A mother of three suffered 34 separate injuries when she was murdered at a caravan park in Ingoldmells.
Pathologist Dr Stuart Hamilton said that the 64-year-old’s injuries were focused around her head and neck.
The prosecution say that Mrs Treeby was murdered by her partner Andrew Highton while the couple were staying at a caravan park at Ingoldmells to mark her birthday.
She is alleged to have been punched, kicked, stamped on and struck with a glass ashtray.
Dr Hamilton, giving evidence on the fourth day of the trial at Lincoln Crown Court, said that she had extensive bruising and lacerations to the head and face.
Her nose and a bone in her throat were fractured. He told the jury that she had also suffered bleeding on the brain.
He said: “My conclusion is that the cause of death, in this case, has been head injuries.
“There was extensive injury to the head and face entirely in keeping with kicking, stamping and assaults with a blunt object.
“The injuries are in excess of what I would expect to see if they were only punches.
“This has been, in my opinion, a sustained assault focused towards the head and neck area. It was a very sustained assault.
“The nasal bone has been absolutely shattered. That will not occur with a punch.”
The jury has been told that Andrew Highton later admitted assaulting his partner but he claimed she struck him first and that he only delivered “two, three or four punches.”
Andrew Highton, 51, of Highbury Road, Bulwell, Nottingham, denies murder and an alternative charge of manslaughter on 29 May this year.
The trial continues.