Sonography of pigmented villonodular synovitis in the ankle joint.

Pigmented villonodular synovitis is a benign proliferative disorder of the synovium that results in villous nodule formation in joints, tendon sheaths, and bursae. We present a case of pigmented villonodular synovitis of the ankle joint that was diagnosed by sonography with color Doppler imaging. The sonograms revealed hypoechoic synovial proliferation, and hypervascularity was visible on color Doppler images. The differential diagnosis of a synovial thickening or mass is also discussed.