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Special Feature
March 1998

Radiological Case of the Month

Arch Pediatr Adolesc Med. 1998;152(3):298. doi:
Denouement and Discussion: Neonatal Brain Abscess Caused by Citrobacter diversus

Figure 1. Two axial computed tomographic scan sections of the brain with intravenous contrast enhancement show several large abscesses in the left parietal cortex. The walls of the abscess cavities are actively enhancing, indicating vascular leak. Midline shift reflects the increased volume of the left hemisphere.

Figure 2. A computed tomographic scan after the completion of 10 weeks of antibiotic therapy shows complete resolution of the abscesses and normal brain parenchyma with no shift of the midline.

The cranial computed tomographic scan showed several large brain abscesses in the left parietal cortex and diffuse edema. The 2 largest abscesses were drained and 70 mL of a malodorous pus was evacuated. The abscess culture was positive for Citrobacter diversus. A therapeutic regimen of intravenous antibiotics (gentamicin sulfate, cefotaxime sodium, and metronidazole) and phenobarbital sodium was started. During the next 2 days, the abscesses were locally irrigated with a gentamicin solution. An electroencephalogram, performed the day after admission to the hospital, showed generalized slow background activity, without focal abnormalities or epileptic activity.

Additional predisposing factors are congenital heart disease with right-to-left shunt, otitis and rhinosinusitis, cystic fibrosis, immunosuppression, penetrating head injury, and prematurity.1 The physiological right-to-left shunt of the neonatal blood circulation can explain bacterial colonization of the brain during an incident of septicemia.

Citrobacter diversus is a gram-negative enteric bacterium found in the gastrointestinal tract or the female genitourinary tract. It is pathogenic in immunocompromised patients and neonates, in whom it causes a rare but devastating meningitis. Most of these patients will develop brain abscess and approximately one third will die of the disease.2

The pathogenesis of C diversus brain abscess in neonates is unknown. Specific features characterize C diversus infection. Citrobacter species appear to possess invasive capability to enter brain parenchyma related to cerebral vasculitis, subsequent infarction, then bacterial invasion of necrotic tissues.3 Bacterial resistance to phagocytosis or intraphagocytic killing may also play a role. Evidence derived from an infant rat model suggests that strains of C diversus, with a 32000–molecular weight outer membrane protein, produce different histopathologic brain changes from those produced by strains without this protein.4

Intravenous antibiotic therapy was continued for 6 weeks. At that time no contrast enhancement was seen in the residual brain abscesses. After discontinuance of intravenous antibiotic therapy, oral amoxicillin therapy was administered for 4 weeks.

A computed tomographic scan after the discontinuance of the antibiotic regimen showed no residual brain abscesses (Figure 2). On neurological examination at the age of 6 months the infant demonstrates generalized hypertonia. He sits alone at the age of 61/2 months.


A brain abscess in a neonate is uncommon and associated with high risk of severe neurological sequelae or death. Abscesses are caused by hematogenous spread of gram-negative bacteria including C diversus, Proteus species, and Serratia marcescens.5

Approximately 1% of neonates with meningitis develop a brain abscess.6 This complication should be suspected in case of persistent fever or cerebrospinal fluid pleocytosis, even without a positive blood or cerebrospinal fluid culture, or in infection by an unusual organism such as C diversus. Venous thrombosis is hypothesized to cause necrotizing vasculitis and ischemia, leading to brain necrosis. The necrosis is identified as the major predisposing factor for bacterial implantation and localized cerebritis, the first stage in development of a brain abscess.7 Cerebral necrosis is a characteristic feature of Proteus and Citrobacter species infection.

Optimal therapy of resulting brain abscesses remains controversial. The recommended antimicrobial agents are third-generation cephalosporins, aminoglycosides, and trimethoprim and sulfamethoxazole.8 Appropriate antimicrobial susceptibility tests are needed. Prolonged antibiotic treatment, for a minimum of 4 weeks, is recommended. There are recent reports of C diversus resistant to gentamicin and third-generation cephalosporins, and in these cases imipenem and cilastin sodium therapy is suggested.9 Surgical aspiration or drainage of an abscess is considered, especially in the case of one isolated abscess. Rosenblum et al10 consider the size of the abscess on computed tomographic scan an important prognostic factor for resolution with medical therapy alone. A brain abscess with a diameter ranging from 2 to 6 cm needs a combination of surgical intervention and long-term antibiotic treatment.10,11

Accepted for publication February 20, 1997.

Reprints: Philippe Alliet, MD, Department of Pediatrics, Virga Jesse Hospital, Stadsomvaart 11, 3500 Hasselt, Belgium.

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