Case Presentation: A 16 day old full-term male presented with 1 day of fever, irritability and poor feeding. Exam was significant only for irritability. Due to his age a sepsis evaluation was initiated. CBC demonstrated leukocytosis of 17,400 (58% polys, 26% lymphs, 14% mono), hgb 14.7 mg/dL, hct 43%, plts 556,000. CSF studies revealed pleocytosis with 3,379 WBC (81% PMN, 19% lymphs), 1,000 RBC, glucose 43 mg/dL, protein 113, no organisms on gram-stain, negative bacterial and viral culture, and PCR negative for HSV and enterovirus. Nine days into admission on IV antibiotics, MRI of the brain was obtained to assess for parameningeal infection as the focus of his culture-negative meningitis. MRI revealed a left parietal rim-enhancing lesion consistent with a brain abscess, which was subsequently drained by Neurosurgery. The patient completed 6 weeks of IV antibiotics. No organism was cultured from his blood, CSF, urine, or the abscess. Immunodeficiency work-up was normal. Final dx: left parietal brain abscess.

Discussion: Fever is a symptom of various disease processes and particularly in neonates it may be the only sign of significant underlying infection. Due to the immature nature of infants’ immune systems they are not able to limit the spread of infections between organ systems. For this reason, neonates and infants <90 days of age should undergo standardized evaluation when presenting with fever. When results of those studies are abnormal but do not yield a focus of infection, suspicion should shift to uncommon diagnoses. As part of this standardized work-up an LP should be performed. The analysis of CSF WBC count, glucose,  protein, gram stain and culture is used to determine the probability of CNS infection. As in our case, when faced with relatively normal glucose and protein levels but a highly abnormal CSF WBC count, suspicion should shift to a possible parameningeal infection. These infections typically arise from hematogenous seeding, direct extension of adjacent infection, or trauma. Clinical presentations vary which highlights the need for standardized work-up in a febrile infant. In general, MRI demonstrates a rim-enhancing lesion with high signal on diffusion weighted imaging when an abscess is present. Bacterial isolates are most commonly a single pathogen. For brain abscess in particular gram-positive cocci are found most commonly. Selection of antimicrobials with good intracranial penetration is key in the management of these infections as they can have devastating consequences if not treated appropriately.

Conclusions: Standardized work-up of the febrile neonate is critical in evaluating for possible infection. CSF studies should be a routine part of this evaluation. A CSF WBC count greater than 20-30 cells/uL is consistent with meningeal inflammation. When a patient presents with profound pleocytosis and culture negative studies, further investigation should be performed to identify a potential parameningeal focus of infection such as brain abscess, epidural abscess, or subdural empyema.