Meniscal tears on 3T MR: Patterns, pearls and pitfalls

Transcription

1 Meniscal tears on 3T MR: Patterns, pearls and pitfalls Poster No.: C-2221 Congress: ECR 2010 Type: Educational Exhibit Topic: Musculoskeletal Authors: J. C. Kandathil; Singapore/SG Keywords: Knee injuries, Magnetic Resonance Imaging, Diagnostic Imaging DOI: /ecr2010/C-2221 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 29

2 Learning objectives 1. Illustrate the role of 3TMR in imaging of meniscal tears. 2. Describe the imaging findings in different types of meniscal tears including pertinent meniscal anatomy and meniscal variants. 3. Identify potential diagnostic pitfalls. Background MR has a well established role in the diagnosis of meniscal pathology. 3T MR systems are now increasingly used in clinical practice. The higher signal to ratio afforded by 3T imaging increases the speed and enhances spatial and contrast resolution. Images for this section: Page 2 of 29

3 Fig. 1: Sagittal PDFS image showing normal medial mensiscus anterior and posterior horns Page 3 of 29

4 Fig. 2: Sagittal PDFS image showing normal lateral meniscus anterior and posterior horn Page 4 of 29

5 Fig. 3: Coronal PD image showing normal meniscal root Page 5 of 29

6 Imaging findings OR Procedure details Technique: A standard protocol typically includes a short TE sequence (T1 or PD). Proton density or T2 weighted fat saturated sequences are also routinely performed in axial, sagittal and coronal imaging planes. Three-tesla MR imaging allows for a higher SNR compared with 1.5T MR imaging. The spin-spin relaxation time, T2, remains fairly constant at different field strengths. However, the spin-lattice relaxation time, T1, increases as the field strength increases. Therefore, at 3T, the TR must be longer than on 1.5T MR scanners to maximize the SNR gain. Also on 3T MR scanners, the TE must be slightly shorter than on 1.5T MR scanners to account for decreased T2 relaxation time [1,2]. Artifacts: Chemical shift artifact and susceptibility artifacts tend to be more pronounced at 3T. Specific absorption rate also increases with increase in magnet strength. Anatomy: The menisci are wedge-shaped, fibrocartilaginous structures interposed between the articular surfaces of distal femur and proximal tibia. The menisci have a concave superior surface and a flat inferior surface. They cover 50% of the medial and 70% of the lateral surface of the tibial plateau [3]. Each meniscus is divided arbitrarily into an anterior horn, a body and a posterior horn. The medial meniscus is semilunar and bigger than the more circular shaped lateral meniscus. In adults, the vascularized area, commonly known as the ''red zone,'' involves the outer 10% to 30% of the meniscus [3,4]. Page 6 of 29

7 The transverse or anterior intermeniscal ligament, connects the two anterior horns [5]. The meniscofemoral ligaments extend from the posterior horn of lateral meniscus usually to the lateral aspect of the posterior medial femoral condyle. The popliteomeniscal fascicles are synovial attachments of the posterior horn of the lateral meniscus that extend around the popliteus bursa. The normal meniscus is low signal on all pulse sequences. Non surfacing intrasubstance signal is often seen representing meniscal degeneration. In the child or young adult this is thought to represent prominant or persistent meniscal vascularity. Meniscal variants: Common variants include the discoid meniscus, meniscal ossicles and the meniscal flounce. Tear classification: The diagnostic criteria for a meniscal tear in a knee without prior meniscal surgery is either an area of abnormal signal within the meniscus on at least one image that extends to the meniscal articular surface or abnormal morphology of the meniscus [6]. A tear should be described in terms of its location, plane, shape, completeness and length. The location is further described as involvment of the peripheral vascular or red zone (outer third)or inner avascular white zone (inner two third). The plane of the tear is described as vertical, horizontal or oblique. A vertical tear can be longitudinal (parallel to the long axis of meniscus) or radial (perpenedicular to it). A complex tear has both vertical and horizontal tear components, while a parrot beak tear has both a radial and a longitudinal component. A bucket handle tear refers to a specific type of longitudinal tear where the inner fragment is displaced into the intercondylar notch or anterior compartment. Page 7 of 29

8 A flap tear is a short-segment, horizontal meniscal tear with fragments either displaced into the notch or into the superior or inferior gutters. Lastly a root tear occurs at the tibial attachment of the meniscus. It has been described only posteriorly and is often associated with meniscal extrusion [7]. Meniscal Pitfalls: Potential sources of error include tears not visible on MR, those missed by the arthroscopist and those wrongly interpreted by the reporting radiologist. False positives occur with healed meniscal tears and postoperative menisci, where abnormal signal extending to the surface remains on standard MR imaging sequences. Magic angle phenomenon on short TE sequences occuring in the posterior horn of the lateral meniscus because of the central upsloping of the meniscus is also a potential source of error [8]. Abnormal signal having a speckled or spotty appearance on T1 and proton density images can occur in the anterior horn of the lateral meniscus near the central attachment on the most central sagittal images [9]. The normal concavity of the peripheral aspect of the meniscus can mimic a horizontal tear on peripheral sagittal images caused by volumeaveraging. Chondrocalcinosis may demonstrate high signal within the meninscus. Finally the transverse intermeniscal ligament, the meniscal attachments of the meniscofemoral ligaments, the popliteus tendon adjacent to the posterior horn of the lateral meniscus, the medial and lateral oblique meniscomeniscal ligaments and the anterior meniscofemoral ligament of the medial meniscus can all simulate tears. However, following these structures on serial images and evaluating the meniscus in multiple imaging planes can often help prevent these errors. Page 8 of 29

9 Tears involving the meniscal free edge and small meniscal tears are the usual cause of false negatives on MR imaging. Page 9 of 29

10 Images for this section: Page 10 of 29

11 Fig. 1: Sag PDFS image, speckled anterior horn of lateral meniscus Page 11 of 29

12 Fig. 2: Coronal PD image showing a discoid lateral meniscus covering more than 50% of the lateral femoral condyle articular surface Page 12 of 29

13 Fig. 3: Non surfacing signal in the posterior horn of medial meniscus in this sag PDFS image of an adult represents intrasubstance degeneration and not a tear Page 13 of 29

14 Fig. 4: Sag PDFS image showing horizontal cleavage tear of the posterior horn of medial meniscus Page 14 of 29

15 Fig. 5: Coronal PD image demonstrating a peripheral vertical tear involving the posterior horn and adjacent body of medial meniscus Page 15 of 29

16 Fig. 6: Radial tear involving the body of medial meniscus as seen on this sagittal PDFS image Page 16 of 29

17 Fig. 7: Complex tear involving the posterior horn of medial meniscus shown on this PDFS sagittal image Page 17 of 29

18 Fig. 8: Bucket handle tear of the medial meniscus. The displaced fragment is seen beneath the PCL. Page 18 of 29

19 Fig. 9: Double PCL sign. Displaced medial bucket handle fragment in the intercondylar notch parallel and just inferior to PCL. Page 19 of 29

20 Fig. 10: Menisco capsular junction tear involving the posterior horn of medial meniscus shown on this coronal PD image Page 20 of 29

21 Fig. 11: Menisco capsular junction tear as shown on this sag PDFS image Page 21 of 29

22 Fig. 12: Flap tear involving the posterior horn of medial meniscus. The flipped fragment is seen in the intercondylar notch. Page 22 of 29

23 Fig. 13: Displaced fragment from this complex medial meniscus tear seen in the inferior parameniscal recesss Page 23 of 29

24 Fig. 14: Displaced fragment from this complex lateral meniscal tear seen in the superior parameniscal recess Page 24 of 29

25 Fig. 15: Vertical tear of the lateral meniscus immediately adjacent to the meniscal root Page 25 of 29

26 Fig. 16: A more anterior coronal image from the same patient with lateral meniscal root tear demonstrating extrusion of the lateral meniscus Page 26 of 29

27 Conclusion MR imaging of the knee at 3T is sensitive and specific for detecting meniscal tears. The enhanced signal to noise ratio increases spatial and contrast resolution and allow faster and more accurate diagnosis of menical tears. This paper reviews the basic techniques, anatomy and imaging findings of meniscal tears on 3TMR. Personal Information Dr Julio Chacko Kandathil Associate Consultant Department of Diagnostic Radiology Tan Tock Seng Hospital 11 Jalan Tan Tock Seng Singapore References Page 27 of 29

28 [1] Gold GE, Han e, Stainsby J, et al. Musculoskeletal MRI at 3.0 T:relaxation times and image contrast. AJR Am J Roentgenol 2004;183: [2] Gold GE, Suh B, Sawyer-Glover A, et al. Musculoskeletal MRI at 3.0 T: initial clinical experience. AJR Am J Roentgenol 2004;183: [3] Rath E, Richmond JC. The menisci: basic science and advances in treatment. Br J Sports Med 2000;34(4): [4] Hauger O, Frank LR, Boutin RD, et al. Characterization of the ''red zone'' of knee meniscus: MR imaging and histologic correlation. Radiology 2000;217(1): [5] Aydingoz U, Kaya A, Atay OA, et al. MR imaging of the anterior intermeniscal ligament: classification according to insertion sites. Eur Radiol 2002;12(4): [6] De Smet AA, Norris MA, Yandow DR, et al. MR diagnosis of meniscal tears of the knee: importance of high signal in the meniscus that extends to the surface. AJR Am J Roentgenol 1993;161(1): [7] Brody JM, Lin HM, Hulstyn MJ, et al. Lateral meniscus root tear and meniscus extrusion with anterior cruciate ligament tear. Radiology 2006;239(3): [8] Peterfy CG, Janzen DL, Tirman PF, et al. ''Magicangle'' phenomenon: a cause of increased signal in the normal lateral meniscus on short-te MR images of the knee. AJR Am J Roentgenol 1994; 163(1): [9] Helms CA. The meniscus: recent advances in MR imaging of the knee. AJR Am J Roentgenol 2002;179(5): [10] Thomas Magee. Three-Tesla MR imaging of the knee. Radiologic Clinics of North America 45(2007) Page 28 of 29

29 [11] Michael G Fox. MR imaging of the meniscus: Review, Current Trends and Clinical Implications. MR Imaging Clinics of North America 15 (2007) Page 29 of 29