Parameniscal Cyst

Parameniscal Cyst

KEY FACTS

Imaging

• Cystic mass in continuity with horizontal meniscal tear
- Medial parameniscal cyst slightly more common than lateral parameniscal cyst
• Meniscal tear forces synovial fluid or mucoid content into parameniscal cyst
• Cyst is usually well defined and filled with anechoic or hypoechoic gelatinous-type fluid
- Meniscal tear does not always have to be present
  - – Tear may have healed
- Especially with anterior horn lateral meniscus
• Cyst may lie in direct continuity with meniscus or connect via serpiginous connecting stalk
• Colloid content of parameniscal cyst similar to that of ganglia and Baker cyst
- Diagnosis of parameniscal cyst relies on showing continuity between cyst and meniscus
• Check for pericystic soft tissue inflammation
• Parameniscal cysts, especially medially, can be very large
• Comment on cyst size, loculation, extent, associated meniscal tear, recent cyst leakage ± localized inflammation
- MR to assess meniscal tear
- Intracapsular parameniscal cysts may not be visible on US
• US-guided aspiration ± hyaluronidase injection ± steroid injection
- Provides temporary and often long-term symptom relief
  - – Especially for smaller cysts and poor surgical candidates

Diagnostic Checklist

• Not every paraarticular cyst with pedicle extending to knee joint is parameniscal cyst
- Need to distinguish from paraarticular ganglion
• Inflammation around parameniscal cyst usually results from recent leakage or extension
- Leakage common cause of symptom exacerbation

Clinical photo shows moderate swelling on the medial aspect of the knee around the medial joint line due to a parameniscal cyst.

Clinical photo shows moderate swelling on the medial aspect of the knee around the medial joint line due to a parameniscal cyst.

Longitudinal US of the medial aspect of the knee shows a large parameniscal cyst located superficial to the medial collateral ligament . The cyst is extending proximally toward the knee joint.

Longitudinal US of the medial aspect of the knee shows a large parameniscal cyst located superficial to the medial collateral ligament . The cyst is extending proximally toward the knee joint.

Longitudinal US just proximal to the previous image shows a thin tract extending through the medial collateral ligament toward the periphery of the thinned degenerate medial meniscus .

Longitudinal US just proximal to the previous image shows a thin tract extending through the medial collateral ligament toward the periphery of the thinned degenerate medial meniscus .

Graphic shows horizontal meniscal tear (“fish mouth” tear) , with meniscal mucoid degeneration and a small parameniscal cyst arising from the peripheral aspect of the tear. Meniscal tears are much better depicted on MR than US.

Graphic shows horizontal meniscal tear (“fish mouth” tear) , with meniscal mucoid degeneration and a small parameniscal cyst arising from the peripheral aspect of the tear. Meniscal tears are much better depicted on MR than US.

TERMINOLOGY

Synonyms

• Meniscal cyst
- This term should be reserved for intrameniscal cysts

Definitions

• Cyst extending from meniscal tear
- Usually horizontal tear (most common) or complex tear (2nd most common)

IMAGING

General Features

• Best diagnostic clue
- Cystic mass in continuity with horizontal meniscal tear
• Location
- Can arise from any part of meniscus
  - – Medial meniscus (~ 60%), lateral meniscus (~ 40%)
- Most common locations
  - – Junction between body and posterior horn medial meniscus (posterior to medial collateral ligament)
  - – Junction between body and anterior horn lateral meniscus (anterior to lateral collateral ligament)
• Size
- Tiny (few mm) to large extraarticular cyst (> 10 cm)
• Morphology

MR Findings

• T1WI
- Hypointense cyst mass
- If proteinaceous, cyst may be iso- or hyperintense
• T2WI
- Rounded, hyperintense mass
  - – Lobulation and septation
- Tear = linear hyperintense meniscal signal extending to articular surface
  - – Peripheral meniscal tear may not visibly connect with meniscal articular surface (noncommunicating tear)

Ultrasonographic Findings

• Parameniscal cyst ± extraarticular component with communicating stalk
- Meniscal tear does not always have to be present, especially from anterior horn of lateral meniscus
• Meniscus is seen as diffusely echogenic, sharply defined structure within medial and lateral femorotibial compartments
- Medial meniscus easier to see on US
  - – Only peripheral part of menisci can be seen on US
- Body of menisci is best seen with limited views of other areas
• Meniscal tear = linear or wedge-shaped hypoechogenicity within meniscus extending to meniscal periphery
- Be careful because normal meniscus can mimic appearances of horizontal tear
- Extrusion of medial meniscal body is common accompanying feature
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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

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