One of Charlie Teo's brain surgeries that left a middle-aged woman in a vegetative state had "no benefit" and the rationale behind it was "nonsense", a disciplinary hearing has been told. 

The committee also heard Dr Teo is accused of slapping a different women across the face in full view of her family, while she was in a coma post surgery.

The controversial Sydney neurosurgeon is facing a week-long disciplinary hearing before the New South Wales Medical Council's Professional Standards Commission, following complaints about two former patients, both of whom died following surgery. 

Two expert witnesses have been called before the hearing to give evidence about whether Dr Teo should have operated on a woman with stage 4 brain cancer in 2018.

The woman, who cannot be identified, had been given 12 to 18 months to live and was "desperate" for Dr Teo to elongate her life.

The woman's husband, who gave evidence on Monday, claims Dr Teo told him the risk of death for a 'radical resection' of her brain tumour would be five per cent. 

Melbourne-based neurosurgeon Andrew Morokoff told the hearing that would be a "falsely low" estimate.

Dr Morokoff was asked whether the risk of severe consequences or death far outweighed any potential benefit of the surgery. 

"Yes, I think so," Dr Morokoff said. 

"Do you see any benefits from a radical resection of this tumour?," Kate Richardson SC said.

"I don't," he said.

The woman died in March 2019 after living in a mostly vegetative state for about six months post surgery.

Dr Teo had allegedly told the family pre-surgery it was important to remove the tumour in the brain stem to prevent a rapid loss of function.

A statement from Amit Goyal, Dr Teo's surgical fellow, explained the rationale for the surgery was to be "aggressive" on one side of the woman's brain.

He said if there was any damage, "likely the other side would be able to compensate for any deficits".

A second neurosurgeon witness, Bryan Stokes AO, called that "nonsense."

He also questioned the time Dr Teo took to complete the surgery, which records show started at 9.12am and finished at 10.55am. 

But Professor Stokes admitted some surgeons were quicker, and it was possible to do the surgery in less than four hours.

"Dr Teo is a very skilled surgeon in my opinion," he said.

The committee has asked to see an MRI taken from the woman's brain immediately after surgery to determine exactly what Dr Teo did, but the scan is missing.

Dr Teo's lawyer told the committee they'd looked but could not find one. 

Dr Teo is also being scrutinised over his decision to operate on a woman in her 60s, who died in late March 2019, about a month after surgery for a brain tumour.

Dr Morokoff told the hearing Dr Teo showed "inappropriate conduct" when he was seen slapping the woman across the face after surgery. 

The expert witnesses said trying to rouse a patient with pain was standard practise but agreed Dr Teo's the method was "totally inappropriate".

"Slapping a patient across the face is actually assault," Professor Stokes said. 

Three neurosurgeons have been shown MRI scans of the woman's brain tumour before surgery. 

While two of the surgeons told the hearing they would not have operated, a third, Paul D'Urso, said a "debulking" operation to reduce the tumour may have helped.

"There's no right or wrong answer about whether you should offer this patient a debulking procedure," he said. 

The hearing was then shown an MRI of the woman's brain after Dr Teo's operation, which showed the surgeon had cut out a large chunk of crucial brain tissue, along with the tumour. 

Professor D'Urso described the operation as "excessive" and would explain why the woman never woke from surgery.

On his way into the hearing, Dr Teo told media some of his surgical peers believed he lied about his results, and were threatened by his skill.

"I think it's a whole lot easier to destroy someone than to upskill," he said.

Dr Teo is due to give evidence on Monday.