[Encapsulated subdural empyema--a case report with special reference to CT findings and operative indications].

A case of encapsulated subdural empyema was reported. This 1.5-year-old boy was admitted with the increasing confusion and convulsion. Eight months prior to admission, he had craniotomy for traumatic acute epidural hematoma on the left side. Following a coagulation of the middle meningeal artery which was the bleeding source, the dura was opened but no cortical damage was noted at that time. The computed tomographic (CT) scan on admission revealed a large subdural collection with a thin enhancing rim on the left side. Emergency craniotomy revealed a collection of subdural pus, which was irrigated and a catheter was put for continuous drainage. Postoperatively, the patient did well, however, following removal of the catheter, three weeks after the first operation, the subdural empyema was reexpanded with a very thick enhancing rim on CT scan. Ultrasonography also clearly demonstrated the formation of the thick membranes. The large craniotomy was performed and empyema with the outer and inner membranes of 8 mm thick was totally excised. Postoperative CT scan did not show any enhancing rim, indicating that enhancement was caused by newly formed vessels within the membranes per se. This findings are totally different from those observed in the brain abscess in which ring enhancement on CT continues months to years following so-called extracapsular excision of abscess. In the brain abscess, surrounding glial tissue with plenty neovascularization is left intact, even after the operation.