Bakers Cysts and Parameniscal Cysts
A Baker’s cyst is a collection of synovial fluid that develops in the posteromedial aspect of the knee. They develop due to intraarticular conditions such as osteoarthritis and meniscal tears. They are not painful but patients often describe a fullness or tightness in the back of the knee that can limit joint mobility and can rarely occlude and compression nearby neurovascular structures, especially with larger cysts. Baker’s Cyst – StatPearls – NCBI Bookshelf
A Parameniscal cyst is a similar condition with the formation of an encapsulated collection of synovial fluid that communicates from the medial or lateral meniscus. They often develop in the young patient due to extrusion of the synovial fluid through a horizontal meniscal tear. The majority of parameniscal cysts are asymptomatic; however, they can grow to become quite large, limiting joint mobility and causing alarm to the patient.
How are they diagnosed?
Locations of the lesions are helpful in narrowing the differential. Imaging is usually requested to confirm the diagnosis. Ultrasound is usually the first-line imaging modality and is often helpful to confirm the diagnosis. On ultrasound they appear as an anechoic, well-defined lesion that may contain internal debris or septae. They will have a ‘neck’ at its deepest extent communicating with the joint space. Diagnostic accuracy of ultrasound for the assessment of Baker’s cysts: a meta-analysis – PubMed
For atypical lesions MRI will be used to confirm the diagnosis and exclude other potential causes
How are they treated?
Treatment is usually reserved for addressing the underlying cause. The most common reasons are osteoarthritis and meniscal tears (please see these sections for more information).
- Specific treatment consists of cystic aspiration and local infiltration with steroid and local anaesthetic under ultrasound guidance. There is a strong likelihood of reoccurrence, but not in all patients, and it can have a profound effect on joint mobility. Ultrasound-guided aspiration and corticosteroid injection of Baker’s cysts in knee osteoarthritis: a prospective observational study – PubMed.
Less commonly, an arthroscopic cystectomy may be considered in certain cases. This is usually in combination with addressing the underlying intraarticular cause. Surgical treatment of popliteal cyst: a systematic review and meta-analysis
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