Cryptic presentation: primary amoebic meningoencephalitis mimicking a high-grade malignancy resulting in surgical fatality within 48 hours. Illustrative case.

backgroundA 71-year-old male presented with weakness of the right upper limb and headache for the past 3 months. Brain magnetic resonance imaging (MRI) with contrast showed a left frontal space-occupying lesion, suggestive of a high-grade malignancy. Awake craniotomy with complete excision of the lesion was performed under immunofluorescence guidance. On postoperative day 2, the patient developed signs of meningoencephalitis and died. The histopathology report showed an abscess with parasitic infection, suggestive of primary amoebic meningoencephalitis (PAM), an infection caused by Naegleria fowleri. OBSERVATIONS: The patient presented with the above symptoms. Intraoperatively, the lesion exhibited fluorescence uptake and had a firm consistency. The patient did not exhibit any new neurological deficits during surgery, but on postoperative day 2, signs of meningitis emerged, and his condition deteriorated, ultimately leading to his death. LESSONS: PAM typically manifests with nonspecific symptoms of meningitis, progressing to a rapidly developing, severe form of meningitis that has a high mortality rate. The patient displayed obscure symptoms, and brain MRI revealed a space-occupying lesion with fluorescence uptake during surgery, suggestive of a high-grade malignancy. The diagnosis of PAM as a high-grade malignant space-occupying lesion was confirmed postmortem through histopathological analysis, a presentation considered exceedingly rare and unprecedented in the literature. https://thejns.org/doi/10.3171/CASE24358.