The rope ladder: an uncommon artifact and potential pitfall in MR arthrography of the shoulder

MR arthrograms were retrospectively reviewed for susceptibility artifacts induced by accidental injection of a small amount of gas when paramagnetic contrast solution was injected. A pitfall to interpretation, an unusual distribution of intraarticular gas into the sheath of the long biceps tendon that resembled a rope ladder, was observed and compared with findings of bicipital tenosynovitis. Intraarticular gas contamination during MR arthrography must be differentiated from intraarticular loose bodies and findings of bicipital tenosynovitis. Most reliable for the differential diagnosis are the different shapes and sizes of the gas-induced susceptibility artifacts on spin-echo and gradient-recalled echo images.