Radiology--including computed tomography--of parasitic diseases of the central nervous system.

Neurocysticercosis is the commonest parasitic infection seen in India. Echinococcus is rare. In cysticercosis multiple diffuse cystic parenchymal lesions predominate in the East, whereas multiple diffuse basal racemose ones predominate in the West. Because of their protean and varied clinical picture, each patient in the past had at least two contrast studies and some even three such studies, before the availability of the CT scan. Angiographic evidence of arteritis and infarcts is documented in the Mexican studies and not seen in the Indian studies. Air studies reveal atrophy of brain parenchyma with demonstration of large cysts, intraventricular or basal. Small diffuse cysts are rarely demonstrated on these studies. CT has proved to be a boon in separating the various pathological groups. The diffuse parenchymal group shows an image morphology of throttled ventricles with or without high attenuating sago grain lesions. This is pathognomonic in endemic areas. The CT image of the localized parenchymal lesions is non-specific and can be mistaken for granulomas, abscesses or tumour. The intraventricular group and basal racemose forms give rise to oozing ventricles with obstructive of communicating hydrocephalus and disproportionate enlargement of the aqueduct and fourth ventricle in the acute stage. The cyst itself is not seen separate from the CSF in the ventricles. The disease runs a prolonged course of relapses and remissions leading to parenchymal atrophy and calcification of the intracranial and soft tissue cysts. The incidence and morphology of calcification varies in different parts of the world from 2.8% in India to 39% in Mexico and 71% in Los Angeles.(ABSTRACT TRUNCATED AT 250 WORDS)