Diagnostic Challenges of Neurocysticercosis in a Non-endemic Country: A Case Report.

Neurocysticercosis (NCC) is the most common parasitic infection of the central nervous system worldwide and a leading cause of acquired epilepsy in endemic regions. In contrast, it is considered rare in developed countries such as Japan, where it is classified as a non-endemic region. Owing to increasing global migration, NCC is being encountered more frequently in non-endemic settings, where atypical clinical and radiological presentations often lead to diagnostic difficulty, particularly when parasitic structures are not pathologically identified. We report a case of NCC in a Nepalese immigrant in Japan with seizures and a solitary ring-enhancing brain lesion, diagnosed using established criteria in a non-endemic setting. A 31-year-old Nepalese man living in Japan presented with new-onset generalized tonic-clonic seizures. Neuroimaging revealed a solitary calcified intracerebral lesion in the right frontal lobe with ring enhancement and marked perilesional edema. No definite scolex was identified on imaging. Because the diagnosis remained uncertain, surgical resection was performed. Histopathological examination demonstrated an encapsulated cystic lesion with a three-layered architecture, but no definitive parasitic structures were identified. Microbiological stains were negative, and the Ki-67 labeling index was extremely low. Based on the Del Brutto diagnostic criteria, the patient fulfilled one major, two minor, and one epidemiological criterion, leading to a diagnosis of probable NCC. The postoperative course was uneventful, and no seizure recurrence or radiological relapse was observed during 12 years of follow-up. This case illustrates that NCC can present as a solitary ring-enhancing intracranial lesion without identifiable parasitic structures in non-endemic countries. A comprehensive diagnostic approach integrating clinical history, neuroimaging findings, epidemiological background, pathological features, and established diagnostic criteria is essential for appropriate diagnosis in such settings.