Fusobacterium nucleatum as an Emerging Culprit in Brain Abscesses: A Narrative Synthesis of 25 Years of Clinical and Diagnostic Data

Brain abscesses are life-threatening infections, predominantly caused by anaerobic organisms. The role of oropharyngeal microbiota, presence in dental plaque biofilms, and hematogenous spread is established in the literature. However, due to its rare occurrence, limited literature is available on its management. The rationale of this narrative review was to elucidate risk factors, treatment strategies, and outcomes of brain abscesses caused by Fusobacterium nucleatum (F. nucleatum). After a detailed literature search using PubMed, 12 cases were analyzed, containing a total of 13 patients, over the period of the last 24 years, between 2000 and 2024. All case reports and case series, including data relevant to brain abscess caused by F. nucleatum, were included, while letters to the editor and non-human studies were excluded. The main findings were male predominance (nine (69.23%)). The clinical presentations were headache (seven (53.85%)), fever (five (38.46%)), and neurological deficit (four (30.77%)), predominantly found in patients with poor oral health (seven (53.85%)), extracranial abscess sources with the presence of F. nucleatum (four (30.76%)), and alcohol consumption (four (30.76%)). Magnetic resonance imaging was the most commonly used radiological investigation in the majority of patients (nine (69.23%)). In biochemical investigations, blood cultures (eight (61.53%)) yielded negative results. However, brain abscess culture (four (30.76%)) as well as nucleic acid amplification test/polymerase chain reaction on culture-negative samples showed the presence of F. nucleatum. The majority of the treatment strategies were both surgical and medical. The surgical intervention involved craniotomy (three (23.07%)) and extraventricular drain placement, while medical management included courses of antibiotics such as metronidazole (eight (61.53%)), ceftriaxone (three (23.07%)), penicillin (three (23.07%)), and steroids (three (23.07%)). Injectable metronidazole 500 mg thrice daily was given for an average of 13 weeks, and injectable ceftriaxone 2 g once daily was given for an average of six weeks. Our results indicated that a combination of surgical and medical treatment leads to improvement in 10 (76.92%) patients. Follow-up MRI in four patients at an average of 23.4 weeks showed complete resolution in two (15.38%) patients and a reduction in abscess cavity size in the other two (15.38%). This review underscores that both medical and surgical treatment together resulted in better outcomes for F. nucleatum brain abscesses and also advocates for oral examination in patients with brain abscesses, with prioritization of the identification of the primary source of infection.