"Subacute" postoperative subdural empyema.

Although subdural empyema (SDE) has long been a recognized postoperative complication, little has been written to suggest that SDE's following operative procedures are different from those occurring in patients who have not had previous surgery. Four cases of postoperative SDE are reported which seem to have several distinguishing features and are grouped under the title of "subacute" subdural empyemas. These include: occurrence in a previous craniotomy site, a prolonged course, the insidious onset of symptoms, and the absence of signs of constitutional illness. The presence of an inner subdural membrane which limits the size of the empyema and separates it from the underlying brain is thought to be the reason for the relatively benign nature of the presenting symptoms and the extremely good prognosis. Computerized tomography scanning was not able to provide a preoperative diagnosis of empyema in any case.