First report of adult Taenia solium in human brain with neurocysticercosis: illustrative case.

backgroundThis report presents the first documented case of a live, adult Taenia solium tapeworm discovered within the human brain-a finding that challenges the conventional understanding of neurocysticercosis (NCC), a parasitic disease typically caused by larval cysts. OBSERVATIONS: A 54-year-old woman with a history of breast cancer presented with seizures, headaches, and photophobia. Initial suspicion of a metastatic brain tumor led to serial MRI studies, which revealed a migrating lesion in the right temporal lobe. During craniotomy, a motile helminth was surgically excised from the brain parenchyma. Histopathological analysis confirmed that the organism was an adult T. solium tapeworm, with taeniid eggs identified within the specimen, marking the first evidence of intracranial adult taeniasis and ectopic cerebral oviposition. The patient's prior oncological treatments, including mastectomy and postoperative therapies, raise hypotheses about immune or anatomical changes facilitating parasitic neuroinvasion. LESSONS: The discovery underscores critical gaps in diagnostics, as the lesion mimicked metastatic cancer radiologically, and therapeutics, as standard cysticidal drugs target larval stages, not adult worms. This report highlights the urgent need to investigate interactions between parasitic infections and oncological interventions. It calls for updated clinical guidelines to address this novel pathogenic mechanism and emphasizes the importance of integrating parasitological expertise into neurological care. https://thejns.org/doi/10.3171/CASE25370.