Sunita Dhanda and Swee Tian Quek
Pigmented villonodular synovitis is a benign proliferative synovial disorder of unknown origin that may affect the joints, bursae, or tendon sheaths, most frequently the knee. It can occur in diffuse or focal form. MR imaging is routinely used for diagnosis and follow-up in patients with pigmented villonodular synovitis. The lesions show hemosiderin deposition due to their tendency to bleed and a characteristic hypointense signal with all pulse sequences, an important diagnostic feature on MRI which helps in making the diagnosis in a young adult with monarticular involvement by synovial soft tissue mass without calcifications, with preserved joint space and normal juxtarticular bones.