an MR diagnosis based on the finding of marrow edema in areas of impact or bony stress sustained from trauma. This pattern should not be accompanied by cortical abnormalities, or low signal medullary findings (MR fracture lines) that extend to the cortex. Synonyms include bone bruise, occult intraosseous fracture.
Minor Diagnostic Qualifiers
The location of trabecular injury can illuminate injury mechanism, or serve as a secondary sign of ACL rupture. In ACL ruptures, the marrow findings are characteristically located in the postolateral tibial plateau, and the mid lateral femoral condyle. Transient patellar disclocations may be recognized by trabecular (or osteochondral ) injury in the anterolateral femoral condyle, and in the patellar apex.
Caveats: Marrow edema is non-specific, and can be seen in a variety of conditions, including stress fractures. History and location are essential features for diagnoses.
Bony Injury
Response categories: present/absent
Definitions: Traumatic fractures and osteochondral fractures are distinguished from occult trabecular injury by the presence of discontinuity or deformity of low signal cortical lines, or by the presence of 'MRI fracture lines,' which are low signal lines in the medulla extending to the cortex. If the MRI fracture lines only extend to the subchondral cortex, then the lesion is an osteochondral fracture, rather than an intra-articular fracture.
Acute bony injuries will be accompanied by a marrow edema pattern: speckled or confluent low signal in the medulla onT1-weighted images; specked or ill defined hyperintensity in the medulla on long TE or STIR images.
Major diagnostic qualifiers for fractures and osteochondral fractures:
The location of bony injuries can be a clue to injury mechanism. In addition to the extent of joint surface involvement, the degree of displacement at the joint surface (depression or joint surface gap) is important in deciding treatment.
Sagittal proton density (left) and T2 weighted (right) spin echo images identify occult intra-articular fracture of the lateral tibial plateau, characterized by low signal 'MRI fracture line' (arrows) which extend to both subchondral and posterior non-articular cortex. Fracture was not visible on radiographs.
Irregularity in subchondral cortex (arrows) and overlying defects in hyaline cartilage of lateral femoral condyle are visible on this sagittal T2 weighted image. There is little associated marrow edema in this case of chronic ACL deficiency. Findings are consistent with remote osteochondral injury. This kind of bony injury frequently accompanies ACL ruptures.
Medial or Lateral Meniscal Remnant Tear
Response categories: (absent, possible, probable)
MRI has limited efficacy for diagnosing tears in the post-operative meniscus. Pre-existing meniscal signal changes my be mistaken for remnant tears. A levels of confidence modifier for reporting a remnant tear is almost always appropriate. MR arthrography may aid the detection of these lesions [1].
A remnant tear is most reliably manifested as a Grade III signal change within the remnant that is present on T2 weighted images.
Major Diagnostic Qualifiers:
1. Applegate GR, Flannigan BD, Tolin BS, Fox JM, Del Pizzo W. MR diagnosis of recurrent tears in the knee: Value of intraarticular contrast material. AJR 1993;161:821-825.
Chondromalacia
Response categories for chondromalacia:
Routine MRI is probably insensitive for low grade chondromalacia1[1], and sufficient evidence does not exist to warrant the routine use of a 4 or even 3 stage MRI grading system for chondromalacia analagous to arthroscopic grading systems [2]. MR findings for chondromalacia include: Signal heterogeneity within hyaline cartilage, particularly on T2 weighted images; focal hyperintensity within hyaline cartilage, particularly linear; focal defect in hyaline cartilage; irregular contour to the surface of the hyaline cartilage.
The modifier 'severe' should be used where changes are present in an area greater than 1 cm in diameter, or where full thickness focal defects are present. Full thickness disease is distinguished from a 'chondral defect' by the focality of the latter lesion, which lacks surrounding, more diffuse abnormalities. The term 'chondral defect' implies that the lesion is more likely traumatic than degenerative or attritional in etiology.
Major diagnostic qualifier:
1. Gagliardi JA, Chung EM, Chandnani VP et al. Detection and staging of chondromalacia patellae: Relative efficacies of conventional MR Imaging, MR arthrography and CT arthrography. AJR 1994;163:629-636.
2. Shahriaree H. Chondromalacia. Contemp Orthop 1985;11:27-39.
Chondral defect (absent, present)
Focal tears can occur in hyaline cartilage as a result of shearing injuries across the joint surface, and they may create mechanical symptoms mimicking meniscal pathology. These are best depicted on T2 weighted spin echo or T1 weighted gradient echo images [1], where they are seen as focal signal abnormalities along the joint surface that spare the subchondral cortex. These lesions may also be termed chondral fractures or fracture- separations of artcular cartilage. In chronic cases, the MRI findings may overlap with those of chondromalacia.
Full thickness chondral defect is seen as a high signal joint surface lesion (black arrow) surrounded by normal hypointense hyaline cartilage on this spin echo T2 weighted image. Marrow edema is characteristically absent.
1. Disler DG, McCauley TR, Wirth CR, Fuchs MD. Detection of knee hyaline cartilage defects using fat-suppressed three-dimensional spoiled gradient-echo MR imaging: Comparision with standard MR imaging and correlation with arthroscopy. AJR 1995;165:377-382.
Patellar Tendinosis
Response categories: (absent, present)
Minor diagnostic qualifier: (acute, chronic)
Tendinosis is a general rubric which includes a spectrum of disease, including acute and chronic tendonitis and partial tendon ruptures. Findings in tendinosis include hyperintensity within the tendon on short TE > long TE images, and thickening of the tendon. The medial aspect of tendon is predilected [1]. Acute or symptomatic lesions ('tendinitis') are more likely associated with prominent findings on long TE images [2]. Patellar tendinosis is frequently subclinical, and is almost always managed conservatively.
MRI may be useful to gauge the severity of tendinosis by depicting the size of tendon abnormalities. The extent of hyperintensity on T2-weighted or STIR images may be of prognostic value, but further studies in this area are needed.
1. Yu JS, Popp JE, Kaeding CC, Lucas J. Correlation of MR imaging and pathologic findings in athletes undergoing surgery for chronic patellar tendinitis. AJR 1995;165:115-118.
2. McLoughlin RF, Raber EL, Vellet AD, Wiley JP, Bray RC. Patellar tendinitis: MR imaging features with suggested pathogenesis and proposed classification. Radiology 1995; 197:843.
Periarticular Cyst or Ganglion
Well defined, fluid signal, occasionally sepatated masses are frequently encountered, and their location and MRI appearance can aid proper diagnosis of these lesions as periarticular cysts or ganglia [1]. A synovial cyst is synovial lined and arises in locations where synovium ordinarily resides (periarticular or peribursal). A ganglion is non-synovial lined and contains thick gelatinous material. Location rather than any specific MRI features occasionally serves to distinguish these lesions. Numerous bursa also reside about the knee joint and may become visible when inflammed or fluid filled. The term 'peri-articular cyst' is loosely applied to encompass all of these fluid signal masses.
Diagnostic Qualifiers for Periarticular Cysts or Ganglia
Caveats:
A 'meniscal cyst' is a periarticular cyst that develops at the base of a torn meniscus (figure below). These predominate around the mid zone of the lateral meniscus [2].
Synovial cysts frequently arise in the area of the gastrocnemius tendon origin.
Bursa around the knee include: gastrocnemius semimembranosus bursa (Baker's cyst), pes anserine bursa, tibial collateral ligament bursa [3], semimembranosus-tibial collateral ligament bursa [4].
Ganglia occasionally arise within or in close association with the cruciate ligaments, where they may erode adjacent bone.
Coronal proton density image depicts well defined mass (short arrow) at posteromedial joint line, adjacent to the base of a torn meniscus (long arrow). Findings are consistent with a meniscal cyst.
1. Janzen DL, Peterfy CG, Forbes JR, et al. Cystic lesions around the knee joint: MR imaging findings. AJR 1994;163:155.
2. Tasker AD, Ostlere SJ. Relative incidence and mophology of lateral and medial meniscal cysts detected by magnetic resonance imaging. Clin Radiol 1995;50:778.
3. Lee JK, Yao L. Tibial collateral ligament bursa: MR imaging. Radiology 1991;178:855-857.
4. Rothstein CP, Laorr A, Helms CA, et al. Semimembranosus-tibial collateral ligament bursitis: MR imaging findings. AJR 1996;166:875.
Masses
Response categories: (present, absent)
The imaging approach to soft tissue masses or bone tumors is beyond the scope of this general diagnostic checklist. MRI is typically less helpful for making specific diagnoses than for defining the precise extent of mass lesions. MRI can suggest specific diagnoses for lesions that are fat-containing, vascular in origin, or cystic. Caution should be exercised in diagnosing a lesion as a peri-articular cyst if the location of the lesion is in any way atypical.
Major Diagnostic Qualifiers for Soft Tissue Masses
from the
UCLA Department of Radiological Sciences
Los Angeles, California
Amilcare Gentili, MD
Introduction
Improving the precision of the radiology report can enhance the quality of care. The clarity and accuracy of the written report becomes more imperative in this growing era of population-based medicine, more efficient information systems andthe emergence of large, unified patient databases that may be used to assess patient outcomes. Such assessments may increasingly shape guidelines for medical practice.
A standardized reporting system has been proposed and widely implemented for mammography (BI-RADS). Other modalities and organ systems could benefit from similar sytems. We propose standardized guidelines for the reporting of MR examinations of the knee and shoulder, and radiographic examinations of total hip arthroplasty. Rationale for the chosen terminology ('lexicon') and diagnostic categories are provided. Some supportive documentation is provided but the recommendations are meant to be concise rather than didactic.
The diagnostic categories are not intended to be exhaustive lists, but should encompass all important 'major' findings, and most clinically significant 'minor' findings encountered in daily practice. While the guidelines are easily 'codable,' specific codes are not proposed.
Naturally, the appropriateness of diagnostic criteria and descriptors will evolve as technology and our understanding of disease improve. The recommendations reflect our best conception of the capabilities of diagnostic modalities as they are employed in everyday, state of the art practice.
We hope that these guidelines may both educate and improve communication. Comments from viewers are most welcome and encouraged.
General
Guidelines for Reporting Post
Arthroplasty Radiographs of the Hip. Magnetic
Resonance Imaging of the Knee.Magnetic
Resonance Imaging of the Shoulder.
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