Cysticercosis

            Neurocysticercosis is the most frequently encountered parasitic infestation of the CNS. Originally endemic in underdeveloped countries, predominantly Latin America, Africa, Asia and some portions of eastern Europe, it is becoming increasingly frequent in North America in immigrant populations. Humans become accidental hosts for the larval stage of Taenia Solium, the pork tapeworm, by ingesting contaminated material. The eggs hatch in the stomach and larvae burrow through the gut wall and become distributed by the circulatory system. There is a predilection for involvement of the brain. Patients most often present with seizures, elevated intracranial pressure, focal neurologic abnormalities and altered mental status. Asymptomatic infections are common.

            Four forms of neurocysticercosis are described: meningeal, parenchymal, ventricular and mixed. In all locations, death of the larva provokes a more intense inflammatory response, and in the case of an intraventricular lesion may lead to ependymitis. Parenchymal lesions consist of small cysts, large cysts and calcified lesions. Small (approximately 1.5 cm. in diameter) cysts may have a central area of relatively shorter T1 (isointense or hyperintense to cortex) and are uniformly hyperintense on T2-weighted images. Large (4-7 cm) cysts are usually multiloculated, adjacent to the subarachnoid space and may contain a mural nodule. The presence of a mural nodule or a T2-hypointense rim in encapsulated lesions may correlate with larval death. Visualization of calcified lesions has been variable with MR; overall there is an advantage for CT in this regard. Sometimes, calcified lesions are surrounded by edema, making them more conspicuous on MR. Basal cistern lesions can be difficult to identify but have been visualized as areas of intermediate signal intensity on T1-weighted images. Intraventricular cysticercosis results in deformable and mobile cysts that may cause intermittent hydrocephalus.

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