From Medical hoax: ‘Cello scrotum’ was just a test tickle.

“Sir, Though I have not come across ‘guitar nipple’ as reported by Dr. P. Curtis, I did once come across a case of ‘cello scrotum’ caused by irritation from the body of the cello. The patient in question was a professional musician and played in rehearsal, practice, or concert for several hours each day. I am, etc., J.M. Murphy.”

Also reported by CNN.