Role of anaerobic bacteria in subdural empyema. Report of four cases and review of 327 cases from the English literature.

Anaerobic bacteria were isolated from the subdural space in all four cases of subdural empyema encountered over a 2 and a half year period. Only one aerobe was isolated in these cases. The bacteriology of subdural empyema was further analyzed from a review of 327 cases reported in the English literature. Anaerobes accounted for 12 per cent of 234 cases; In addition, 27 per cent of cases were reportedly "sterile." These data support our finding that anaerobic bacteria may play a far more important role in subdural empyema than was previously appreciated.