Intramuscular ganglion arising from the acromioclavicular joint.

We report a case of a 80-year-old White woman presenting with a localized painless swelling in the upper parascapular region of the right shoulder. Ultrasound (US) showed a ganglion arising from the acromioclavicular joint (ACJ) and extending inside the trapezius muscle, together with a massive tear of the rotator cuff (RC). Magnetic resonance imaging (MRI) confirmed the US findings. Ganglia arising from the ACJ are rare and usually associated with massive RC tears. Their intramuscular extension, to the best of our knowledge, has never been reported in the radiological literature and can mimic a tumor.