This is a classic case of ischiofemoral impingement with a narrowed channel through which the quadratus femoris is positioned.  The muscle acts to externally rotate and adduct the thigh which opens up this channel whereas internal rotation of the hip tends to reduce the space by bringing the lesser trochanter closer to the ischial tuberosity. Note the channel is made even narrower by the additional hamstring tendon origins from the ischial tuberosity.

In this study, the muscle is not only edematous but also attenuated on the PD axial image (just in the channel) indicating the chronicity of impingement.  This is not a neuropathic phenomenon as the whole muscle would be affected.