Parenchymal neurocysticercosis - A case report

Neurocysticercosis, caused by the eggs of Taenia solium, is the most common parasitic infection of the CNS in man, but is exceptional in Europe. Diagnosis is based on blood serum and CSF tests which are highly specific when positive. In doubtful cases neuroradiological investigation is particularly important. We describe a patient with parenchymal neurocysticercosis who was CSF negative, diagnosed and monitored during parasiticidal treatment by MR with a gradual resolution of symptoms until complete recovery and a progressive resolution of the neuroradiological parenchymal lesions. The cysticerci cycle produces interesting neuroradiological images related to its antigenic capacity. CT and MR scans with and without contrast administration are responsible for diagnosis and follow-up. The neuroradiological findings, which orientate diagnosis, are related to the various stages of infection in the brain tissue and include: presence of cystic lesions cyst content possible capsule with ring-like enhancement after contrast administration possible mural nodule, corresponding to the head of the parasite perilesional oedema with a mass effect. In the early stage (vesicular) the parasite is viable and appears as a mural nodule within a small cyst. MR shows a roundish fluid-filled lesion. The surrounding tissue shows no signs of inflammatory response due to failure to recognise the parasite as an antigen. In the second stage ("moribund" parasite) antigenic substances are released and an inflammatory response develops in the surrounding parenchyma with intense neovascularization and periparasitic contrast uptake. In the third stage (dead parasite) the lesion begins to degenerate with initial reparative gliosis resulting in a precipitation of calcium salts. Parenchymal neurocysticercosis respond well to drug therapy (praziquantel and, as alternatives, mebendazole or metriphonate) whereas the rarer forms of intraventricular, subarachnoid and mixed neurocysticercosis may require surgery. Both CT and MR are useful for diagnosis to identify the stage of infection and thus indicate the most appropriate treatment. Stage I lesions disappear after treatment, stage II cysts progress to the following stage whereas stage III indicates cell death and is the time when treatment is no longer beneficial.