Cysts and cyst-like lesions around the knee: ultrasonographic and magnetic resonance imaging correlation

Cystic lesions are common around the knee joint. They include joint recesses, arthrosynovial cysts, gan -glion cysts, bursae, and cystic tumors. The clinical presentation is predominantly determined by lesion location, volume, and mass effect on adjacent structures. Cysts are easily detected on both ultrasound (US) and magnetic resonance imaging (MRI). Most superficially located cystic lesions around the knee can be confidently characterized using Doppler US without the need for further imaging. US can also guide cyst aspiration or therapeutic injection of corticosteroids and local anesthetics. MRI may be helpful for delin-eating complex anatomy and is particularly useful for evaluating deeply located cystic masses and intraos-seous cysts. Certain benign and malignant masses exhibit high signal intensity on T2-weighted images and can mimic true cysts. Whenever there is doubt about the cystic nature of a visualized mass, administration of a contrast agent is mandatory to rule out solid tumors with cystic degeneration or myxoid contents.