Meningorectal fistula as a cause of polymicrobial anaerobic meningitis.

A 49-year-old diabetic woman developed polymicrobial anaerobic meningitis secondary to a meningorectal fistula one year after receiving neutron beam therapy for a rectal adenocarcinoma. The meningitis was refractory to chloramphenicol and penicillin but responded to oral metronidazole. Sustained eradication of meningitis was achieved with continued metronidazole for 51/2 months, despite persistence of the fistula. Metronidazole may be a superior antimicrobial agent for polymicrobial anaerobic meningitis, especially when caused by a large or continuing bacterial inoculum. This meningorectal fistula is the first of its kind to our knowledge to be demonstrated by microbiologic, radiologic, and pathologic studies.