Clinical profile of brain abscesses: ten-year retrospective single-center study

Introduction

A focal suppurative process of the brain parenchyma is a brain abscess.¹ Brain abscess is brought on by bacteria, mycobacteria, fungus, protozoa, or helminths in the parenchyma of the brain which can develop from contiguous (sinusitis, mastoiditis, odontogenic infection, dental infection) or from distant sources of infection like endocarditis, congenital heart disease, respiratory infections, etc.² The clinical manifestations of brain abscess depend upon its size, location, number, and any secondary brain injury. Patients with brain abscesses commonly present with headache, neurological deficits, fever, and altered sensorium. Although serum markers can be detected in up to 75% of cases and raise a significant amount of clinical suspicion, the primary diagnostic techniques used today are imaging modalities.³ In developing countries, brain abscesses occur at a rate of about 8% of intracranial masses, compared to 1-2% in Western nations.⁴

Methods

This study was ethically approved by the institutional review committee of Chitwan Medical College recognized by Nepal Health Research Council (Ref: CMC-IRC/070/080/16). This is a retrospective study achieved by reviewing medical records from ten years (April 2013 to April 2023). Data were searched from the electronic data record system of the neurosurgery ICU, operation records, and hospital records. Both electronic and record books were reviewed in the process of data collection. All cases admitted to our tertiary care center with the diagnosis of brain abscess were included in this study. We found 20 cases diagnosed in our tertiary care center upon reviewing the medical records. Among those 20 cases, 18 cases are included in this case series whereas two cases were excluded due to inadequate data on our records. For each case, information about the patient’s demographics, clinical presentation, initial neurological status (clinical signs associated with GCS, seizures, focal neurological deficits), risk factors, site of lesion, Source of infection, radiological and microbiological test results, and treatment modalities was reviewed. At the time of discharge, the result was evaluated using the GOS. Moderate disability (having an impairment but being independent) and good recovery were considered favorable outcomes. Death, chronic vegetative state, and severe disability (aware but disabled) were all considered unfavorable outcomes.

All the related data were filled in preformed proforma and entered in SPSS version 26.0 for analysis. Data were analyzed using frequency, mean, and proportion functions.

Results

Between April 2013 to April 2023, 20 cases of brain abscesses were admitted and treated in our tertiary care centre. Among those 20 cases 18 cases are included in this case series, two cases were excluded due to inadequate data on our records. Among 20 cases of brain abscess, 14 were males and four were females with ratio of 3.5:1. The mean age is 24.6 years with a maximum age of 68 years and minimum age of ten months. Ten cases were of less than 18 years old, and eight cases were of more than 18 years. 50% of cases stayed in the hospital for <20 days.

The classical triad of brain abscess viz. fever, headache, and focal neurological deficit is present in 16.67% (n=3) of the cases. Fever (61.1%) and headache (50%) are the most common presentation followed by focal neurological symptoms (33.3%), ear discharge (33.3%), and vomiting (33.3%) whereas seizure was present in only 16.7 % of cases. Presenting symptoms of all cases are summarized in (Table 1). Consciousness was clear (GCS=15) in five patients (27.7%), mildly disturbed (GCS=13 or 14) in 3 (16.7%), moderately disturbed (GCS=9-12) in 8 (44.5%), and severely disturbed or comatose (GCS=3-8) in 2 (11.11%) patients.

In 88.8% of patients, the abscess was localized in a single location with the temporal region being the most commonly involved region in 27.8% of patients whereas 11.1% of patients had abscesses in multiple locations. Primary focus of lesion was identifiable in 55.56% (n=10) cases with CSOM being the most common focus of infection and in 44.4% of patients, the source of infection was unknown. One out of 18 cases was culture positive in which proteus mirabilis was isolated.

In 72.2% (n=13) patients craniotomy and evacuation was done and burr-hole and evacuation were performed in 11.1% (n=2) patients, whereas 16.7 % (n=3) patients denied treatment.

Of the 18 patients in the study, 5.56% patient died (GOS=1), 11.1% had moderate disability (GOS=4) and 66.7% (GOS=5) had good outcomes whereas GOS cannot be designated to 16.7% of individuals who denied intervention.

Discussion

In this study, we included 18 cases of brain abscess which has fever as the most common presenting complaint and mostly involves the temporal lobe of the brain with chronic ear infection being the most common foci of infection.

The mean age of the patient is 24.6 years with male predominance with a ratio of 3.5:1. A case series from Nepal⁵ also suggests brain abscess had male predominance with a ratio of 2.1:1 and most of the other studies also report the same finding.^3,6 whereas it is different in a developed country like Germany with an equal predisposition in both male and female populations.⁷ In a study, Landriel reported 59.3% of the female population in the study had brain abscesses.⁸ With a mean age of 24.4 years, our study has 55.5% of the younger population involvement (age less than 18 years). A previous study from Nepal also showed similar age group involvement with a mean age of 16.76 years.⁵ One of the reasons for the maximum involvement of the younger age group is the prevalence of predisposing factors like ear infections, odontogenic, and sinusitis in the younger population.⁹

Chronic suppurative otitis media (CSOM) is the most common contagious source of infection present in most of the studies.^3,5,10 Whereas a study from Germany reported sinusitis and dental infections as the most common source of infection.⁷ The source of infection and location of the brain abscess was found to be closely related. The most common location of the brain abscess was found to be the temporal lobe or cerebellum if the source of infection is CSOM whereas frontal lobe involvement is most common where sinusitis and dental infections are most common.^3,5,7,11,12 The classical triad of brain abscess viz. fever, headache, and focal neurological deficit is present in three patients. Fever is complained by 61.1 % of the patient followed by headache which was the chief complaint of 50 % of the patient. Previous studies suggest both headache^3,5,7 and fever¹⁰ as the major presenting complaint whereas the triad of brain abscesses is present in only 20% of cases.⁶ One of our cases had an increase in head circumference as a chief complaint who was ten months old. There have been reports of increased head circumference as the presenting complaint in younger age groups.^9,13

The use of intravenous antibiotics and drainage or excision of abscesses is the treatment of choice for brain abscesses.¹⁴ However, the treatment varies according to the size, location, and stage of the abscess. Surgical procedures used are burr hole and evacuation, craniotomy, craniectomy, evacuation or excision, and stereotactic CT/MRI-guided aspiration.¹⁴ Stereotactic CT-guided aspiration is one of the most effective minimally invasive methods available for the aspiration of abscesses. A study suggests this method of treatment can access the abscess located in inaccessible regions like the thalamus, and brain stem, and in case of multiple abscesses.^15,16 Stereotactic aspiration has its own set of complications and drawbacks. Most of the cases need repeated aspiration and constant monitoring by repeated CT scans and there are risks of complications during the procedure like the risk of rupture of abscess into the ventricle, subarachnoid leakage of pus and ventriculitis, or meningitis.^17,18 Whereas in open craniotomy since there is extensive resection and drainage of the abscess there is a rate of low recurrence.¹⁹ In the cases with subdural empyema open craniotomy and drainage is still the treatment of choice.²⁰ However, aspiration has a higher mean survival rate compared with open excision of brain abscesses.²¹ In our study, 15 patients had surgical intervention which includes craniotomy and burr hole with the evacuation of the abscess, whereas three patients denied any form of intervention.

Isolation of organisms causing brain abscesses is difficult and most of the reports were culture negative. In our study, only one case (5.5%) was found to be culture positive with Proteus mirabilis as the causative agent. Similar reports were reported by Kafle et al.⁵ with only 19.61% of the cases showing positive culture. The reason for these negative culture reports may be the preoperative use of antibiotics and limited lab facilities lacking an anaerobic culture medium.²² Decreased GCS at the time of presentation has been associated with poor outcomes in patients with brain abscesses.¹⁰ The mortality rate in our study was 5.55% whereas other studies from Nepal, China, Pakistan, and Germany showed mortality rates of 3.92%, 16.9%, 11.3%, and 23.4% respectively.^3,5,7,10

Limitations of this study

This study has a small sample size. It is a single-center study and cannot represent the profile of brain abscesses throughout the country and the result cannot be generalized for the whole population. In the future, multicentre prospective studies must be planned for determining the risk factors and outcome of the patient with brain abscess.

Conclusion

Brain abscess is an uncommon but important clinical condition as the mortality rate is high if timely intervention is not done. In this series, we presented cases of brain abscesses in the past ten years who were treated in our tertiary care center. CSOM being one of the most common foci of infection, multidisciplinary management with an otorhinolaryngology team will be the way forward for better outcomes of cases with brain abscesses.