AN open verdict has been returned on a policewoman who died after suffering a serious head injury while ''playing about'' on a colleague's motorcycle. Constable Cathy Wong Sze-wai, 20, lost control of the bike, did an unintentional ''wheelie'' and was thrown backwards, the inquest heard. She cracked her head on the ground and died a few days later. Two witnesses expressed concern about the treatment Wong received at Queen Mary Hospital, Pokfulam, but Coroner Rodney Venning said: ''There was no direct evidence of a lack of care shown at the hospital.'' Wong spent the evening of May 30 this year with off-duty colleagues. The group met Constable Charles Lo who was patrolling on his Yamaha. Constable Lo, 37, rode his police bike up a spiral staircase to show his friends how it was done. Later they met up again in the car park of the Hong Kong Academy for Performing Arts, Wan Chai. Constable Lo parked his bike but left his key in it. Wong decided to have a go on the bike but lost control almost immediately. She was admitted to hospital in a satisfactory condition and was put under hourly observation. But she suddenly deteriorated and emergency brain surgery failed to save her. Dr Fan Yiu-wah, one of the team who monitored her, said: ''In head injuries, deterioration can set in later than the initial impact, in a delayed manner.'' The coroner told Dr Fan: ''The concern of the family is that could radical intervention at an earlier time have been more successful?'' Dr Fan said Wong's condition did not change right up until she suddenly deteriorated, so there was nothing to do but monitor her up to that point. He added that even had the brain operation succeeded, the chances of survival would not have been very good. When asked about the hospital staff he replied: ''I have confidence in my nursing staff and in their professional abilities.'' Wong's mother and Chief Inspector David Lorimer both expressed concern over her treatment at the hospital, saying Wong did not seem to have received much attention. But the coroner told the jury that it could not bring a lack of care verdict because there was no ''direct evidence'' to suggest this. He added that medical evidence pointed to a ''minimal chance of survival from such an injury''. ''The doctors were satisfied that the management of the patient was appropriate and played no part in her death.'' But Mr Venning added that the concern expressed by the two witnesses about the hospital treatment could lead the jury to being uncertain about a misadventure or accident verdict and could therefore lead to an open verdict. Wong died on June 4 after internal bleeding worsened and her brain began to swell.