US actress Joan Rivers died from cerebral damage caused by lack of oxygen in her blood, a "predictable complication" during a medical procedure, the New York Chief Medical Examiner's Office has announced.

The popular comedienne, performer and TV host died in New York Sep 4, a week after undergoing a minor throat operation that required her to be admitted on an urgent basis to Mount Sinai Hospital.

The medical examiner's office said Thursday that Rivers was anesthetised with Propofol -- which was also implicated in the death of Michael Jackson -- during a procedure to try and repair damage to her vocal cords.

The actress's personal physician is at the centre of the investigation after supposedly performing a biopsy on Rivers' vocal cords for which he did not have the patient's signed authorisation or the hospital's permission, several US media outlets have reported.

The medical examiner's report, however, does not assign any negligence in the matter and calls Rivers's death a "therapeutic complication".

Rivers, 81, got her start in television in 1965 as a writer for "The Tonight Show", obtained her own TV show, "The Joan Rivers Show", in 1993 and in recent years had hosted "Fashion Police".