Atypical Presentation and Unexpected Resolution: The Role of Serial Cerebrospinal Fluid Analysis in Differentiating Bacterial and Viral Meningitis After Pituitary Surgery.

Viral meningitis can initially mimic bacterial meningitis, particularly in patients with a history of neurosurgical interventions. We report the case of a 34-year-old woman with a growth hormone (GH)/insulin-like growth factor 1 (IGF-1)-secreting pituitary tumor and multiple prior skull-base surgeries who presented with sudden-onset frontal headache. Initial cerebrospinal fluid (CSF) analysis revealed marked neutrophilic pleocytosis and elevated protein levels, prompting the initiation of empirical broad-spectrum antibiotic therapy. Despite this inflammatory profile, all cultures remained negative. Serial CSF examinations demonstrated a progressive decline in leukocyte counts with a shift toward mononuclear predominance, findings consistent with an evolving viral meningitis. Viral PCR was not available, so diagnostic interpretation relied on the clinical course and serial CSF analysis. Given the neurosurgical context and the favorable evolution of CSF parameters, antimicrobial therapy was discontinued, and antiviral treatment was maintained. Although no pathogen was identified, continuing antiviral therapy was clinically justified based on the CSF pattern and the patient's stable condition. She improved gradually without complications. This case highlights the importance of serial CSF analysis for clarifying meningitis etiology in high-risk postoperative patients and preventing unnecessary prolonged exposure to antibiotics.