Meniscal cysts occurs when synovial fluid becomes encysted secondary to a meniscal tear. When they extend beyond the margins of the meninscus they are termed parameniscal cysts.
The frequency of these cysts is also a matter of controversy. In general they are thought to present in ~4-6% of knee MR studies 4.
There are multiple theories regarding the aetiology of meniscal cysts.
Surgical and arthroscopic series report lateral meniscal cysts as a more frequent occurrence as compared to their medial counterparts. Systematic review of MR literature says that frequency of medial and lateral meniscal cysts is almost the same 1. In approximately 4% of cases, meniscal cysts may involve both menisci within the same knee 5.
- while meniscal tears are associated with the vast majority of cysts, anteriorly located lateral parameniscal cysts are less likely to have underlying meniscal tears 9.
- some authors suggest a critical size of a meniscal tear at 12mm along the circumferential axis as identified using MRI, as a discrimination cut off for parameniscal cyst formation 10.
Clinically the patient with meniscal cysts may present with a palpable soft tissue swelling with or without knee pain.
The cysts of medial meniscus usually are along the posterior aspect of posterior horn whereas those of lateral meniscus are along the anterior/anterolateral aspect of the anterior horn or body.
Plain radiographs may show soft tissue swelling at expected locations.
High resolution musculoskeletal ultrasound can be highly sensitive and usually shows the cystic nature of the lesion. It may also demonstrate the associated meniscal tear.
MRI is the investigation of choice for comprehensive imaging of the knee. Many of the cysts are non-palpable and these patients present with knee pain hence MRI can demonstrate the meniscal tear as well as the cyst.
Intracystic signal characteristics include:
- T2: high signal (but often not as high as synovial fluid 4)
- T1 C+ (Gd): no enhancement
MRI may be more sensitive than arthroscopy in detecting cysts since arthroscopic evaluation of the posterior region of the knee joint (posterior to the posterior horn) is limited.
Longstanding large cysts may cause erosions or scalloping of the adjacent bone.
Surgical excision of the cyst can be performed along with repair of the underlying meniscal tear.
- 1. Campbell SE, Sanders TG, Morrison WB. MR imaging of meniscal cysts: incidence, location, and clinical significance. AJR Am J Roentgenol. 2001;177 (2): 409-13. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Sheah K, Png MA. Meniscal cyst causing periarticular tibial erosion. Singapore Med J. 2005;46 (3): 137-9. Singapore Med J (link) - Pubmed citation
- 3.Tschirch FT, Schmid MR, Pfirrmann CW et-al. Prevalence and size of meniscal cysts, ganglionic cysts, synovial cysts of the popliteal space, fluid-filled bursae, and other fluid collections in asymptomatic knees on MR imaging. AJR Am J Roentgenol. 2003;180 (5): 1431-6. AJR Am J Roentgenol (full text) - Pubmed citation
- 4. Helms CA. The meniscus: recent advances in MR imaging of the knee. AJR Am J Roentgenol. 2002;179 (5): 1115-22. AJR Am J Roentgenol (full text) - Pubmed citation
- 5. Anderson JJ, Connor GF, Helms CA. New observations on meniscal cysts. 2010;doi:10.1007/s00256-010-0993-2 - Pubmed citation
- 6. Marra MD, Crema MD, Chung M et-al. MRI features of cystic lesions around the knee. Knee. 2008;15 (6): 423-38. doi:10.1016/j.knee.2008.04.009 - Pubmed citation
- 7. Mccarthy CL, Mcnally EG. The MRI appearance of cystic lesions around the knee. -Skeletal Radiol. 2004;33 (4): 187-209. doi:10.1007/s00256-003-0741-y - Pubmed citation
- 8. Rutten MJ, Collins JM, Van kampen A et-al. Meniscal cysts: detection with high-resolution sonography. AJR Am J Roentgenol. 1998;171 (2): 491-6. AJR Am J Roentgenol (abstract) - Pubmed citation
- 9. De Smet AA, Graf BK, Del Rio AM. Association of parameniscal cysts with underlying meniscal tears as identified on MRI and arthroscopy. AJR Am J Roentgenol. 2011;196 (2): W180-6. doi:10.2214/AJR.10.4754 - Pubmed citation
- 10. Wu CC, Hsu YC, Chiu YC et-al. Parameniscal cyst formation in the knee is associated with meniscal tear size: an MRI study. Knee. 2013;20 (6): 556-61. doi:10.1016/j.knee.2013.03.008 - Pubmed citation
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