Fusobacterium brain abscess as a complication of sinusitis in an immunocompetent adolescent: A case report

Brain abscesses are uncommon intracranial infections with an estimated incidence of 0.5 per 100000 individuals. Among bacterial causes, Fusobacterium species account for less than 10% of cases, and fewer than 20 pediatric instances have been reported worldwide. These infections are predominantly seen in individuals with poor dental hygiene, sinusitis and pose diagnostic challenges due to their anaerobic nature and frequent culture negativity. However, cases in immunocompetent individuals are rare and often pose diagnostic challenges due to the anaerobic nature of the causative organisms.

We report a 15-year-old boy who presented with a 5-day history of fever, headache, vomiting, and altered sensorium, followed by status epilepticus. Clinical, imaging, and laboratory data were systematically collected. Magnetic resonance imaging revealed bilateral frontal and left temporal subdural abscesses with frontal sinusitis. Pus obtained during burr-hole drainage underwent conventional culture and broad-range 16S rRNA next-generation sequencing (NGS) to identify the pathogen. Initial aerobic and anaerobic cultures were sterile. NGS identified Fusobacterium nucleatum as the etiological agent. Empirical antibiotics (ceftriaxone, vancomycin, and metronidazole) were streamlined to ceftriaxone plus metronidazole after confirmation. The patient required repeat burr-hole drainage due to paradoxical effusion enlargement caused by inflammatory response following bacterial lysis. After four weeks of targeted therapy, he achieved full neurological recovery, with normalization of inflammatory markers and complete resolution on follow-up imaging.

This case underscores the diagnostic value of 16S rRNA sequencing in culture-negative brain abscesses and highlights the importance of multidisciplinary management combining surgical source control and targeted anaerobic therapy. Early recognition and appropriate treatment of sinusitis, in line with IDSA recommendations, may prevent severe complications such as Fusobacterium brain abscess.