Late-onset Streptococcus pneumoniae brain abscess following cystoperitoneal shunt placement for an arachnoid cyst: illustrative case

BACKGROUND Brain abscesses represent a focal intracranial infection characterized by the localized accumulation of pus within a vascularized capsule. While typically occurring in immunocompromised patients, they may also present in otherwise healthy individuals. CSF shunt-related infections commonly manifest as meningitis or ventriculitis; however, brain abscess formation remains rare, particularly with unusual pathogens and extended latency. OBSERVATIONS The authors present the case of a 58-year-old female patient who developed a Streptococcus pneumoniae brain abscess 7 years after cystoperitoneal shunt placement for an arachnoid cyst. She presented with headaches and altered consciousness, but without systemic infection signs. Radiological studies identified a left frontal abscess adjacent to the shunt catheter, which was initially considered either a tumor or an abscess due to the delayed onset. Surgical drainage, complete shunt removal, and targeted antibiotic therapy led to complete symptom resolution without residual neurological deficits. No subsequent shunt placement was required. LESSONS Clinicians should be aware of the potential for late-onset brain abscesses associated with CSF shunts, even several years after placement. This case highlights the importance of careful consideration regarding the necessity of shunt placement in asymptomatic patients with arachnoid cysts and the need for vigilant monitoring for rare infectious complications. https://thejns.org/doi/10.3171/CASE25547