Supralabral air on plain radiography of the shoulder: first sign of an air-containing paralabral cyst.

A forty-one-year-old male patient was referred to our department of Radiology for left shoulder pain and reduced mobility. There was no history of trauma, infection nor therapeutic intervention. A plain radiograph (Fig. A) of the left shoulder showed the presence of two small roundshaped lucent bubbles in the soft tissue above the glenoid. An additional ultrasound examination revealed the presence of a cyst in the suprascapular notch (Fig. B), slight atrophy and increased echogenicity of the infraspinatus muscle. Further investigation with T1 and T2 weighted pulsesequences on MRI revealed a loculated fluid-filled collection in the suprascapular notch, causing an impression on the suprascapular nerve and vessels. This fluid collection contained diminished signal intensity spots caused by the air collections. The infraspinatus muscle, innerved by the suprascapular nerve, showed on T2 weighted MR image a diffuse slightly increased intensity and thickening. Axial T2-weighted MR image (Fig. C) demonstrated communication between the paralabral fluid collection and the glenohumeral joint trough a tear in the superior and posterior glenoid labrum. Based on the imaging findings, the diagnosis of a large locular paralabral cyst, caused by a glenoid labral tear, was made. As a consequence, in this case, the suprascapular nerve was compressed and the infraspinatus muscle showed denervation signs. After arthroscopic decompression of the paralabral cyst, the patient complaints improved.