Trepanning
Trepanning was one of the more gruesome medieval medical practices, but strangely enough it was one of the practices with a high survival rate. Trepanning was used to treat a range of issues including seizures, skull fractures, headaches, and mental illnesses.
Trepanning involved cutting a hole in the skull and exposing the dura matter. Once the dura matter was exposed it was believed that whatever bad things were causing the illness or strange behavior would be released from the brain. There was little else to the procedure other than cutting a relatively large hold in the head. Trepanning was only performed on adults and with equal frequency of men and women, however the frequency did increase with wealth and age. This suggests the procedure may have either been expensive or the wealthy were more likely to seek a cure for the strange behaviors of their relatives.
By the 16h century there were even specific devices created to make the trepanning process easier on the physician. The process was rarely easy on the patient. Even through there was knowledge of anesthesia, and there were mixtures used to put patients into deep sleep, they were very risky. Sometimes the mixture involved too much hemlock and the patient never woke up. In some cases, physicians opted to skip the risk involved with anesthesia.
There have been 8 skulls found from the period from the 6th to the 8th centuries that showed evidence of trepanning. Of the 8 skulls, 7 showed signs of healing and survival which suggests that there were low infection rates with trepanning and high survival rates when compared with other procedures like bloodletting.