The average age of the study participants was 52 years, and 56.14% of them were aged between 40 and 60 years. There are inconsistent reports of the age predilection of brain abscess. Some studies show that individuals older than 40 years are more susceptible to brain abscess[4, 7, 8], whereas others show that brain abscess occurs more often in individuals younger than 40 years[9, 10]. The average age of participants in a meta-analysis conducted in 2014 was 33.6 years. Therefore, the age group that is most affected is difficult to determine, and it may depend on the underlying predisposing factors for brain abscess. Moreover, we found that regardless of age, men were more susceptible to brain abscess than women, with a ratio of 2.8:1. Other authors have reported similar findings[7, 11], although a female predilection was observed in one of these studies. Headache, fever, and hemiplegia were the most common symptoms in our study, occurring in 52.63%, 45.61%, and 45.61% of the patients, respectively; this was consistent with previous reports[1, 8, 12]. Headache, fever, and focal neurological deficit are regarded as the classical symptoms of brain abscess. However, few patients experience all three symptoms simultaneously. In our study, the classical triad of headache, fever, and hemiplegia was only observed in eight patients (14.04%); this was lower than the previously reported rate of 20%. The presentations were insidious and atypical, and the absence of this classical clinical triad decreases the likelihood of brain abscess being suspected on initial examination.
Here, 42.11% of the patients had some predisposing factor, and 22.81% (13 patients) had adjacent site infection, including paranasal sinusitis, chronic otitis media, mastoiditis, and dental infection. A previous study in a developing country found that otitis media was the most common source of intracranial suppuration. However, this was not the case in our study, possibly due to improvements in the treatment of otitis media in recent decades. It is important to recognize predisposing factors because eliminating the underlying infection helps to avoid prolonged infection. Comorbidities, including diabetes mellitus, tumor, liver cirrhosis, and granulocytopenia, were noted in 24.56% of the patients in our study. Other comorbidities, including human immunodeficiency virus infection, autoimmune disease, and immunosuppressive therapy, were reported in a previous study. However, none of our patients had these comorbidities, and diabetes mellitus was the most common comorbidity observed in this study. The relationship between diabetes mellitus and susceptibility to infection has been reported. Impaired glucose control may affect host defense and increase the risk of brain abscess.
Only half of the patients in this study had an elevated peripheral white blood cell count. Indicators of inflammation such as white blood cell count, erythrocyte sedimentation rate, and C-reactive protein level play a limited role in the diagnosis of brain abscess. An increased cell count in the CSF, which indicates leptomeningeal affection, was found in 94.44% of the patients who underwent lumbar puncture in this study, and this finding helped us determine the nature of the brain lesion in those patients. However, not all patients with brain abscess show leptomeningeal involvement, and the role of lumbar puncture in its diagnosis is limited. Moreover, lumbar puncture should be performed with caution. There are reports of clinical deterioration after lumbar puncture due to exacerbation of the brain tissue shift caused by the brain abscess, which may lead to death. The rate of CSF culture positivity in our study was 25%, which is similar to the rate of 24% reported in a previous study. Therefore, it is difficult to determine the causative organism solely based on the result of CSF culture.
The rate of pus culture positivity in our study was 46.15%, which is far lower than the previously reported rate of approximately 70%[1, 13]. This may be because we initiated antibiotic therapy before obtaining samples for culture, and the standard culture protocol followed at our hospital may result in certain organisms going undetected. The use of next-generation bacterial sequencing may help to identify more pathogens. In our study, gram-negative enteric bacteria were the most common pathogens observed in pus, and ceftriaxone, which is effective against gram-negative bacteria, was often initially administered as empirical antibiotic therapy. In previous studies, the most commonly observed bacteria in patients with brain abscess were those of the streptococcus species. However, various pathogens, including staphylococci, gram-negative enteric bacteria, and fungi, have been isolated from brain abscess specimens[1, 13]. Moreover, a previous study reported the frequent occurrence of the gram-negative enteric bacteria Klebsiella pneumoniae in Asian patients; it caused 10% of all brain abscesses in Taiwan. Multiple abscesses due to Klebsiella pneumoniae are often found in organs such as the brain, liver, and lungs, especially in patients with diabetes mellitus or liver cirrhosis. In our study, Klebsiella pneumoniae was found in the pus of four patients, and one patient with diabetes had comorbid liver abscess.
The most common brain abscess location in our study was the frontal lobe, followed by the temporal and parietal lobes, and most of the patients had single lesions. This result is consistent with a previous report[1, 7]. However, another study found that the temporoparietal region is the most common brain abscess location. The location of a brain abscess partly depends on the route of infection transmission. Paranasal sinusitis is often associated with a frontal lobe abscess and otitis media and mastoiditis are associated with temporal lobe or cerebellar abscesses.
Here, 54.39% of the patients underwent surgery. Most of them underwent stereotactic drainage, while others underwent craniotomy. The rate of surgical treatment was lower than that reported previously, (60–87%)[1, 7, 8]; the reason for this is unclear. Further research is needed to determine the reason for this difference. Although craniotomy was once thought to be associated with lower recurrence and mortality rates than stereotactic drainage, with increasing availability of computed tomography, the difference between craniotomy and stereotactic drainage has become uncertain. A previous study found no difference in the effects, outcomes, and complications of these two surgical techniques. Even after surgical treatment, long-term antibiotic therapy (4–8 weeks) was necessary. Moreover, 75.44% of the patients in our study had a good outcome, and only two patients died. The mortality rate, which was approximately 8–53% before 2014, has decreased in the recent decades, and it has been reported as 4.3% in 2018. The mortality rate in our study was lower than that in previous studies. We believe that this may reflect improvement in the treatment of brain abscess, although selection bias related to patient recruitment from our hospital, which is a tertiary hospital, should be considered. Previous studies have reported inconsistent findings regarding the factors associated with outcome. Landriel et al. found that age, immunosuppression, and hematogenous spread were associated with a poor outcome. Zhang et al. revealed that gender was associated with an unfavorable outcome. Another study found that consciousness at presentation had prognostic value. Nevertheless, our findings indicate that headache, and not confusion, age, adjacent site infection, or type of surgery, influenced outcome. As a classical symptom of brain abscess, headache indicates possible intracranial hypertension, which may lead to a poor outcome.
This study has several limitations. First, the sample size was small. Second, it was a retrospective, single-center study. Consequently, our findings may not be generalizable to patients in different regions, and some data, including inflammatory marker levels, could not be collected and analyzed. Multicenter studies with larger samples should be conducted in the future.