Fusobacterial brain abscess: a review of five cases and an analysis of possible pathogenesis

Object. The cases of five patients with fusobacterial brain abscess are presented. The authors discuss their attempt to determine the pathogenesis. Methods. The clinical and microbiological features of five cases of fusobacterial brain abscess are reviewed. Isolates of 2031 Fusobacterium spp. and other anaerobes collected (1989-2002) at our institution were analyzed and compared for incidences and isolation sources. The findings were correlated with extensive literature on the subject. The five patients were men between 45 and 74 years of age. All experienced an insidious onset of the disease and probable hematogenous seeding of the organism(s). One patient had a monomicrobic Fusobacterium necrophorum abscess, whereas the others had polymicrobic F. nucleatum abscesses. Despite surgery and a regimen of antibiotic medications and dexamethasone, three patients experienced a paradoxical deterioration 3 days postoperatively that necessitated reevacuation of the lesion. The evacuants observed at that time contained numerous leukocytes but no microorganisms, suggesting intensified inflammation as the likely cause of deterioration. This explanation is supported by literature that fusobacteria strongly activate neutrophils. An analysis of the 2031 anaerobes from blood, wounds, and abscesses showed the considerable virulence of Fusobacterium spp., which were able to enter and/or sustain themselves in the blood circulation. This pattern was similar to that of Clostridium spp., but different from those of Peptostreptococcus spp., Bacteroides spp., and Prevotella spp., which were less invasive but more abundant. Conclusions. Some fusobacterial brain abscesses may be associated with a paradoxical postoperative deterioration, which is probably due to intensified inflammation following treatment. The blood-borne dissemination and invasive behavior of fusobacteria likely initiate such a brain abscess, and further seeding of other synergic bacteria leads to a polymicrobic abscess.