Indian Journal of Pathology and Microbiology

: 2014  |  Volume : 57  |  Issue : 1  |  Page : 160--161

Pneumocephalus in mixed aerobic and anaerobic (Bacteroides fragilis) meningitis

Subasree Ramakrishnan1, Pramod Krishnan1, P Satish Chandra1, HB VeenaKumari2, S Nagarathna3,  
1 Department of Neurology, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
2 Department of Neuromicrobiology, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
3 Srichitra Institute of Medical Sciences, Trivandrum, Kerala, India

Correspondence Address:
Subasree Ramakrishnan
National Institute of Mental Health and Neurosciences, Bengaluru - 560 029, Karnataka

How to cite this article:
Ramakrishnan S, Krishnan P, Chandra P S, VeenaKumari H B, Nagarathna S. Pneumocephalus in mixed aerobic and anaerobic (Bacteroides fragilis) meningitis.Indian J Pathol Microbiol 2014;57:160-161

How to cite this URL:
Ramakrishnan S, Krishnan P, Chandra P S, VeenaKumari H B, Nagarathna S. Pneumocephalus in mixed aerobic and anaerobic (Bacteroides fragilis) meningitis. Indian J Pathol Microbiol [serial online] 2014 [cited 2022 Jul 5 ];57:160-161
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Full Text


Less than 100 cases of Bacteroides meningitis have been reported so far, primarily in the pediatric population. [1] Only very few adult cases of pneumocephalus have been reported with meningitis.

A 50-year-old male patient, native of Nepal presented with low grade fever and left hip pain of 4 months duration. A week prior to admission he developed high grade fever, headache. He was emaciated, toxic, had left inguinal lymphadenopathy, flexion deformity of left hip and pedal edema. He was conscious yet, irritable and had neck rigidity.

Computed tomography brain showed bilateral frontal pneumocephalus with streaks of gas throughout the brain parenchyma [Figure 1]. Cerebrospinal fluid (CSF) was with high opening pressure, turbid, yellow green foul smelling with protein level of 2292 mg/dl and glucose of <10 mg/dl. Cell count was not possible. Gram staining revealed plenty of pus cells and thin pleomorphic, non-sporulating Gram-negative bacilli. No acid fast bacilli or fungal elements were seen. Culture yielded non-hemolytic streptococci aerobically, but grew Bacteroides spp anaerobically. Tubercular and fungal culture of CSF were negative.{Figure 1}

He had microcytic anemia with Hb of 7.5 g/dl and thrombocytosis. Chest skiagram showed bilateral apical haziness, reticulonodular pattern, hilar lymphadenopathy and crowding of ribs on the left side suggestive of consolidation superimposed on pre-existing pulmonary tuberculosis [Figure 2]. Human immunodeficiency virus 1 and 2 was negative.

Patient was provisionally diagnosed to have mixed pyogenic meningitis and was initiated on meningitic doses of ceftriaxone, metronidazole and amikacin parenterally for 3 weeks, followed by oral metronidazole for 8 weeks. He showed improvement in alertness within 2 days of starting antibiotics. Patient continued to improve satisfactorily.{Figure 2}

CSF analysis was repeated 2 weeks later and it showed protein content of 660 mg/dl, glucose of 42 mg/dl, plenty of pus cells and 1120 cells/mm 3 , 70% polymorphs, 25% lymphocytes and 5% monocytes. Gram stain, aerobic and anaerobic cultures of blood and CSF were negative. Repeat contrast enhanced computed tomography brain showed resolution of the pneumocephalus. He was advised to continue oral metronidazole for a total of 8 weeks.


Brain abscesses and subdural empyema are the most common anaerobic infections of the central nervous system, whereas anaerobic meningitis is rare and is usually related to parameningeal collection or shunt infection. [2] Anaerobic meningitis was identified for the first time in India by Chandramukhi and Rama Devi. Bacteroides fragilis was the predominant cause of the encountered 18 cases. [3] When B. fragilis meningitis occurs in adults, there is often an underlying cause such as cholesteotoma, nasopharyngeal carcinoma, chronic otitis media, systemic infection. Our patient had a chronic pulmonary and joint infection, probably of tubercular etiology.

Diagnosis relies on presumptive evidence and gram staining. Bacteroides identification relies on culture. Newer techniques such as 16S ribosomal ribonucleic acid gene sequence analysis are more reliable in species-level identification. The first adult case of pneumocephalus in meningitis in a mixed aerobic-anaerobic infection was described in 1985. [4] So far, only one case report of pneumocephalus in B. fragilis in an adult case is reported in the literature as we are aware. [5]

Cure rates of cure of >80% are reported. Metronidazole, β lactam/lactamase inhibitor combinations, and carbapenems are preferred. A high index of suspicion and appropriate microbiological techniques are necessary for the diagnosis.


Dr. Chandramukhi A.


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