Musculoskeletal MRI: A Computer-Based Case Review

1. Musculoskeletal MRI: A Computer-Based Case Review Christopher Wedding, M.D., Daniel Zee, M.D. Patrick M. Colletti, M.D. Department of Radiology, Keck USC School of Medicine, Los Angeles, CA

2. Case 1History:23 year old with painand swelling in left knee

3. Serial Sagittal PD

4. Serial Coronal PD

5. Serial Fat Saturation Sagittal PD

6. Coronal Fat Saturation PD, post-contrast

7. Findings:

8. Findings • Coronal and Sagittal PD MR images show lobulated heterogeneous soft tissue mass about the knee joint, with areas of intermediate-to-low signal intensity and areas of osseous erosions • Sagittal FS PD show similar findings • Coronal FS PD with contrast shows heterogeneous avid enhancement, with persistent areas of low signal intensity

9. Coronal and Sagittal PD MR images show lobulated heterogeneous soft tissue mass about the knee joint, with areas of intermediate-to-low signal intensity

10. Sagittal FS PD show findings similar to the PD MR images, with a lobulated, heterogeneous mass with areas of low signal intensity Coronal FS PD with contrast shows heterogeneous avid enhancement, with persistent areas of low signal intensity

11. Diagnosis:Pigmented Villonodular Synovitis (PVNS)

12. Typically presents in third or fourth decade Intermittent pain and swelling, with decreased range of motion Approx. 80% of cases affect the knee; other large joints affected in decreasing order of freq. include the hip, ankle, shoulder, and elbow Often an assoc joint effusion w/ serosanguinous or xanthochromic fluid Grossly, the lesion has appearance of “shaggy red beard” because of frondlike synovial projections containing hemosiderin (imparting red color) Surgery is preferred treatment, but recurrence rates are high (near 50%) Malignant transformation is exceedingly rare Pigmented Villonodular Synovitis (PVNS)

13. Radiographs may demonstrate a noncalcified soft tissue mass, joint effusion, or erosive changes (with well-defined thinly sclerotic margins) Joint space and bone density typically preserved Radiographs may be normal MRI appearance is often characteristic, with heterogeneous synovial mass, low-intermediate signal intensity on T1-weighted images, with similar signal characteristics on T2-weighted images (due to hemosiderin) Pigmented Villonodular Synovitis (PVNS)

14. Pigmented Villonodular Synovitis (PVNS) • Thedifferential diagnosis for low signal intensity lesions on T1 and T2 in and around the joint: • PVNS • Gout (low signal due to fibrous tissue, hemosiderin, or calcification) • Primary or secondary amyloidosis • Fibrous lesions • Disorders causing hemosiderin deposition (e.g. hemophilia, synovial hemangioma, neuropathic osteoarthropathy)

15. Case 2 History:47 year old female withpain and “locking” in knee

16. Serial Sagittal PD

17. Serial Coronal PD

18. Findings:

19. Findings • Sagittal PD MR images demonstrate an abnormal low signal intensity structure anterior to the posterior cruciate ligament, producing a “double PCL” sign • Coronal PD MR images demonstrate show this same abnormal low signal intensity structure in the intercondylar notch, inferior to the PCL • This low intensity structure represents a displaced meniscal fragment from a torn meniscus

20. Displaced fragment lying inferior to PCL in intercondylar notch “Double PCL” sign, with displaced meniscal fragment lying anterior to normal PCL

21. Diagnosis:Bucket-Handle Tear ofMedial Meniscus with“Double PCL Sign”

22. The menisci are important in load bearing and knee function; up to 50% of load bearing is transmitted in extension and 85% in flexion Tears in the menisci may result from acute trauma or repetitive trauma Medial meniscus is injured more commonly than lateral Acute tears are usually due to athletic injuries with crushing of the meniscus between the tibia and femoral condyles Patients present with knee pain; “locking,” which is usually related to bucket-handle tear; or “giving way,” which is often related to pain; frequently complain of “pop” or “clunk” with motion Meniscal Tears

23. A bucket-handle tear consists of a longitudinal tear of the meniscus, running parallel to the main axis of the meniscus, with displacement of the inner fragment The term "bucket-handle tear" relates to its appearance, in which the inner, displaced meniscal fragment resembles a handle and the peripheral, nondisplaced part resembles a bucket Bucket-Handle Meniscal Tears

24. Several signs are associated with bucket-handle tears “Absent bowtie sign”: when fewer than two bowtie segments of the meniscus are present on sequential sagittal MR images “Flipped meniscus sign”: displaced fragment lies directly on anterior horn, producing an abnormally tall (>6 mm) anterior horn “Double PCL sign”: when the displaced meniscal fragment lies below the PCL, giving the appearance of two ligaments Loose bodies or fragments of menisci in the intercondylar notch may also be seen Bucket-Handle Meniscal Tears

25. Pitfalls in Meniscal Imaging • May only see one “bowtie” in children or small adults (should be bilateral); post-operative knee (with debridement of free edge); older adults and severe osteoarthritis (with thinning of meniscus due to wear of free edge) • Transverse ligament: in anterior aspect of knee in Hoffa’s fat pad; connects anterior horns of medial and lateral menisci; may be mistaken for tear of anterior horn • Meniscofemoral ligament: originates on medial femoral condyle, runs obliquely across knee in intercondylar notch; runs anterior (ligament of Humphry) or posterior (ligament of Wrisberg) to the PCL, and inserts into the posterior horn of the lateral meniscus

26. Pitfalls in Meniscal Imaging • Popliteus tendon pseudotear: originates on the lateral femoral condyle and extends inferiorly between the posterior horn of the lateral meniscus and the joint capsule; it runs obliquely and extends posterior to join the muscle belly, which lies just posterior to the proximal tibia; can mimic a tear of posterior horn of lateral meniscus • Speckled anterior horn of lateral meniscus: caused by fibers of ACL inserting into meniscus, giving a speckled appearance, can resemble a macerated or torn anterior horn

27. Case 3History:29 year old male with left knee pain, s/p trauma

28. Serial Sagittal PD

29. Serial Sagittal Fat Saturation PD

30. Serial Coronal T1

31. Findings:

32. Findings • Sagittal PD MR images demonstrate intermediate signal in the posterior cruciate ligament (instead of the normal low signal) • Additionally, on sagittal PD, there is a curvilinear band of very low signal at the site of the PCL attachment to the tibia, displaced from the tibia • Sagittal fat saturation PD also demonstrates the aforementioned findings, along with a large knee effusion • Coronal T1 images demonstrate a defect in the cortical margin of the proximal tibia

33. Sagittal PD MR images demonstrate abnormally increased signal intensity in the posterior cruciate ligament Additionally, there is a curvilinear band of low signal at the site of the PCL attachment to the proximal tibia; this low signal approximates that of cortical bone

34. Sag FS PD MR images show findings similar to the Sag PD, with increased signal in the PCL, an abnormal low density structure representing avulsed cortical bone, and a large effusion Suprapatellar effusion Torn PCL Avulsed fragment Coronal T1 images demonstrate a defect in the proximal tibia, at the site of attachment of the PCL

35. Diagnosis:Posterior Cruciate Ligament Tear(with avulsion fracture)

36. The PCL arises from the posterior part of the intercondylar area of the tibia, passes superiorly and anteriorly on the medial side of the ACL to attach to the anterior part of the lateral surface of the medial condyle of the femur The PCL tightens during flexion of the knee joint, preventing anterior displacement of the femur on the tibia or posterior displacement of the tibia on the femur It also helps prevent hyperflexion of the knee joint In the weight-bearing, flexed knee, the PCL stabilizes the femur (e.g. when walking downhill) Posterior Cruciate Ligament Tear

37. PCL tears are less common than ACL tears Mechanism of injury usually direct blow to anterior aspect of knee while the knee is in flexion, e.g. a car accident in which the knee strikes the dashboard, striking just below patella, forcing tibia posteriorly, tearing the PCL Because of the force mechanism required to rupture the PCL, isolated complete PCL tears are not common; these tears occur more frequently in combination with injuries to other ligaments of the knee Posterior Cruciate Ligament Tear

38. The normal PCL is a gently curved, homogeneously low signal structure When the PCL tears, it typically does not have an actual disruption of the fibers, but instead stretches and is no longer structurally competent On PD or T1, the PCL takes on uniform diffuse intermediate signal intensity and is thicker than normal The torn PCL does not exhibit high signal on T2WI, although some reports demonstrate high signal on STIR Posterior Cruciate Ligament Tear

39. Another example ofPCL tear:33 year old male with right knee pain, s/p motorvehicle accident

40. Serial Sagittal PD

41. Serial Sagittal PD with Fat Saturation

42. Sagittal FS PD MR images demonstrate increased marrow signal in the proximal tibia, secondary to mechanism of injury (“knee-to-dashboard” injury) Note the large, high signal intensity knee effusion Sagittal PD MR images demonstrate intermediate signal in the posterior cruciate ligament, consistent with tear

43. Case 4History:55 year old male withright knee pain

44. Serial Coronal T1

45. Serial Sagittal Fat Saturation PD

46. Findings:

47. Findings • Coronal T1 MR images demonstrate a discrete area of subchondral decreased signal intensity involving the weight bearing portion of the medial femoral condyle • Sagittal FS PD MR images demonstrate diffuse increased signal intensity within subchondral bone and a high signal intensity joint effusion

48. Coronal T1WI demonstrates an area of subchondral decreased signal intensity involving the weight bearing portion of the medial femoral condyle Sagittal FS PD demonstrates increased subchondral marrow signal intensity in the medial femoral condyle and a high signal intensity knee effusion

49. Diagnosis:Spontaneous Osteonecrosis of the Knee (SONK)

50. As the name implies, this clinical entity is defined as necrosis of the weight bearing portion of the femur or tibia with associated subchondral fracture and collapse Typically occurs in ages 50 and older, more common in females Intense pain often after trivial trauma Weight-bearing portion of medial femoral condyle most commonly affected, but lateral femoral condyle can also be affected Pain may resolve spontaneously; alternatively, larger lesions may progress to secondary degenerative disease Spontaneous Osteonecrosis of the Knee (SONK)