Feature Question

(OBQ04-13) A 30-year-old female presents with a painful posterior knee mass. The mass gets larger and more painful with activity. Examination reveals a boggy soft tissue mass about her knee. Radiograph and MRI are shown in Figures A and B. What is the most likely diagnosis? REVIEW TOPIC
FIGURES: A   B        

1. Synovial sarcoma
2. Hemangioma
3. Lipoma
4. Parosteal osteosarcoma
5. Pigmented villonodular synovitis (PVNS)