37 year old male presenting with right shoulder pain

Quadrilateral space syndrome is a clinical syndrome resulting from compression of the axillary nerve and posterior circumflex humeral artery in the quadrilateral space. The quadrilateral space is an anatomic space in the upper arm bounded by the long head of the triceps, the teres minor and teres major muscles, and the cortex of the humerus. On MRI, this syndrome is manifest by focal atrophy involving the teres minor muscle with or without involvement of portions of the deltoid muscle. Fibrous bands in the region of the quadrilateral space are believed to be the cause of nerve and artery compression in most patients with quadrilateral space syndrome. Fibrous bands are usually not visible on MRI. Other causes of quadrilateral space syndrome include trauma, ganglion cyst, paralabral cyst, aneurysms of posterior circumflex humeral artery and tumors in quadrilateral space.