What was supposed to be a routine surgical procedure for Joan Rivers went wrong when a doctor who arrived at the clinic with the comedian’s entourage performed an unplanned biopsy on her vocal cords, a medical source who was briefed on the case told the New York Daily News. That biopsy caused Rivers’s vocal cords to seize, cutting off her air supply, the source told the newspaper. Rivers, who was 81, was rushed to a hospital, where she eventually died. The biopsy is the kind of procedure that should not have been performed outside of a hospital, medical experts told the newspaper. The comedian and TV host had the procedure Aug. 28 at Yorkville Endoscopy in New York City. She had signed off only on the endoscopy and not the biopsy, the source told the paper. The Daily News said a Rivers representative declined to comment, and that a Yorkville spokeswoman said she could not comment because of confidentiality laws.