Post-traumatic subdural hygromas: observations concerning a surgical enigma.

Four per cent (38) of 881 head injured patients developed known subdural hygromas. Their times of onset and course were variable. However, only two large hygromas seemed clinically significant. Hygromas were more frequent when intracranial pressure monitors were placed, possibly due to opening of the arachnoid, particularly if intracranial pressure was low. But, of course, monitors were only inserted in more severely injured patients. The use of Richmond bolts to drain subdural hygromas in a controlled fashion while monitoring intracranial pressure is suggested.