Paralabral cyst: an unusual cause of quadrilateral space syndrome.

A paralabral cyst arising from a detached inferior glenoid labral tear was shown by magnetic resonance imaging (MRI) to dissect into the quadrilateral space, resulting in a compressive neuropathy of the axillary nerve. Three consecutive MRI examinations were performed over a 5-year period in a 47-year-old man with a long history of worsening shoulder pain. The MRI examinations revealed a slowly enlarging paralabral cyst extending into the quadrilateral space with progressive atrophy of the teres minor muscle.