The file stated that the woman, identified only as Christina by SVT's investigative news programme Uppdrag Granskning last week, woke up after the surgery, newspaper Sydsvenskan reported on Friday.
Four nurses blew the whistle on the changes to the case file three days after the surgery in Gdansk. A hospital director hid the note and suspicious case, the report said.
According to the false medical records, the Swedish woman woke up after the surgery in August, had contact with the staff and was able to orient herself.
In reality, however, the surgery resulted in the woman receiving a serious brain injury, leaving her in a coma from which she has not woken.
More information was also likely forged, Polish newspaper Gazeta Wyborcza added.
The hospital director has not been able to explain her actions and has been dismissed. The incident has attracted intense scrutiny in the Polish news media and an investigation by prosecutors in Gdansk into the procedure is under way.
Swedish medical tourism company Medica Travel arranged the breast surgery at a clinic belonging to a state hospital in the Polish port city. However, the hospital does not have authorisation to operate on private foreign patients.
The 31-year-old woman received the surgery as a gift from her fiancé ahead of her wedding next year. She has since returned to Sweden and is now cared for at Skåne University Hospital. The possibility of her regaining consciousness is considered remote.
According to Polish authorities, the hospital in Gdansk could be liable for the unsuccessful operation.