Supra-scapular nerve entrapment by ganglion cyst. Value of imaging modalities

Six cases of supra-scapular nerve entrapment by a ganglion cyst within the spino-glenoid notch or developed from the glenoid labrum are reported. Causes of injury or entrapment of the supra-scapular nerve are described including traction or kinking of the nerve, trauma, repetitive exercise, or compression by ganglion cyst. The patients had non specific pain, weakness, and atrophy of the spinatus musculature. Electromyography showed evidence of denervation atrophy. Patients had plain radiographs, arthrography, CT-arthrography, magnetic resonance imaging (MRI) and MR-arthrography. Masses that caused supra-scapular nerve entrapment were well localized and characterized with magnetic resonance imaging, reflecting the superior soft-tissue contrast of this modality. In addition, MRI may demonstrate atrophy of the spinatus muscles. MR-arthrography allows to visualize lesions of the glenoid labrum and in some cases, demonstrates cysts filling. (authors)