J Korean Ster Func Neurosurg > Volume 18(1); 2022 > Article
Ahn and Lee: Factors influencing the outcomes and mortality of brain abscess: a retrospective analysis of 54 cases

Abstract

Objective

Brain abscess is relatively uncommon because the brain has an abundant blood supply and protection from the blood-brain barrier. The objective of this study was to analyze the outcomes of brain abscesses and to identify factors associated with patients’ outcomes.

Methods

The characteristics (age, sex, medical history, initial neurologic status, laboratory data, abscess morphology) and outcomes of 54 patients with brain abscesses who underwent surgical treatment at our hospital from January 2011 to December 2020 were retrospectively analyzed.

Results

There were more male patients than female patients (44:10). Sixteen patients died or became disabled, whereas 38 patients recovered. Statistical analyses indicated that those with a penetration cause, Glasgow coma scale≤12, ventriculitis, or Gram-negative bacilli grown in abscess culture had significantly poorer outcomes, whereas those with a contiguous cause and isolated brain abscess had significantly better outcomes (p<0.05).

Conclusion

This study identified poor prognostic factors in brain abscess patients. Despite advances in diagnosis and treatment techniques, brain abscess still has a high mortality rate. The results of this study are expected to help with exact diagnoses and more accurate prognostication of brain abscess patients.

INTRODUCTION

Brain abscess is relatively uncommon because the brain has an abundant blood supply and protection from the blood-brain barrier. Reported incidence of brain abscess ranges from 0.4 to 0.9 cases per 100,000 population [1]. Before antibiotics were discovered, brain abscesses were almost uniformly lethal [1]. With the introduction of computed tomography (CT) scanning and stereotactic techniques, the outcome of brain abscess has dramatically improved [2]. Brain abscess remains a rare disease. Only a few studies have assessed its etiology and pathogens [1,2]. The incidence of brain abscess may vary depending on the region, time, and environment. Therefore, it is necessary to check whether symptoms, medical history, and causative bacteria of brain abscess patients proposed in previous studies are applicable at the current time and place. The purpose of this study was to analyze the outcomes and influencing factors of brain abscess after surgical treatment.

MATERIALS AND METHODS

Patients

Medical records of patients with brain abscess at our hospital from January 1, 2011 to December 31, 2020 were retrospectively reviewed. Brain abscess was defined as a localized brain parenchymal lesion with ring enhancement by contrast medium and perilesional edema visible on cranial CT scan or magnetic resonance imaging (MRI). It was associated with at least one of the following three characteristics: positive blood culture, positive culture of intracerebral materials, and histology of intracerebral lesions suggesting brain abscess. Those with the presence of extracranial abscess such as subdural and epidural empyema were excluded. A total of 74 patients had medically recorded brain abscess. However, 20 patients did not satisfy the above criteria for brain abscess. Thus, 54 patients who satisfied the criteria of this study were analyzed.

Pre- and postoperative evaluations

Clinical data included age at diagnosis, sex, medical history, symptoms, initial neurological status, predisposing factors, surgical procedures, abscess characteristics (location, numbers, size), and treatment modalities. Level of consciousness was evaluated by the Glasgow coma scale (GCS). Patients were divided into GCS>12 and GCS≤12 groups for analysis based on possibility of cooperation. Cure with minimal or no residual damage was defined as moderate disability (having a disability but being independent) and good recovery. Residual neurologic disability was defined as persistent vegetative status and severe disability. This study was approved by the Institutional Review Board of Pusan National University Hospital (approval number: H-2204-013-114).

Statistical analysis

All statistical analyses were performed with IBM SPSS ver. 28.0 (IBM Corp., Armonk, NY, USA). Results are expressed as percentage and mean±standard deviation. Student’s t-test, Fisher’s exact probability test, and chi-squared test were used for the statistical analysis. Logistic regression analysis was performed to identify significant factors affecting outcomes of brain abscess patients. The statistical threshold was set at p<0.05 (two-tailed) to determine significance.

RESULTS

Clinical presentation

There were 44 male and 10 female patients. Their average age at diagnosis was 55.0±18.0 years (range, 1-85 years). On admission, most patients had focal neurologic deficit such as facial palsy, hemiplegia, aphasia and visual disturbance (35.2%), altered mentality (27.8%), and signs of increased intracranial pressure such as headache, nausea, vomiting, and papilledema (31.5%). Seizures occurred in 9 patients (16.7%) and fever occurred in 7 patients (13.0%). A total of 39 patients (72.2%) presented with known predisposing factors, including otitis media, sinusitis, dental infection, penetrating trauma or secondary to neurosurgical procedure, lung infection, and heart infection. Thirty-five patients (64.8%) presented with contiguous infections (otitis media, sinusitis, dental infection). Eight patients (14.8%) had poor-controlled diabetes mellitus. There was no immunosuppressive patient. Four patients had brain abscesses related to hematogenous spread, including two with lung infection and two with heart infection (Table 1).

Image characteristics

All patients had MRI scans (Fig. 1, 2), which showed single abscess in 49 (90.7%) and multiple ones in 5 (9.3%). The most common location for abscesses was the frontal lobe (38.9%), followed by the parietal lobe (24.1%), temporal lobe (22.2%), and occipital lobe (22.2%) (Table 2). There was no abscess in brain stem. Mean abscess size was 3.1 cm, showing no significant difference between the cure group and the death or disability group.

Pathogen findings

Microbiological studies consisted of cultures of brain abscess materials for all patients. Cultures of abscess materials remained no growth for 12 patients (22.2%). Among 42 patients with positive cultures from brain abscess materials, 34 had single pathogens and nine had multiple pathogens. The most common pathogens were Gram-positive cocci (streptococci, staphylococci) (53.7%), followed by anaerobes (22.2%) and Gram-negative bacilli (18.5%). Blood culture was performed for all patients. Only four patients had a positive blood culture (positive growth of bacteria). Of them, three showed the same pathogen in both blood and brain abscess, suggesting that hematogenic dissemination of the brain abscess.

Treatment

All 54 patients underwent surgical treatment. One had craniectomy. Twenty-eight had drainage by craniotomy and 25 had stereotactic aspirations. All patients were treated with antibiotics for at least 6 weeks. Operation modalities were chosen depending on the surgeon’s preference and the location of the abscess.

Outcome

A total of 38 patients (70.4%) had a cure with minimal or no residual damage. A total of 16 patients (29.6%) had a death or residual neurologic disability. Three died during hospitalization. Thirteen had moderate or severe disability. Deaths were caused by underlying systemic infection. This study revealed that patients who had isolated brain abscesses had better outcomes (p=0.002) (Table 1). Those with contiguous infections (otitis media, sinusitis, dental infection) had better outcomes (p=0.024) (Table 1). Those with penetrating trauma or secondary to neurosurgical procedure had significant poor outcomes (p=0.003) (Table 1). Those with GCS score of 12 or less had poor outcome (p=0.043) (Table 1). Those with Gram-negative bacilli identified had poor outcomes (p=0.004) (Table 2).

DISCUSSION

Brain abscess can be caused by bacteria, mycobacteria, fungi, or parasites (protozoa and helminths). Its reported incidence ranges from 0.4 to 0.9 cases per 100,000 population [3,4]. Causes of brain abscesses include underlying diseases such as human immunodeficiency virus, taking immunosuppressants, destroying brain barriers (surgery, trauma, otitis media, periodontitis, sinusitis), systemic endocarditis, and bacteremia. Previous studies have reported that infections caused by contiguous penetration of causative bacteria account for about half and other infections caused by hematogenic dissemination account for about a third, while the rest have unknown causes of infection [5].
In this study, 64.8% of patients had a contiguous cause and 7.4% had a hematogenic cause, whereas causes for the rest were identified as unknown. Treatment prognosis for patients with a contiguous cause was good (p=0.024) (Table 1).
The causative bacteria of brain abscess can vary [6], including Gram-positive, Gram-negative, and anaerobes, with Gram-positive cocci being the most at 53.7% in this study. In addition, 22.2% of cases had no bacteria detected. Gram-negative bacilli accounted for 18.5%. For such cases, treatment prognosis was significant poor. It can be estimated that concentration of antibiotic acting against Gram-negative bacteria is not enough in cerebrospinal fluid, and multi-drug resistance of Gram-negative bacteria. Thus, new antibiotics usage or changing dosage and new infusion methods such as intra-ventricular injection should be considered to improve treatment prognosis.
Critical clinical manifestation of brain abscess includes headache, fever, and alternated level of consciousness. In addition, 25% of patients might have symptoms of convulsions [5]. Patients might also have local neurological symptoms depending on the location, size, and degree of swelling of the abscess [7], which requires differential diagnosis from brain tumors, cerebral infarction, bleeding, and so on. In this study, there were 13.0% of patients with fever, 31.5% of patients with cerebral hypertension symptoms including headaches, and 27.8% of patients with decreased consciousness. The most common symptom was local neurologic defect, which was found to account for about 35.2%. Headache, fever, and loss of consciousness are still thought as traditional symptoms of brain abscess. However, this is a low-specific symptom that requires differentiation from other diseases, so advanced imaging tests, laboratory findings, and comprehensive judgment of clinical symptoms are needed to diagnose brain abscess. Lumbar puncture should be performed only when there is clinical suspicion of meningitis or abscess rupture into the ventricular system and when there are no contraindications for lumbar puncture, such as brain shift on cranial imaging or coagulation disorders [8].
Brain abscess surgery is a very important treatment process for identifying the causative bacteria and reducing the size of abscess. Brain abscess removal has traditionally been performed using stereotactic neurosurgical techniques. Recently, it has been performed using a stereotactic navigation system [9]. Continuous maintenance of the catheter is not generally recommended [10]. Some researchers advise direct antibiotic injection into the abscess cavity through the catheter because intravascular transmittance of antibiotics in the blood is not high. However, such treatment is not generally recommended due to insufficient research on its risks and benefits. Since the prognosis of Gram-negative patients was very poor in this study, the benefit of direct injection of antibacterial agents into the catheter only for patients with Gram-negative bacilli identified might need to be studied in the future. After bacterial identification, antibiotic treatment is required for a total of 6 to 8 weeks with antibacterial agents that identified bacteria are sensitive to [11].

CONCLUSION

This study is not suitable for all patients to discuss the treatment method using the standard antibiotic treatment method. Results of this study are expected to help with exact diagnosis and prognosis prediction of brain abscess patients. Further studies are needed to improve the poor prognosis of patients with brain abscess due to Gram-negative bacilli. The outcome of brain abscess depends on exact diagnosis and comprehensive treatment plans including surgery and antibiotics.

NOTES

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

Fig. 1.
Magnetic resonance images of patients diagnosed with brain abscess. Images of a patient with Escherichia coli and Enterobacter cloacae identification. (A) T1-weighted, contrast-enhanced axial image demonstrating ring enhancement and central low intensity. (B) Diffusion-weighted axial image revealing abnormal hyperintensity within the nonenhancing central cavity, indicating a marked restriction of water diffusion in this lesion.
jksfn-2022-00164f1.jpg
Fig. 2.
Magnetic resonance images of patients diagnosed with brain abscess. Images of a patient with Streptococcus identification and blood culture positivity. (A) T1-weighted, contrast-enhanced axial image showing a ring enhancement with surrounding hypointense edema. (B) Diffusion-weighted axial image demonstrating abnormal hyperintensity, indicating marked restriction of water diffusion.
jksfn-2022-00164f2.jpg
Table 1.
Clinical presentation of patients with brain abscess, with a statistical analysis of factors associated with their outcomes
Parameter Presentation Total (n=54) Death or disability (n=16) Cure (n=38) p-value
Sex Male 44 (81.5) 14 (25.9) 30 (55.6) 0.705
Female 10 (18.5) 2 (3.7) 8 (14.8)
Age (yr) 55.0±18.0 59.4±20.3 53.1±17.6 0.258
Causes Otitis media 3 (5.6) 1 (1.9) 2 (3.7)
Sinusitis 2 (3.7) 0 (0.0) 2 (3.7)
Dental infection 18 (33.3) 5 (9.3) 13 (24.1) 0.833
Penetration 12 (22.2) 8 (14.8) 4 (7.4) 0.003*
Lung infection 2 (3.7) 1 (1.9) 1 (1.9) 0.509
Heart infection 2 (3.7) 1 (1.9) 1 (1.9) 0.509
Isolated brain abscess 15 (27.8) 0 (0.0) 15 (27.8) 0.002*
Prognostic factors GCS≤12 15 (27.8) 8 (14.8) 7 (13.0) 0.043*
DM 8 (14.8) 2 (3.7) 6 (11.1)
IICP 17 (31.5) 3 (5.6) 14 (25.9) 0.191
Focal neurologic deficit 19 (35.2) 4 (7.4) 15 (27.8) 0.309
Seizure 9 (16.7) 3 (5.6) 6 (11.1)
Fever 7 (13.0) 4 (7.4) 3 (5.6) 0.177
Hematogenous 4 (7.4) 2 (3.7) 2 (3.7) 0.573
Contiguous 35 (64.8) 14 (25.9) 21 (38.9) 0.024*
Bacteremia 4 (7.4) 4 (7.4) 0 (0.0) 0.306

Values are presented as number (%) or mean±standard deviation.

GCS: Glasgow coma scale, DM: diabetes mellitus, IICP: increased intracranial pressure.

* p<0.05.

Table 2.
Imaging and pathogen findings of patients with brain abscess, with a statistical analysis of factors associated with their outcomes
Parameter Character Total (n=54) Death or disability (n=16) Cure (n=38) p-value
Location Frontal lobe 21 (38.9) 9 (16.7) 12 (22.2) 0.089
Parietal lobe 13 (24.1) 3 (5.6) 10 (18.5) 0.732
Temporal lobe 12 (22.2) 5 (9.3) 7 (13.0) 0.309
Occipital lobe 12 (22.2) 1 (1.9) 11 (20.4) 0.084
Basal ganglia 2 (3.7) 0 (0.0) 2 (3.7)
Cerebellum 2 (3.7) 0 (0.0) 2 (3.7)
Ventriculitis 4 (7.4) 4 (7.4) 0 (0.0) 0.006*
Size (cm) 3.1±1.3 3.2±1.2 3.0±1.3 0.716
Multiple 5 (9.3) 1 (1.9) 4 (7.4)
Pathogens No growth 12 (22.2) 5 (9.3) 7 (13.0) 0.309
Gram-positive cocci 29 (53.7) 8 (14.8) 21 (38.9) 0.723
Gram-negative bacilli 10 (18.5) 7 (13.0) 3 (5.6) 0.004*
Anaerobes 12 (22.2) 1 (1.9) 11 (20.4) 0.084
Fungus 2 (3.7) 0 (0.0) 2 (3.7)
Multiple 9 (16.7) 4 (7.4) 5 (9.3) 0.425
Operation Excision 1 (1.9) 1 (1.9) 0 (0.0) 0.152
Craniotomy 28 (51.9) 6 (11.1) 22 (40.7)
Stereotactic aspiration 25 (46.3) 9 (16.7) 16 (29.6)

Values are presented as number (%) or mean±standard deviation.

* p<0.05.

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