PARAMENISCAL CYST

PDFS SAGITTAL IMAGE SHOWING LATERAL MENISCAL TEAR

PDFS SAGITTAL IMAGE SHOWING PARAMENISCAL CYST

STIR CORONAL IMAGE SHOWING TEAR IN LATERAL MENISCUS AND PARAMENISCAL CYST

STIR CORONAL IMAGE SHOWING PARAMENISCAL CYST

AXIAL GRE IMAGE SHOWING PARAMENISCAL CYST.

MENISCAL AND PARAMENISCAL CYSTS:

HOW THEY ARE FORMED?

• They are usually formed as a sequel to trauma or degeneration which inititaes necrosis near the peripheral margin of the meniscus leading to mucoid degeneration and softening of the meniscal collagenous tissue with local accumulation of synovial fluid. 
• More often, this fluid extends to the meniscocapsular margin thorugh the meniscal tear displacing the capsule peripherally and thereby forms a paramenical cyst in the surrounding tissues.
•  Rarely, fluid accumulates locally within the meniscal tear and is contained within the meniscus.

IMAGING:

• On MR, intrameniscal cysts are seen as small fluid pockets within the meniscus. Adjacent horizontal cleavage tear may or may not be seen.
• Parameniscal cysts are seen as well defined ( often septated) fluid collections in continuity with horizontal cleavage tears or complex meniscal tears with horizontal component.
• They are usually hyperintense on all fluid sensitive sequences. However, cyst may show low signal sometimes on T2, either due to dessication or hemorrhage.
• If large, parameniscal cysts may cause bony erosion.

LOCATION:
-Medial> Lateral
-Most common site is along posteromedial aspect of medial meniscus
-Lateral meniscus cysts more commonly arise from its anterior and mid portions
-Although, medial meniscal cysts are more common, lateral meniscal cysts are picked up more often clinically.
-Lateral cysts are better defined and tend to remain close to the joint margin.
-Medial meniscal cysts are more tightly bound to the medial collateral ligament and hence, fluid accumulation is usually some distance away from the meniscal tear. However, a thin connecting stalk is usually seen between the cyst and meniscal tear.

DIFFERENTIAL DIAGNOSIS: It is very important to see the associated meniscal tear with connection to the cyst.

• Semimembranosus/ Pes anserine bursitis
• MCL bursitis

 REFERENCE:

•  McCarthy CL, McNathy: The MRI appearance of cystic lesions around the knee.Skeletal Radiol. 33:187-209, 2004.