Otogenic Cerebellar Abscess with Polymicrobial Anaerobic Infection in a Young Female- A Rare Presentation

Abstract

Brain abscess is a serious clinical condition caused by a localized collection of pus within the brain tissue. This typically occurs as a result of an infection that originates from a nearby area, such as an ear, sinus, or dental infection, or an infection in the bloodstream. Streptococcus and Staphylococcus species are the most common organisms implicated in brain abscesses. Apart from aerobic growth, cases of mixed infections of both aerobic and anaerobic organisms are also commonly reported in the literature. Herein we report a 23-year-old immunocompetent female with chronic otitis media who presented with cerebellar abscess where the aerobic growth was sterile and anaerobic culture revealed pure growth of dual anaerobes viz… Peptostreptococcus and Bacteroides thetaiotaomicron. This case highlights the importance of prompt diagnosis and management of polymicrobial anaerobic infection in cases of brain abscess.

Introduction

Brain abscess is defined as a localized inflammation and infection of the brain parenchyma. Though mostly treatable, it warrants immediate medical attention because if left untreated, might result in severe morbidity and even mortality. The estimated incidence ranges from 1 to 2% in developed countries to approximately 8% in developing countries [1, 2]. Though there is no age predilection, it has been seen that more than 1/4th of cases are children and old-age groups [3]. It may involve aerobic or anaerobic bacteria and it may be single or polymicrobial. The sources of brain abscesses can be endogenous as well as exogenous. Endogenous sources can be through contiguous spread from nearby structures like ear infections, paranasal sinus, and dental infections or they may spread hematogenously, or from distant sources, as seen in cyanotic heart disease. Among exogenous sources, penetrating brain injury is the most common one [4]. Cerebellum and temporal lobe involvement have been seen in the case of the middle ear and mastoid infection [5]. Otogenic brain infections have been seen both in immunocompromised as well as immunocompetent individuals. A high index of suspicion, prompt diagnosis, and treatment remain the key. An abscess usually requires surgical drainage and the empirical antibiotics are started awaiting the final culture report. In the case of abscesses, anaerobes are often neglected as the diagnostic methods are tedious. In cases of brain abscesses, mixed growth of aerobic as well as anaerobic organisms is usually obtained [6]. However, in the following case report, the authors present a case of otogenic cerebellar abscess complicated by dual anaerobic infection only i.e. by Peptostreptococcus and Bacteroides thetaiotaomicron and interestingly there was no aerobic organism obtained.

Case Report

A 23-year-old female presented to emergency with complaints of headache along with intermittent pus discharge from the left ear for the last five days and altered sensorium since 1 day. She was a known case of left chronic suppurative otitis media (CSOM) for the last year and was under treatment for the same from outside but was non-compliant. On examination, she was unconscious with a Glasgow Coma Scale of 6/15. A plain and contrast-enhanced CT scan of the brain revealed a left cerebellar abscess with a mass effect on the 4th ventricle and brainstem (Fig. 1). In view of the comatose state and herniation, she was taken up for abscess drainage urgently without waiting for MRI. Approximately 30 cc foul-smelling purulent fluid was drained and sent to the microbiology laboratory for aerobic as well as anaerobic culture. She was started on broad-spectrum antibiotics for gram-negative, and gram-positive bacteria along with metronidazole for anaerobic coverage. For aerobic culture, 5% sheep blood agar and MacConkey agar were used whereas for anaerobic culture, Robertson’s cooked meat (RCM) broth along with freshly prepared sheep blood agar was used. After the application of a heavy inoculum on the primary plate, a metronidazole disc (5 μg) was placed at the center and the plate was incubated for 48 h at 37 °C in an anaerobic jar using an automated anaerobic gas generation system (Anoxomat Mart II, Mart Microbiology BV, Lichtenvooorde, Netherlands). The anaerobic environment was created from the gas mixture (80% N₂, 10% CO₂, 10% H₂). The pus from the left ear and drain from the cerebellar abscess was also sent to the laboratory. Grams stain and Ziehl Neelsen staining for acid-fast bacilli were also performed. Grams stain from both samples showed the presence of pus cells, Gram-positive cocci arranged in chains, and Gram-negative bacilli. Staining for acid-fast bacilli (AFB) was negative. The aerobic culture was sterile after overnight incubation in both samples. Since the Gram stain was positive for both gram-negative bacilli and gram-positive cocci, with no growth obtained on aerobic culture, there was a suspicion of anaerobic infection for which the patient was already started on intravenous metronidazole. The patient succumbed to sepsis and brain herniation in the next 48 h.

Fig. 1.

Contrast-enhanced CT scan showing left cerebellar abscess

Meanwhile, after 48 h of anaerobic incubation, the anaerobic culture of brain abscess sample showed the growth of Peptostreptococcus anaerobius, Peptostreptococcus asaccharolyticus, and Bacteroides thetaiotaomicron confirmed by MALDITOF (Biomerieux) with score 99.9 and all were sensitive to metronidazole. Similarly, the anaerobic culture of the pus from the left ear showed the growth of Peptoniphilus lacrimalis and Bacteroides thetaiotaomicron again confirmed by MALDITOF (Biomerieux) with a score of 99.9 and sensitive to metronidazole.

Discussion

With the increase in the prevalence and better identification of anaerobic infections due to the advent of MALDI-TOF MS, the etiology of brain abscesses has significantly changed [7]. However, the anaerobic organisms are often neglected and not isolated routinely due to unavailability as well as tedious requirements of anaerobic culture methods. V Lakshmi et al. in a study have reported an incidence of brain abscess as 25% among patients with space-occupying lesions [8]. The colonized bacteria of the oral and upper respiratory tract (Bacteroides spp, Fusobacterium spp, Prevotella spp, and the anaerobic Streptococci) causing ear or sinus infection can spread upto the brain and lead to abscess formation. Brain abscesses can involve all age groups from infancy to the elderly and earlier studies also showed a wide range of variation [1, 2, 8–10]. CSOM continues to be the most frequent predisposing condition in all age groups. Previous literature also documented that in 31–49% of cases of brain abscess, CSOM is a major source [8, 11]. Although middle ear infection is mainly seen to extend to the temporal lobe or cerebellum [2, 12]. Multiple otogenic abscesses can also involve the frontal and parietal lobes [8], probably due to arterial dissemination of infective emboli. In the present case scenario, CSOM was present in the left ear for the last year, and the left cerebellar abscess was there on the NCCT head, highlighting the otogenic source of the brain abscess.

Etiology of brain abscess involves both aerobic (Enterobacteriaceae, Streptococcus spp., and S. aureus) as well as anaerobic (Clostridium spp, Bacteroides spp., and Peptostreptococcus spp.) [13, 14]. Previous literature shows B. fragilis and Peptostreptococcus spp. as the commonly isolated anaerobes in brain abscesses [2, 3, 13]. In our case also, both the samples i.e. pus from left ear as well as drain from cerebellar abscess showed growth of Peptostreptococcus and Bacteroides thetaiotaomicron. Monomicrobial anaerobic infection is more common than polymicrobial and aerobic is more common than anaerobic in brain abscesses [2, 13, 14]. Menon S et al. [2] documented similar findings in brain abscesses as monomicrobial anaerobic flora in 16%, mixed aerobic and anaerobic bacteria in 4% of patients, and polymicrobial anaerobic flora in 1.33%. In the present case, we have found only polymicrobial anaerobic growth as the aerobic culture was sterile. V Lakshmi et al. also documented an increased occurrence of polymicrobial anaerobic abscesses [8]. In various studies, 13.7–17% of patients with brain abscesses have anaerobic bacterial pathogens [2, 3, 10]. Isolated polymicrobial anaerobic growth could be explained by the phenomenon of bacterial synergy between anaerobic organisms which is associated with increased virulence, due to enhanced bacterial growth in dual infections [15]. However, due to various limitations in culturing anaerobic organisms, the prevalence of anaerobic bacteria in brain abscesses can be influenced. History of CSOM should be enquired in all the cases of brain abscess. While managing CSOM, anaerobic organisms must be taken into consideration, and metronidazole should be initiated as an empirical antibiotic therapy [16]. It was previously thought that the common pathogens of CSOM are Staphylococcus aureus and Gram-negative organisms mainly Pseudomonas aeruginosa. However, in a review on CSOM, in North America and Indonesia, anaerobes were identified in about 50% of cultures [17], out of which the most common were Peptostreptococcus species, anaerobic Gram-negative bacilli, and Fusobacterium nucleatum. [17]

Due to the tedious procedure of anaerobic culture, the role of anaerobic organisms in brain abscesses is usually neglected. Based on the presumptive source of infection and gram stain results, prophylactic antibiotic coverage should be provided. As metronidazole has a wide spectrum of action against anaerobes and excellent CSF penetration, it is the drug of choice for abscesses. With an increase in resistance towards metronidazole among anaerobic organisms failure of therapy has been seen in some cases. Our patient was given metronidazole post-operatively, but it could not save the patient, the scenario might be different if it would have been initiated early. However, resistance to metronidazole in Bacteroides thetaiotaomicron is on a rising trend in many cases [18]. Even though metronidazole was started post-operatively in this case, there might be a probability that Bacteroides might have resistance to metronidazole, thereby proving to be ineffective. One limitation was that the antimicrobial sensitivity of the isolate could not be performed due to a lack of facilities. Thus early investigation and management in case of anaerobic brain abscess could be a game changer.

Conclusion

Brain abscess is a critical clinical condition, so a high index of clinical suspicion followed by appropriate microbiological investigations that should include both aerobic as well as anaerobic along with prophylactic metronidazole will help in the better prognosis of patients with brain abscess. Proper management of CSOM patients should be done to prevent the occurrence of otogenic brain abscesses.

Funding

None.

Declarations

Conflict of Interest

NA.

Patient’s Consent

Informed written consent was obtained from the patient’s relative, her husband.