Recent diagnostic experience with subdural empyema.

The authors review the Neurological Institute experience of six cases of subdural empyema in the 4 years since the introduction there of computerized tomography (CT) scanning. Four patients had no known prior neurological disease, and presented with the classical clinical syndrome of fever, depressed sensorium, and focal seizures; three of these patients had histories or radiographic evidence of sinus disease. The two remaining patients had undergone earlier drainage procedures for chronic subdural hematomas, and presented without neurological symptoms but with low-grade fever and signs of local wound infection. All of the patients of the former (primary) empyema group had technically satisfactory contrasted CT scans at a time when the clinical syndrome was fully developed, and none revealed the subdural collection. Angiograms were performed in three of these cases and were uniformly successful in demonstrating the collections and suggesting their inflammatory natures. Both secondary empyemas were readily visualized by CT, and showed characteristic brightly enhancing membranes. It is concluded that primary and secondary subdural empyemas differ both in clinical presentation and in accuracy of CT diagnosis. In the former group, evidence of sinus disease is suggestive but does not by its absence exclude a purulent subdural collection. In patients with the typical clinical syndrome, reliance on CT is hazardous, and angiography is the diagnostic procedure of choice.