Cystic entrapment of infraspinatus branch of suprascapular nerve is a rare cause of shoulder pain with infraspinatus atrophy. We discuss the ultrasonographic diagnosis and ultrasonography- guided aspiration of the cyst as a treatment.

Case: A 37-year-old, ship-yard laborer had experienced left shoulder discomfort and pain without trauma history. Physical examination showed profound selective atrophy of left infraspinatus muscle. Simple X-ray of shoulder showed normal findings. Electrodiagnostic examination revealed delayed motor latency of infraspinatus branch of suprascapular nerve and denervation potentials of infraspinatus muscle exclusively. Ultrasonographic finding showed 13.5⁓21.5 mm sized cystic mass around left infraspinatus notch. Ultrasonography-guided aspiration was done, and then electrical stimulation therapy and strengthening exercise of left shoulder were performed. Symptoms were improved.

We report a rare case of cystic entrapment of infraspinatus branch of suprascapular nerve in a patient without traumatic insult.