The CEO of Windsor Regional Hospital says he failed a healthy patient who underwent a lumpectomy and had her lymph nodes removed.

David Musyj said he is ultimately responsible for the mistake in Windsor Regional Hospital's pathology department that led to the unnecessary procedures performed at Hotel-Dieu Grace by Dr. Barbara Heartwell, who in 2009 unnecessarily removed a healthy breast from a woman.

That mistaken mastectomy led to a $2.2-million lawsuit and a health ministry review.

In the latest error, the pathology department mixed up the test results of the healthy woman with those of a woman diagnosed with advanced stage breast cancer.

Hospital staff notified the patient of the mistake Wednesday.

“As CEO, I’m the one responsible if policies and procedures are not followed. This occurred under my watch. I’m responsible, this is not on the surgeon,” said CEO David Musyj. “What we are dealing with here is an unfortunate administrative error made in our pathology department where existing practices and procedures were not followed.

“If they were followed, this would not have happened.”

Musyj said the pathologist who made the administrative error has voluntarily taken paid time off. He called the pathologist "a good worker with no history" and said the pathologist is "remorseful and distraught."

The hospital is investigating exactly what went wrong and how, Musyj said.

Windsor Regional's chief of pathology, Dr. David Shum, said more than one case was open at a time and that is how the mix-up occurred.

Shum said the checks and balances in place focus on the correct diagnosis and not the correct patients. He said 10 or 11 pathologists at Windsor Regional handle 30,000 surgical cases each year.

Musyj said the hospital is helping the patient with medical treatment. He said he is not sure whether the woman is taking legal action.

Windsor Regional's chief of staff, Dr. Gary Ing, said the generally accepted universal standard for minor discordance in pathology overall is 10 per cent. He added that pathology "is not exact."

"We have one and it is not acceptable," Ing said. "People expect the best from us ... we have to have high standards. But we are human."

Not the first mistaken surgery

In 2009, Heartwell misread a pre-surgery pathology report that ruled a lump in a woman's breast was benign.

Hospital officials said the woman was initially told she had breast cancer and underwent a single mastectomy in the fall of 2009.

A release issued by the hospital said that after misreading the report, Heartwell, a surgeon with 28 years' experience, "unfortunately proceeded with the surgery."

While investigating that incident, the hospital learned that Heartwell performed a mastectomy in 2001 on a patient who also did not have cancer.

In late 2009, Heartwell voluntarily stopped operating. She later asked to have her operating privileges restored, but the hospital put her on suspension instead.

The board of directors at Hôtel-Dieu Grace Hospital reinstated Heartwell's operating privileges in March 2011.

Veteran pathologist Dr. Olive Williams resigned after the provincial health ministry reviewed thousands of files and accused her of making numerous errors.

The Heartwell cases and investigations led to the health ministry making several recommendations to change procedures to ensure mistakes would never happened again.