Hi it may be cysts,bone spur,tumors etc...Cysts about the knee have multiple etiologies, including irritated and inflamed bursae, meniscal cysts caused by intra-articular pathology, and special categories, such the following: Baker cyst or popliteal cyst Ganglia (both intra-articular and extra-articular) Extraneural cysts It is important to realize that other processes can mimic cysts on MRI. Benign and malignant tumors must be ruled out during the workup of any cyst about the knee; other entities to consider are abscesses and vascular masses, such as popliteal vein varices and popliteal artery aneurysms. consult orthopedic surgeon they will do relevant investigations and do the needful