The diagnosis is based on characteristic swelling behind the knee and your doctor can aspirate the mass (place a needle in it) and withdraw characteristic fluid to confirm the diagnosis. There are non-invasive tests as well. An ultrasound will show the characteristic sac that supports the diagnosis. If necessary, an arthroscopic procedure may be done to remove the cyst and aspirate the area around it. Sometimes a Baker's Cyst will go away without treatment.
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