A former paramedic is seeking compensation and an investigation by the General Medical Council after part of his brain was removed in error by an NHS surgeon.
John Tunney, from Sutton Coldfield, Birmingham, suffered a haemorrhage and permanent brain injuries after he was subjected to unnecessary brain surgery, lawyers Irwin Mitchell said.
Mr Tunney (63) underwent a biopsy in 2008 after scans showed a tumour in his pituitary gland.
During the procedure at Coventry's Walsgrave Hospital a surgeon wrongly removed healthy brain tissue rather than the tumour, lawyers said.
Mr Tunney, who used to work for West Midlands Ambulance Service, was left partially sighted and in need of constant supervision and support.
Timothy Deeming, from Irwin Mitchell, described the blunder as "appalling" and said the tumour was found to be benign and could have been controlled with medication if blood test results had been reviewed before the biopsy.
He said: "The fact that the surgeon managed to remove perfectly healthy tissue rather than a sample of the tumour tissue is an appaling error. To then find the procedure was totally unnecessary because clinicians had failed to review a blood test, really does add insult to injury."
University Hospitals Coventry and Warwickshire NHS Trust has admitted liability and apologised to Mr Tunney.