Do Not Fall on Your Knees - Recognizing Common and Uncommon Pitfalls that May Simulate Meniscal Tears

Do Not Fall on Your Knees - Recognizing Common and Uncommon Pitfalls that May Simulate Meniscal Tears Poster No.: C-1146 Congress: ECR 2016 Type: Educational Exhibit Authors: P. Musa Aguiar, J. Goncalves, A. C. Valim, F. B. M. D. 1 1 2 1 1 1 1 2 Ferreira, A. Y. Aihara, F. Cardoso ; Sao Paulo/BR, BRASÍLIA/ BR Keywords: Education and training, Education, MR, Musculoskeletal system, Musculoskeletal joint, Anatomy DOI: 10.1594/ecr2016/C-1146 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. www.myesr.org Page 1 of 19

Learning objectives The aims of this educational exhibit are: 1. To discuss the anatomy and imaging features of the menisci. 2. To review pitfalls in meniscal imaging and perimeniscal structures, that may be confused with pathological findings, in order to diminish reporting errors. Background The knee is the most imaged joint at magnetic resonance imaging (MRI). Technological advances allows progressive improvements in the depiction of anatomical details and in the diagnosis of meniscal lesions. Unfortunately, there are many anatomical variations and some of them may be mistaken for pathological conditions. Recognizing meniscal anatomic variants is, therefore, essential to avoid potential interpretation pitfalls. This poster reviews anatomic variants of size and shape of the menisci and also meniscoligamentous structures that may potentially be confused with pathological findings. Findings and procedure details RELEVANT NORMAL ANATOMY AND MRI APPEARANCE The menisci of the knee are crescent-shaped fibrocartilaginous structures that are interposed between the articular surfaces of the distal femur and the proximal tibia. The menisci are thick peripherally and taper centrally to a thin free edge, therefore appearing triangular in shape in coronal and sagittal MRI. The medial meniscus is semilunar in shape and larger than the more circular C-shaped lateral meniscus. On sagittal images, the anterior and posterior horns of the lateral meniscus are nearly equal in size, whereas the posterior horn of the medial meniscus is nearly twice the size of the anterior horn Fig. 1 on page 5. The entire periphery of the medial meniscus is firmly attached to the joint capsule and deep fibers of the tibial collateral ligament at the level of the mid-body; in contrast, the lateral meniscus is more mobile, with its anterior horn and body of the lateral attached to Page 2 of 19

the joint capsule, but with separation of the posterior horn from the capsule, connected to it via superior and inferior popliteomeniscal fascicles (popliteal hiatus) Fig. 2 on page 5 Fig. 3 on page 6. Because of its fibrocartilaginous composition, the normal menisci demonstrate low signal intensity on all MRI pulse sequences, with the exception of children and young adults, which can present non-surfacing intrameniscal signal that corresponds to prominent or persistent meniscal vascularity. DISCOID MENISCUS A discoid meniscus is an abnormally tall and elongated meniscus covering more than 50% of the weight bearing aspect of the femoral condyle or with a transverse width of 14 mm in the mid portion of its body [1] [2] Fig. 4 on page 7. In the sagittal plane, the meniscus is seen with a continuous connection between the anterior and posterior horns, in more than three consecutive images. It affects more commonly the lateral meniscus. Their abnormal morphology predisposes them to increased stress, thus resulting in higher incidence of lesions. RING MENISCUS A ring meniscus variant is similar to a thin membranous discoid meniscus in which the central membrane is deficient and the anterior and posterior horns are connected by an inner bridge Fig. 5 on page 7. This can be misinterpreted for a centrally displaced bucket-handle tear Fig. 6 on page 8, but the triangular shape of the central inner horn component should prompt this diagnosis [3]. SPECKLED ANTERIOR HORN The anterior horn of the lateral meniscus has fibers of the ACL that extend into it at the anterior root where it attaches to the tibial plateau centrally. Variability in the interweaving of fibers of the ACL with those of the anterior horn at the tibial insertion of the ACL may determine a spotty hyperintense signal within the anterior horn of the lateral meniscus on T2WI and PDWI on the two most central images of the meniscus, simulating a lesion Fig. 7 on page 9. MENISCAL FLOUNCE Meniscal flounce is commonly observed within the medial meniscus [3]. It is thought to be related to transient physiologic distortion that produces a wavy contour along the inner edge of a meniscus Fig. 8 on page 9, which can be mistaken for a radial tear on coronal images because of apparent truncation of the inner edge of the meniscus determined by partial-volume effects [2]. Page 3 of 19

MENISCAL OSSICLE They are rare and comprise foci of intrameniscal ossification, usually within the posterior horn of the medial meniscus, thought to be developmental in origin, although some may be related to dystrophic calcifications following trauma [2]. Meniscal ossicles can be identified as a focal lesion surrounded by the meniscus, with signal intensity that parallels that of marrow fat Fig. 9 on page 10. The differential diagnosis should be made with osteochondral loose bodies. TRANSVERSE MENISCAL LIGAMENT Anterior horns of the menisci are connected to each other by the transverse meniscal ligament in up to 58% of patients [4], and the attachment site of this ligament on the meniscus can sometimes mimic a meniscal tear, as it runs parallel to the anterior horn the lateral meniscus for a short distance, before inserting into it [2] Fig. 10 on page 11. Sagittal imaging at this level can, therefore, mislead the reader to diagnose a meniscal tear. This can be avoided by characterizing the course of this linear structure of hypointense signal on several sequential sagittal images Fig. 11 on page 11. MENISCOFEMORAL LIGAMENT They are anatomically inconstant structures that run from the posterior horn of the lateral meniscus to the lateral aspect of the medial femoral condyle or to the posterior cruciate ligament [5]. If anterior to the PCL, it is called Humphrey ligament, and if it lies posterior to it, Wrisberg ligament. On sagittal images it is seen as a hypointense oval structure anterior or posterior to the PCL Fig. 12 on page 12. On coronal images it is characterized as an oblique band with hypo-intense signal in the posterior aspect of the intercondylar notch Fig. 13 on page 13. If prominent, a Humphrey ligament may be misinterpreted as a bucket handle tear Fig. 14 on page 13. They also can mimic a tear at their attachment site to the central aspect of the posterior horn of the lateral meniscus. Tears at the junction of the meniscofemoral ligament and the posterior horn are called "Wrisberg rip" Fig. 15 on page 14, and are typically associated with ACL tears and rotational biomechanics implicated in such lesion. ANTEROMEDIAL MENISCOFEMORAL LIGAMENT This rare accessory ligament extends from the anterior horn of the medial meniscus, distinctly covering all length of the anterior cruciate ligament, to insert into the medial wall of the lateral femoral condyle, next to the ACL insertion Fig. 16 on page 15 Fig. 17 on page 15. OBLIQUE MENISCOMENISCAL LIGAMENT Page 4 of 19

This uncommon (2-4% of patients) [5] intermeniscal ligament connects the posterior horn of one meniscus to the anterior horn of the contralateral meniscus Fig. 18 on page 16. Both medial and lateral oblique meniscomeniscal ligament exist and are named according to their anterior meniscal origin [1]. Its importance lies in the fact that it might be mistaken for a bucket handle tear or a displaced meniscal flap, especially on sagittal images, as it crosses the intercondylar incisure intermingled with the cruciate ligaments. Its trajectory can be traced throughout its entire course on coronal and/or axial images to differentiate it from a true lesion. Images for this section: Fig. 1: - NORMAL MENISCI A)Sagittal T2-W fat- suppressed image of the lateral meniscus shows the anterior and posterior horns (asterisks) which are similar in size and shape. Segment of the popliteous tendon (arrow) is also seen. B)Sagittal T2-W fatsuppressed image of the medial meniscus demonstrates that the posterior horn (triangle) is larger than the anterior horn (asterisk) Page 5 of 19

Fig. 2: - POPLITEOMENISCAL FASCICLE Consecutive sagittal T2-W fat-suppressed images from lateral to medial showing the normal appearance of posteroinferior popliteomeniscal fascicle (discontinuous white arrow) and postero-superior popliteomeniscal fascicle (thin white arrow). Page 6 of 19

Fig. 3: - POPLITEO-MENISCAL FASCICLE Consecutive sagittal T2-W fat-suppressed images from lateral to medial in 29-year-old man with an acute ACL tear, presenting a partial rupture and thickening of the postero-inferior popliteomeniscal fascicle (thick white arrow), and a complete tear of the postero-superior popliteomeniscal fascicle (thin white arrow). Fig. 4: - DISCOID MENISCUS A) Sagittal T2-W fat- suppressed image through the lateral meniscus shows rectangular slab of meniscal tissue (arrow). B) Coronal T2-W fatsuppressed image of the same patient demonstrates the large rectangular slab of discoid tissue (arrow) Page 7 of 19

Fig. 5: - RING MENISCUS Three consecutive coronal T2-W fat-suppressed images of a 40-year-old man, identifying a triangular shape meniscal tissue (thin white arrow) on the central portion of the lateral compartment, compatible with a ring meniscus. Page 8 of 19

Fig. 6: - RING MENISCUS Central sagittal T1-W image of the same patient, characterizing the internal portion of the ring meniscus (thin white arrow), that could be easily mistaken for a centrally displaced bucket-handle meniscal tear. Fig. 7: - SPECKLED ANTERIOR HORN Consecutive sagittal central PD-W fatsuppressed images showing the interweaving of fibers of the ACL (arrows) with those of the anterior horn of the lateral meniscus determining a spotty hyperintense signal (circle). Page 9 of 19

Fig. 8: - MENISCAL FLOUNCE Sagittal T2-W fat - suppressed MR image through medial femorotibial compartment demonstrates inner border waviness (arrow) of the body of the medial meniscus, without clefts or signal intensity changes Page 10 of 19

Fig. 9: - MENISCAL OSSICLE A)Lateral radiograph of the left knee shows ossicle in the joint compartment (arrow) B)Sagittal T2-W fat- suppressed MR image of the same patient depicts a meniscal ossicle within the substance of the medial meniscus (arrow). Fig. 10: - TRANSVERSE MENISCAL LIGAMENT A) Axial T2-W fat -suppressed images shows the transverse intermeniscal ligament connecting the anterior horns of both menisci B) Sagittal T2-W fat- suppressed weighted image shows the cross section of the transverse meniscal ligament (arrow) as it inserts on the anterior horn of the lateral meniscus. The space between the ligament and meniscus can mimic a tear. Page 11 of 19

Fig. 11: - TRANSVERSE MENISCAL LIGAMENT Several sequential sagittal T2-W fatsuppressed images of the transverse meniscal ligament (arrows ) from medial to lateral connecting the anterior horns of the menisci. The attachment site of this ligament on the meniscus can sometimes mimic a meniscal tear. Page 12 of 19

Fig. 12: - MENISCOFEMORAL LIGAMENTS A)Sagittal T2-W fat- suppressed image demonstrates the meniscofemoral ligament (arrow) running anterior to the PCL (ligament of Humphrey). B)Sagittal T2-W fat- suppressed image demonstrates the meniscofemoral ligament (arrow) running posterior to the PCL (ligament of Wrisberg) Fig. 13: - MENISCOFEMORAL LIGAMENT Coronal T1 -W image shows the longitudinal extent of the posterior meniscofemoral ligament (Wrisberg), as it attaches to the posterior horn of the lateral meniscus (asterisk). The distal aspect of the posterior cruciate ligament is visualized (P). Page 13 of 19

Fig. 14: - THE BUCKET-HANDLE TEAR Sagittal T2-W fat- suppressed MR image shows centrally displaced meniscal fragment (arrow), indicated by the "double PCL sign" which can be mimicked by a prominent anterior meniscofemoral ligament running horizontally, parallel to the PCL. Page 14 of 19

Fig. 15: - WRISBERG RIP Consecutive sagittal T2-W fat-suppressed images from lateral to medial pinpointing a longitudinal vertical tear on the periphery of the lateral meniscus (thin white arrow), that is continuous with the attachment of the meniscofemoral ligament (short thick arrow). Fig. 16: - ANTEROMEDIAL MENISCOFEMORAL LIGAMENT Consecutive axial T2-W fat-saturated images from proximal to distal, presenting the proximal insertion of the anteromedial meniscofemoral ligament (arrows) on the anterolateral wall of the femoral intercondylar fossa, and its distal insertion on the anterior horn of the medial meniscus in a patient with a proximal high grade partial tear of the medial collateral ligament. Page 15 of 19

Fig. 17: - ANTEROMEDIAL MENISCOFEMORAL LIGAMENT Sagittal T2 fat-saturated images identifies the anteromedial meniscofemoral ligament (thin white arrows), following a trajectory immediately anterior to the ACL. Page 16 of 19

Fig. 18: - OBLIQUE MENISCO-MENISCAL LIGAMENT A) Sagittal T2-W fat-suppressed image showing the medial oblique menisco-meniscal ligament (arrow) in the intercondylar notch. B) Coronal T2-W fat-suppressed image showing the medial oblique meniscomeniscal ligament (arrow) in the intercondylar notch. C) Axial T2-W fat-suppressed image showing the medial oblique menisco-meniscal ligament running obliquely through the intercondylar notch. Page 17 of 19

Conclusion MRI is the image method of choice for evaluating internal derangement of the knee, involving the menisci. Radiologists must be familiarized with the wide range of the normal anatomic variants in order to avoid reporting errors and provide accurate diagnosis. Personal information References [1] M. SIMAO and M. NOGUEIRABARBOSA, "Magnetic resonance imaging in the assessment of meniscal anatomic variants and of the perimeniscal ligamentous anatomy: potential interpretation pitfalls," Radiol Bras [online], vol. 44, pp. 117-12, 2011. [2] K. TAN, P. YOONG and A. TOMS, "Normal anatomical variants of the menisci and cruciate ligaments that may mimic disease," Clinical Radiology, vol. 69, pp. 1178-1185, 2014. [3] R. MOHANKUMAR, L. M. WHITE and A. NARAGHI, "Pitfalls and Pearls in MRI of the Knee," American Journal of Roentgenology, vol. 3, pp. 516-530, 2014. [4] M. G. FOX, "MR Imaging of the Meniscus: Review, Current Trends, and Clinical Implications," Magnetic Resonance Imaging Clinics, vol. 15, pp. 103-123. [5] P. TYLER, A. DATIR and A. SAIFUDDIN, "Magnetic resonance imaging of anatomical variations in the knee. Part 1: ligamentous and mmusculotendinous," Skeletal Radiol, vol. 12, pp. 1161-73, 2010. Page 18 of 19

[6] V. F. MUGLIA, M. N. SIMAO and J. a. T. C. S. ELIAS JUNIOR, "Erros comuns de interpretação de ressonância magnética de joelho: como reconhecê-los e evitálos.," Radiol Bras [online], vol. 34, pp. pp. 161-166., 2001. Page 19 of 19