MR Geyser Sign in chronic rotator cuff tears.

Acromio-clavicular (AC) joint cysts are rare presentation of chronic shoulder pathology. These cysts may be observed secondary to either degenerative changes in the AC joint with an intact rotator cuff (type 1 cyst) or following a chronic rotator cuff tear (type 2 cyst). The latter phenomenon is known as Geyser Sign and is described by ultrasound, conventional arthrogram and magnetic resonance imaging (MRI). We present a case of chronic rotator cuff tear presenting with a large type 2 cyst and Geyser Sign on MRI.