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

Abstract

BACKGROUND

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.

CASE SUMMARY

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.

CONCLUSION

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.

Key Words: Brain abscess; Fusobacterium nucleatum; Subdural empyema; Sinusitis; Next-generation sequencing; Status epilepticus; Case report

Core Tip: Fusobacterium nucleatum brain abscess is an uncommon but serious complication of sinusitis, especially in immunocompetent children. Conventional cultures often remain sterile because of the organism’s anaerobic nature. This case illustrates the value of 16S rRNA next-generation sequencing for rapid pathogen identification and targeted therapy. Early neurosurgical drainage with appropriate anaerobic coverage resulted in full neurological recovery.

INTRODUCTION

Brain abscess is a rare but serious intracranial infection with a reported incidence of 0.2-1.9 per 100000 person-years[1,2]. Although uncommon, it remains an important cause of neurological morbidity in children, particularly in low- and middle-income countries[3]. Sinusitis, otitis media, cyanotic congenital heart disease, and cranial trauma are recognized predisposing factors[4]. Fusobacterium accounts for less than 10% of all bacterial brain abscesses, and pediatric cases constitute under 20 reported instances worldwide, emphasizing its rarity and diagnostic challenge[5]

Fusobacterium species are obligate anaerobic Gram-negative bacilli forming part of the normal oropharyngeal flora and are most frequently implicated in head-and-neck infections such as Lemierre’s syndrome. Among these, Fusobacterium nucleatum is an uncommon cause of isolated Central Nervous System infection, especially in immunocompetent individuals. Conventional aerobic cultures often fail to isolate these organisms due to their strict anaerobic requirements and prior antibiotic exposure.

Recent advances in culture-independent diagnostics, including broad-range 16S rRNA amplification and metagenomic next-generation sequencing (NGS), have enhanced detection of fastidious pathogens in culture-negative brain abscesses[6,7]. Current Infectious Diseases Society of America and American Heart Association guidelines emphasize early neuroimaging, prompt surgical drainage, and targeted antimicrobial therapy guided by microbiological or molecular confirmation[8-10].

We report a case of Fusobacterium nucleatum brain abscess secondary to sinusitis in an immunocompetent adolescent, highlighting the diagnostic role of NGS and successful outcome with targeted therapy.

Clinical information was collected prospectively during hospitalization at Kanchi Kamakoti Childs Trust Hospital, Chennai. The patient was managed by a multidisciplinary team (pediatric neurology, infectious disease, and neurosurgery). Presentation details, clinical course, and examination findings were documented in electronic medical records.

Laboratory parameters were retrieved from the hospital system. Pus and cerebrospinal fluid samples were processed for aerobic and anaerobic cultures. When cultures remained sterile, stored pus aliquots (-80 °C) underwent broad-range 16S rRNA sequencing (Bactifast NGS platform). Magnetic resonance imaging (MRI) and computed tomography (CT) were used to monitor disease evolution. Treatment records included antibiotic regimens, surgical interventions, and outcomes. Follow-up data on neurological recovery were obtained at outpatient review. Patient identifiers were anonymized and parental consent obtained.

CASE PRESENTATION

Chief complaints

A 15-year-old previously healthy adolescent male presented with history of 6-days of fever and headache, followed by 2 days of altered sensorium.

History of present illness

He was found to have low grade, intermittent fever for 5 days associated with throbbing type of headache, in the frontal region. There was history of altered sleep wake pattern for 2 days and unusual behavioural change noticed by the parents.

History of past illness

There was no past history of seizure disorder or any illness requiring hospital admissions.

Personal and family history

Family history was unremarkable for neurological illness.

Physical examination

Lethargic, confused, and encephalopathic, Glasgow Coma scale: 11/15, bilateral pupils 3 mm reacting to light. Deep tendon reflexes exaggerated, with bilateral plantar extensor. No cranial nerve palsies. Other system examination: Normal.

Heart rate: 112/minute, blood pressure: 100/69 mmHg, SpO₂ 98% in room air, temp-100 Fahrenheit.

Laboratory examinations

Table 1 summarizes laboratory findings from the referring hospital and our institute. The child showed elevated inflammatory markers [C-reactive protein (CRP) 113 mg/L; ESR 50 mm/hour] and neutrophilic leukocytosis. Conventional cultures were sterile, while NGS from pus identified Fusobacterium nucleatum, confirming the etiology.

Table 1 Investigations done in the referring hospital and in our institute.

Parameter	Referring hospital	Our institute
Total count (cells/µL)	17000	13400
Neutrophils (%)	56	87
CRP (mg/L)/ESR (mm/hour)	92/-	113/50
Urea (mg/dL)/creatinine (mg/dL)	26/0.5	35/0.87
CSF protein (mg/dL)	88	-
CSF sugar (mg/dL)	40	-
CSF cells (/µL)	496	114
CSF GeneXpert	Negative	Negative
CSF culture	No growth	No growth
Pus culture	Not done	No growth
Blood culture	No growth	No growth
16S rRNA (NGS) from pus	Not done	Fusobacterium nucleatum

CRP: C-reactive protein; ESR: Erythrocyte sedimentation rate; CSF: Cerebrospinal fluid; NGS: Next-generation sequencing.

Imaging examinations

MRI of the brain demonstrated bilateral frontal and left temporal subdural enhancing collections extending into the anterior interhemispheric fissure, with diffuse pachymeningeal enhancement suggestive of meningitis (Figure 1A-C). Associated sinusitis involving the frontal, ethmoidal, and maxillary sinuses with left periorbital soft tissue swelling was noted, indicating contiguous spread from the paranasal sinuses (Figure 1D). Postoperative CT of the brain revealed residual left frontotemporal effusion and postoperative changes following burr-hole craniotomy (Figure 1E). A repeat CT performed on day 10 showed paradoxical enlargement of a right-sided subdural effusion, attributed to inflammatory response and bacterial lysis after initiation of targeted antibiotic therapy (Figure 1F). Sequential imaging findings depicting disease progression, surgical intervention, and recovery are shown in Figure 1.

Figure 1 Neuroimaging and intraoperative findings in a 15-year-old male with Fusobacterium nucleatum brain abscess secondary to sinusitis. Magnetic resonance imaging (MRI) brain demonstrating bilateral frontal subdural empyema and left frontal sinusitis. A: Axial T2-weighted image showing left frontal subdural collection with mass effect (arrow); B: Axial fluid-attenuated inversion recovery sequence revealing hyperintense collection and midline shift (arrow); C: Axial T1 post-contrast image showing ring enhancement of the abscess cavity (arrow); D: Coronal MRI depicting frontal sinusitis with contiguous spread to the left frontal lobe (arrow); E and F: Computed tomography (CT) brain showing postoperative findings. CT performed on day 4 revealing residual left frontotemporal effusion (arrow) (E). Repeat CT on day 10 demonstrating paradoxical enlargement of right-sided subdural effusion (arrow) following effective antibiotic therapy (F); G and H: Intraoperative images during burr-hole craniotomy showing exposure of the left frontal bone and aspiration of thick purulent material (approximately 100 mL). MRI: Magnetic resonance imaging; CT: Computed tomography.

MULTIDISCIPLINARY EXPERT CONSULTATION

Neurosurgery: Child underwent craniotomy, evacuation of empyema, and excision of the left frontal sinus. A repeat burr hole was also required eventually due to increase in size of the subdural effusion with poor response in clinical status.

Infectious disease: Child was empirically started on Ceftriaxone, vancomycin and Metronidazole. After isolation of Fusobacterium from pus through 16 s ribonucleicacid, vancomycin was stopped and ceftriaxone and metronidazole were continued.

FINAL DIAGNOSIS

Right frontoparietal and left fronto temporal subdural abscess with empyema.

TREATMENT

He was initially admitted to an outside facility where he developed seizures and was treated with anti-epileptics. With recent onset of fever, headache and altered sensorium, provisional diagnosis of meningoencephalitis was made and was treated empirically with ceftriaxone, vancomycin and acyclovir. Subsequently child developed multiple episodes of seizures and was referred to tertiary care centre for further management.

At our institute, he was intubated on Day 2 due to worsening sensorium and recurrent seizures, requiring mechanical ventilation for 48 hours. He was extubated on Day 4 and transitioned to room air with stable oxygen saturation.

Following surgery- burr hole craniotomy and evacuation of pus (Figure 1G and H), the child’s sensorium gradually improved, and no further seizures were noted. Pus samples from the surgical site showed neutrophilic predominance; culture results were pending. Blood cultures were negative. Child was continued on ceftriaxone, vancomycin, and metronidazole. He was hemodynamically stable and tolerated nasogastric feeds. Aphasia, increased muscle tone, and brisk reflexes were noted on neurological examination. Despite antibiotic therapy, persistent fever spikes continued. Bactifast NGS of the pus revealed Fusobacterium species. Vancomycin was discontinued, and ceftriaxone with metronidazole was continued.

Repeat CT brain (Figure 1E and F) revealed an increase in right subdural effusion, indicating progression. Neurosurgical re-evaluation led to a decision for repeat burr hole drainage.

The child underwent repeat burr hole drainage of the right subdural abscess. He remained seizure-free and showed no signs of raised intra cranial pressure (ICP).

OUTCOME AND FOLLOW-UP

Over the next several days in the ward, he transitioned from nasogastric to oral feeds and began to regain speech and motor functions. Aphasia resolved significantly, and the child became verbal and ambulatory with the aid of daily physiotherapy. Laboratory markers of infection showed significant improvement with CRP decreasing from 136 mg/L to 13 mg/L. After completing a 4-week course of intravenous ceftriaxone and metronidazole, the child was discharged in stable condition, on oral diet, afebrile, seizure-free, and with no neurological deficits. The chronological sequence of clinical events, investigations, neurosurgical interventions, and recovery is summarized in Figure 2 (timeline).

Figure 2 Clinical timeline of presentation, management, and recovery in a child with Fusobacterium nucleatum brain abscess secondary to sinusitis. Day -5 to 0: Fever, headache, and altered sensorium led to magnetic resonance imaging showing bilateral frontal and left temporal subdural abscess with sinusitis. Day 0-2: Empirical ceftriaxone, vancomycin, and metronidazole were initiated; burr-hole drainage performed. Day 4-7: Gradual neurological improvement, persistent fever. Day 8-10: Next-generation sequencing confirmed Fusobacterium nucleatum; vancomycin stopped, ceftriaxone and metronidazole continued. Day 12-14: Repeat computed tomography showed paradoxical effusion enlargement; repeat drainage performed. Day 15-28: C-reactive protein decreased (136 mg/L→13 mg/L); afebrile, seizure-free. Follow-up: Completed 4-week IV antibiotics; discharged neurologically intact with normal speech and gait. MRI: Magnetic resonance imaging; CT: Computed tomography; IV: Intravenous; NGS: Next-generation sequencing; CRP: C-reactive protein; BI: Bilateral.

DISCUSSION

This case illustrates a classical yet complex presentation of pediatric subdural empyema, complicated by seizures, status epilepticus, and multiple intracranial collections. Early neuroimaging with MRI was crucial in identifying the empyema and associated sinusitis. The case reinforces the need to consider intracranial abscess in any child with prolonged fever, altered sensorium, and focal neurological deficits, especially in the setting of sinusitis.

The isolation of Fusobacterium—an anaerobic organism commonly associated with Lemierre’s syndrome and head and neck infections—provided clarity on the aetiology] Empiric broad-spectrum antibiotics including ceftriaxone, vancomycin, and metronidazole were appropriate pending microbiological confirmation. The targeted discontinuation of vancomycin following Fusobacterium detection reflects prudent antimicrobial stewardship.

On reviewing the literature (Table 2)[11-13], inappropriate or delayed antibiotic therapy may fail to adequately control infection, allowing the immune system to induce localized fibrosis and cortical ischemia in an attempt to contain bacterial spread[14]. In contrast, after initiation of effective antimicrobial therapy, a paradoxical radiological enlargement of the subdural effusion may occur due to bacterial lysis and the ensuing inflammatory response[15]. This transient increase in collection size reflects treatment activity rather than failure and should be interpreted cautiously to prevent unnecessary repeat surgical intervention or escalation of antibiotic therapy.

Table 2 Pediatric cases of Fusobacterium brain abscess in different clinical settings.

Ref.	Age/sex	Risk factors	Findings (organism and imaging)	Treatment and outcome
Multiple brain abscesses and bacteremia (Meis et al[11], 1993)	6 years/female	Recent Mycoplasma pneumoniae infection	Fusobacterium necrophorum; multiple brain abscesses	Penicillin G + metronidazole × 2 months → complete recovery
Brain abscess after intraoral laceration (Ochi et al[12], 2020)	9 years/female	Cyanotic CHD; intraoral trauma	Fusobacterium nucleatum + others; single abscess (15 mm × 10 mm) in left internal capsule with edema	Craniotomy drainage + ceftriaxone × 8 weeks → good recovery
Unusual neurological presentation (Haddad et al[13], 2016)	2 years/female	Tonsillitis; delayed treatment	Fusobacterium necrophorum; multiple cerebral abscesses + subdural empyema	Meropenem × 6 weeks + surgery → favorable outcome
Current case (present report)	15 years/male	Acute bacterial sinusitis; immunocompetent	Fusobacterium nucleatum; bilateral frontal subdural abscess with empyema	Burr-hole drainage + ceftriaxone + metronidazole × 4 weeks → full recovery

CHD: Congenital heart disease.

Surgical drainage remains the cornerstone of treatment in subdural empyema, especially when clinical deterioration, increased ICP, or mass effect is evident[16,17]In this patient, initial craniotomy followed by burr hole drainage was necessary due to bilateral empyema and worsening sensorium.

Despite initial neurological compromise, the child made a near-complete neurological recovery with neurorehabilitation. The early initiation of physiotherapy and nutritional support were essential to optimizing outcomes.

CONCLUSION

This case underscores the importance of considering brain abscess in children presenting with fever, headache, seizures, or altered sensorium, particularly in the context of sinusitis. Culture-negative intracranial collections necessitate advanced molecular diagnostics such as 16S rRNA sequencing, which can identify fastidious pathogens and guide antibiotic stewardship. Early neurosurgical source control and multidisciplinary supportive care remain pivotal to favourable outcome.

This case highlights the diagnostic and therapeutic challenges of pediatric subdural empyema secondary to sinusitis. Despite sterile cultures, broad range 16S rRNA gene sequencing enabled identification of Fusobacterium nucleatum as the causative pathogen, allowing for targeted antimicrobial therapy and appropriate stewardship. The clinical course further emphasizes that paradoxical radiological enlargement of empyema may occur following initiation of effective antibiotics and should not be mistaken for treatment failure.

Timely neurosurgical intervention, guided antimicrobial therapy, and structured rehabilitation together contributed to a near complete neurological recovery in this child. Our experience reinforces the role of molecular diagnostics in culture-negative intracranial infections and underscores the need for a multidisciplinary approach to optimize outcomes in pediatric brain abscesses.

ACKNOWLEDGEMENTS

We would like to extend our sincere thanks to Dr Santhosh Mohan Rao, Paediatric Neurosurgeon for his timely intervention and management of the case.