PCR-Confirmed Convexity Subarachnoid Neurocysticercosis with Negative Serology: A Case Report.

Extraparenchymal neurocysticercosis, caused by Taenia solium, is an uncommon form of neurocysticercosis involving the subarachnoid space and ventricular system. Clinical manifestations are heterogeneous, including seizures, meningitis, and intracranial hypertension, and are often associated with worse outcomes. Diagnosis remains challenging, as cysts may be difficult to detect on conventional imaging due to signal characteristics similar to cerebrospinal fluid, frequently leading to inconclusive results. We describe a patient presenting with a six-month history of focal seizures in whom the diagnosis was established following surgical excision of a cystic lesion, with definitive confirmation provided by positive PCR detection of T. solium nuclear ribosomal DNA in the excised tissue. The patient received 14 days of dual antiparasitic therapy and remained free of neurological symptoms during 12 months of follow-up. This case highlights the potential limitations of noninvasive diagnostic modalities and the challenges that physicians might encounter when evaluating infectious diseases that are not endemic to their country of practice. It also underscores the value of a structured diagnostic approach, as recommended by several international health bodies, complemented by advanced molecular techniques such as PCR. Overall, it provides a clinically relevant illustration of key diagnostic challenges and decision-making steps in the evaluation of this complex condition.