Discoid Meniscus PDF

# Discoid Meniscus ## Terminology **Abbreviations and Synonyms** * Discoid meniscus (DM) **Definitions** * Large, congenitally dysplastic meniscus with loss of normal semilunar shape * Result of failure of resorption of central portion ## Imaging Findings **General Features** * Best diagnos...

# Discoid Meniscus ## Terminology **Abbreviations and Synonyms** * Discoid meniscus (DM) **Definitions** * Large, congenitally dysplastic meniscus with loss of normal semilunar shape * Result of failure of resorption of central portion ## Imaging Findings **General Features** * Best diagnostic clue: Large meniscus with loss of normal semilunar shape filling lateral or medial compartment (50% or greater coverage of lateral tibial plateau) on sagittal and coronal images * Location: * Lateral discoid meniscus is more common than medial discoid meniscus * Can be bilateral * Size: > 13 mm * Morphology: * Pancake shaped meniscus with intact central portion * Large but incomplete disc commonly seen **Radiographic Findings** * Radiography: * Widening of joint space with hypoplastic femoral condyle and high fibular head in lateral discoid meniscus * Cupping of lateral tibial plateau **MR Findings** * **T1WI:** * Meniscal size > 13 mm in cross section * Normal hypointense meniscus is 5-13 mm from the capsular margin to the free edge on a central coronal image * Discoid meniscus exhibits continuous body segment appearance on ≥ 3 consecutive sagittal 4-5 mm thick images * **T2WI:** * Meniscus is hypointense * Intrameniscal mucoid degeneration or cyst may be intermediate to hyperintense on T2* GRE or FS PD FSE * Uniformly hypointense large meniscus * Mucinous degeneration and intrameniscal cystic cavities are hyperintense * Tear as hyperintense signal * Horizontal tear morphology common * Discoid meniscus is larger and disc shaped, filling a greater surface area of the central compartment * Tear is seen as hyperintense signal (T1, PD, GRE T2*) ## Differential Diagnoses * **Flipped Meniscus:** * Seen on all short TE sequences * Complete discoid meniscus has "pancake" appearance * Extending from intercondylar notch to the periphery of compartment * On MR arthrography: contrast extends into discoid meniscal tear * **Bucket-Handle Tear** ## Key Facts * **Pathology:** * Etiology: Failure of resorption of the central portion of meniscus * Microscopically normal meniscus * **Clinical Issues:** * Patients often present with pain, clicking and snapping * Often asymptomatic in children * **Diagnostic Checklist:** * Identify the number of images with meniscus body segment visualized, if more than three consider DM * Absent clear space at center of weightbearing surface of lateral compartment ## Staging, Grading or Classification Criteria * Watanabe classification: * **Complete:** Discoid meniscus extending into the intercondylar notch on coronal images * **Incomplete:** Partial discoid morphology +/- extension toward the intercondylar notch on coronal images * **Wrisberg-ligament type:** Lacks posterolateral meniscotibial attachment * Classification by surface configuration - associated tear patterns (arthroscopic): * **Vertical:** * Longitudinal tear (primary tear pattern is in vertical plane) * Flap tear (primary tear pattern is in vertical plane) * Radial tear * **Horizontal:** * Horizontal cleavage tear * Longitudinal tear (primary tear pattern is in horizontal plane) * Flap tear (primary tear pattern is in horizontal plane) ## Clinical Issues * **Presentation:** * Most common signs/symptoms: pain, clicking and snapping * Often asymptomatic in children * Locking is a common presentation in children * Symptoms may not develop until adolescence of young adulthood * Bilaterality: 20-90% * Click or clunk at the joint line during terminal 15-20 degrees of extension * **Demographics:** * **Age:** * Children asymptomatic * Adults usually symptomatic * **Gender:** No predilection * **Natural History & Prognosis:** * Extension loss * Snapping (Wrisberg type) * Giving way * Palpable joint line mass * Progression to a meniscal tear * Painful intrameniscal cystic cavities of mucinous degeneration * **Treatment:** * Conservative initially * Partial meniscectomy * Saucerization/partial resection of the discoid portion to create a more normal shaped meniscus ## Diagnostic Checklist * Consider: Displaced flap tear/bucket-handle tear as differential diagnosis * **Image Interpretation Pearls:** * Identify the number of images with meniscus body segment visualized, if more than three consider DM * Absent clear space at center of weightbearing surface of lateral compartment * Less common involvement of medial compartment ## Selected References 1. Samoto N et al: Diagnosis of discoid lateral meniscus of the knee on MR imaging. Magn Reson Imaging 20(1):59-64, 2002 2. Choi NH et al: Medial and lateral discoid meniscus in the same knee. Arthroscopy 17(2):E9, 2001 3. Rao PS et al: Clinical, radiologic, and arthroscopic assessment of discoid lateral meniscus. Arthroscopy 17(3):275-7, 2001 4. Rohren EM et al: Discoid lateral meniscus and the frequency of meniscal tears. Skeletal Radiol 30(6):316-20, 2001 5. Arnold MP et al: Symptomatic ring-shaped lateral meniscus. Arthroscopy 16(8):852-4, 2000 6. Araki Y et al: MR imaging of meniscal tears with discoid lateral meniscus. Eur J Radiol 27(2):153-60, 1998 7. Raber DA et al: Discoid lateral meniscus in children. Long-term follow-up after total meniscectomy. Bone J Joint Surg 80(11):1579-86, 1998 8. Ryu KN et al: MR imaging of tears of discoid lateral menisci. AJR 171(4):963-7, 1998 9. Maffulli N et al: Knee arthroscopy in Chinese children and adolescents: An eight-year prospective study. Arthroscopy 13(1):18-23, 1997 10. Connolly B et al: Discoid meniscus in children: Magnetic resonance imaging characteristics. Canadian Association of Radiologists Journal 47(5):347-54, 1996 11. Washington ER et al: Discoid lateral meniscuc in children. Long-term follow-up after excision. Bone J Joint Surg 77(9):1357-61, 1995 12. Pellacci F et al: Lateral discoid meniscus: Treatment and results. Arthroscopy 8(4):526-30, 1992 13. Aichroth PM et al: Congenital discoid lateral meniscus in children. A follow-up study and evolution of management. Bone J Joint Surg 73(6):932-6, 1991 14. Fritschy D et al: Discoid lateral meniscus. International Orthopaedics 15(2):145-7, 1991 15. Sugawara O et al: Problems with repeated arthroscopic surgery in the discoid meniscus. Arthroscopy 7(1):68-71, 1991 16. Dimakopoulos P et al: Partial excision of discoid meniscus. Arthroscopic operation of 10 patients. Acta Orthopaedica Scandinavica 61(1):40-1, 1990 17. Bellier G et al: Lateral discoid menisci in children. Arthroscopy 5(1):52-6, 1989 18. Vandermeer RD et al: Arthroscopic treatment of the discoid meniscus: Results of long-term follow-up. Arthroscopy 5(2):101-9, 1989 19. Hayashi LK et al: Arthroscopic meniscectomy for discoid lateral meniscus in children. Bone J Joint Surg 70(10):1495-500, 1988 20. Dickhaut SD et al: The discoid lasteral-meniscus syndrome. J Bone Joint Surg 64:1068-73, 1982 ## Image Gallery * **Typical:** * (Left) Sagittal FS PD FSE MR shows a discoid lateral meniscus. Meniscal tissue that is continuous with the anterior and posterior horn throughout multiple sagittal images is characteristic. * (Right) Coronal PD FSE MR shows a discoid lateral meniscus. * **Variant:** * (Left) Sagittal FS PD FSE MR shows a torn and degenerated discoid lateral meniscus (arrow). * (Right) Coronal FS PD FSE MR shows a torn and degenerated discoid lateral meniscus (arrow). * **Variant:** * (Left) Axial oblique graphic shows a large lateral meniscus that is discoid-like. * (Right) Coronal PD FSE MR shows a large, discoid-like lateral meniscus # Meniscal Degeneration ## Terminology **Abbreviations and Synonyms** * Meniscal grade 1 and meniscal grade 2 signal intensity = meniscal degeneration, intrasubstance signal, intrasubstance degeneration **Definitions** * Internal degeneration of meniscal fibrocartilage resulting from chronic shear stresses + axial loading * Caused by rotation, flexion & extension of knee during normal walking as well as cumulative effects of traumatic injuries of knee ## Imaging Findings **General Features** * Best diagnostic clue: Increased signal intensity within meniscal substance on short TE MR images not extending to articular surface * Location: Can occur in either meniscus but most common in posterior horn of medial meniscus * Size: Variable from focal area to linear distribution - extending from capsular periphery * Morphology: * Nonarticular focal or globular intrasubstance increased signal intensity (grade 1 signal) * Horizontal linear intrasubstance increased signal intensity (grade 2 signal) **MR Findings** * **T1WI:** * T1WI & short TE images are sensitive to meniscal degeneration * Short TE sequences: T1, PD, T2* GRE * **T2WI:** * Moderate to extensive lesions demonstrate mild increased signal intensity on T2WI * Intrameniscal degenerative cyst detection: Increased signal intensity (fluid) on T2WI * Increased signal intensity: * Globular * Linear * Within the substance of the meniscus * **MR arthrography:** * Arthrography does not show communication with an articular surface of the meniscus ## Differential Diagnoses * **Meniscus Vessels** * **Meniscus Vessels** * **Meniscal Ossicle** ## Key Facts * **Intrameniscal Tear not Communicating with an Articular Surface** * **Pathology:** Common meniscal abnormality * **Epidemiology:** * **Clinical Issues:** * Typically asymptomatic * Symptoms are suggestive of meniscal tear/intrameniscal closed tear * Clinical profile: May present with pain without typical signs of clicking * Meniscal degeneration may be underestimated on FSE images secondary to blurring effect with increased echo spacing ## Pathology **General Features** * General path comments: May be mimicked in young person by prominent, linear vascularity in plane of middle perforating collagen bundle * Etiology: * Internal degeneration of the meniscal substance resulting from chronic stresses (abnormal shear forces) caused by * Rotation, flexion and extension of knee during normal walking * Cumulative effects of traumatic injuries of the knee * Epidemiology: Common meniscal abnormality **Gross Pathologic & Surgical Features** * Pale, often mucinous regions of discoloration in a variety of patterns within meniscal substance * No tear identified **Microscopic Features** * Mucinous degeneration and chondrocyte deficient regions * Pale staining with hematoxylin and eosin (H&E) * Increased production of mucopolysaccharide ground substance * Myxoid, mucinous or hyaline degeneration * May have linear appearance (grade 2 degeneration) * Microscopic clefting and collagen fragmentation may be seen in hypocellular regions of the fibrocartilaginous matrix * Central (middle) perforating bundle of the meniscus is a horizontal buffer zone between the different frictional forces * Between the femur and tibia is a preferential site for accumulation of mucinous ground substance (degeneration) * Common location for the development of grade 2 signal intensity ## Staging, Grading or Classification Criteria * **Grading of meniscal signal:** * **Grade 1:** Nonarticular, focal or globular increased signal intensity within the meniscal substance on short TE sequences * **Grade 2:** Horizontal, linear increased signal intensity within the meniscal substance on short TE sequences * Extending from the capsular periphery of the meniscus but not extending to an articular surface * Histologically usually more extensive degeneration than that seen with MRI grade 1 * **Grade 3:** Increased signal intensity that communicates or extends to at least one articular surface of the meniscus * Represents a meniscal tear with fibrocartilaginous separation * **Classification based on location - vascular zones:** * **White zone (white/white zone):** Completely avascular central portion of the meniscus including inner one third. Menisci debrided. * **Red-white junction (red/white zone):** Middle third between free edge and peripheral third. Incompletely vascularized area. Debridement vs. repair. Repair especially if vascular pedicle can be established. * **Red zone (red/red zone):** Peripheral one third. Vascularized area. Primary repair usually possible if tear confined to red/red zone or peripheral portion of red/white zone. ## Clinical Issues * **Presentation:** * Most common signs/symptoms: typically asymptomatic. Symptoms are suggestive of meniscal tear/intrameniscal closed tear. * Clinical profile: May present with pain without typical signs of clicking. * If symptomatic with meniscal grade 2 signal, the findings may represent an intrameniscal closed tear. A closed tear is associated with grade 3 signal intensity which weakens as it approaches an articular surface of the meniscus. * **Demographics:** * Age: Typically older patient. Also seen in younger, active patients. * Gender: No predilection. * **Natural History & Prognosis:** * May progress to tear, especially horizontal cleavage tear when in the posterior horn of the medial meniscus. * Does not necessarily indicate that a tear will occur. * Mucinous degeneration does represent potential structural weakening within the meniscus. * **Treatment:** * Conservative: Meniscal degeneration is treated conservatively. * Surgical: None for pure degeneration. ## Diagnostic Checklist * Consider: Vascularity in a young person. * **Image Interpretation Pearls:** * Use short TE sequences especially if fluid signal is present within the meniscus. * T2* GRE images sensitive for intrasubstance degeneration. * Meniscal degeneration may be underestimated on FSE images secondary to blurring effect with increased echo spacing. * Blurring seen with shorter effective TE, a longer echo train length & a lower acquisition matrix. ## Selected References 1. Anderson MW: MR imaging of the meniscus. Radiol Clin North Am 40(5):1081-94, 2002 2. Fukuta SK et al: Prevalence of abnormal findings in magnetic resonance images of asymptomatic knees. J Orthop Sci 7(3):287-91, 2002 3. Greis PE et al: Meniscal injury: Management. J Am Acad Orthop Surg 10(3):177-87, 2002 4. Nawata K et al: Magnetic resonance imaging of meniscal degeneration in torn menisci: A comparison between anterior cruciate ligament deficient knees and stable knees. Knee Surg Sports Traumatol Arthrosc 7(5):274-7, 1999 5. Crues JV III: The impact of MRI on our understanding of the pathology of sports injuries. Sportverletz Sportschaden 8(4):156-9, 1994 6. Peterfy CG et al: "Magic-angle" phenomenon: A cause of increased signal in the normal lateral meniscus on short-TE MR images of the knee. AJR 163(1):149-54, 1994 7. Raunest J et al: Magnetic resonance imaging (MRI) and arthroscopy in the detection of meniscal degenerations: Correlation of arthroscopy and MRI with histology findings. Arthroscopy 10(6):634-40, 1994 8. Stoller DW et al: Meniscal tears: Pathologic correlation with MR imaging. Radiology 163(3):731-5, 1987 ## Image Gallery * **Typical** * (Left) Sagittal graphic shows linear intrasubstance degeneration (grade 2 degeneration). * (Right) Sagittal PD FSE MR shows linear grade 2 intrameniscal degeneration (arrow). * **Variant** * (Left) Coronal PD FSE MR shows diffuse intrameniscal degeneration (arrow) of the posterior horn of the medial meniscus adjacent to a radial tear of the posterior horn root attachment. There is slight enlargement of the degenerated posterior horn. * (Right) Coronal PD FSE MR shows grade 2 intrameniscal degeneration of the lateral meniscus body and grade 1 intrameniscal degeneration of the medial meniscus body. * **Typical** * (Left) Sagittal graphic shows free edge fraying. * (Right) Sagittal PD FSE MR shows increased signal (arrow) within the free edge of the medial meniscus confirmed at arthroscopy as free edge fraying.