Magnetic resonance images of fingers: psoriatic arthritis. Shown are T1-weighted (a) precontrast and (b) postcontrast coronal magnetic resonance images of the fingers in a patient with psoriatic arthritis. Enhancement of the synovial membrane at the third and fourth proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints is seen, indicating active synovitis (large arrows). There is joint space narrowing with bone proliferation at the third PIP joint and erosions are present at the fourth DIP joint (white circle). Extracapsular enhancement (small arrows) is seen medial to the third and fourth PIP joints, indicating probable enthesitis. Note that this particular slice does not allow optimal visualization of all of the mentioned pathologies.