Rectus femoris sheath: a new localization of hip synovial cyst. 
Iliopsoas bursitis is the classical manifestation of synovial cysts of the hip.  We report the first observation of a new localization of these cysts: the sheath of rectus femoris muscle.  The patient presented with a hip osteoarthritis and an important mass of the front of the thigh.  Computed tomography was useful in establishing the diagnosis and hip arthrography confirmed the communication between the joint and the rectus femoris sheath.