summary Meniscal cysts are a condition characterized by a local collection of synovial fluid within or adjacent to the meniscus most commonly as result of a meniscal tear. Diagnosis is confirmed with MRI studies of the knee. Treatment is generally nonoperative with physical therapy and NSAIDs. Surgical decompression with partial meniscectomy versus meniscus repair may be indicated for persistently symptomatic patients who fail conservative management. Epidemiology Incidence no studies of the general population found in 1-4% of MRI studies of the knee Demographics most commonly associated with a meniscal tear no trend to increased age Anatomic location perimeniscal cysts small lesions of fluid within the meniscus medial cysts are slightly more common than lateral, 2:1 ratio (although literature data are conflicting) medial cysts = posterior horn lateral cysts = anterior horn or mid-portion parameniscal cysts (e.g., baker cysts) extruded fluid outside the meniscus (most common) usually located between semimembranosus and medial head of gastrocnemius Etiology Pathophysiology mechanism of injury meniscal tear functions as a one-way valve synovial fluid extrudes and then concentrates to form gel-like material pathoanatomy horizontal and complex tears, usually = parameniscal cysts radial or vertical tears, usually = perimeniscal cysts Associated conditions articular cartilage injury anterior cruciate ligament tear Anatomy Meniscus composition fibroelastic cartilage interlacing network of collagen, proteoglycan, glycoproteins, and cellular elements composed of 65-75% water Collagen 90 % Type I collagen shape medial meniscus stretched-out, C-shape with triangular cross section lateral meniscus more circular in shape covers larger area of articular surface Blood supply medial inferior genicular artery supplies peripheral 20-30% of medial meniscus lateral inferior genicular artery supplies peripheral 10-25% of lateral meniscus synovial fluid central 75% of meniscus' receive nutrition through diffusion Presentation History may have recent trauma Symptoms asymptomatic pain localized to medial/lateral joint line or back of knee mechanical symptoms locking and clicking delayed or intermittent knee swelling weakness or claudication (neaurovascular impingement) Examination inspection popliteal mass best visualized with the knee in extension palpation joint line tenderness palpable mass motion crepitus Imaging Radiographs should be normal in young patients with an acute meniscal injury or cyst MRI indications MRI is most sensitive diagnostic test for meniscal cyst and meniscal tear findings cyst with bright T2 signal necrotic tissue, nerve sheath tissue, and pus can all resemble cysts on T2-weighted MRIs IV contrast enhancement may be needed Treatment Non-operative rest, NSAIDS, rehabilitation indications indicated as first line of treatment for small perimeniscal cysts and parameniscal cysts outcomes trial of medical therapy to observe patients pain response may be effective in population with degenerative tears aspiration and steroid injection indication isolated baker's cysts in young patient technique cyst drainage ultrasound guided injection into the cyst outcomes poor outcomes in older degenerative mensical tears with associated cysts Operative arthroscopic debridement, cyst decompression and meniscal resection indications perimeniscal cysts with an associated tear that is not amenable to repair (e.g., complex, degenerative, radial tear patterns) technique decompress cyst completely perform partial meniscectomy outcomes incomplete meniscal resection may lead to recurrence cyst excision using open posterior approach indications symptomatic parameniscal cysts outcomes incomplete resection may lead to recurrence Technique Cyst excision using open posterior approach patient prone curved incision over popliteal fossa interval between medial head of gastrocnemius and semimembranosus sharp dissection of cyst margins to joint capsule