Comparative study of CT and MRI in patients with seizures and a solitary cerebral cysticercus granuloma.

We hypothesized that when contrast-enhanced CT reveals a solitary cerebral cysticercus granuloma, MRI would not usually provide additional information that might assist in management. We retrospectively compared visualisation of solitary cysticercus granulomas on contrast-enhanced CT and MRI in 16 patients presenting with seizures; gadolinium (Gd) enhancement was used in 6 patients. The granuloma was delineated well on both CT and MRI in 15 patients; in one patient, in whom CT was performed with 10-mm slices, it was seen only on contrast-enhanced MRI, CT and unenhanced MRI revealing only the surrounding oedema. On CT the granuloma was seen best on thin (2-5 mm) contrast-enhanced sections (in 10 patients). On MRI, Gd-enhanced images showed the granuloma best, as a ring-enhancing lesion, in all 6 patients. In the other 10 patients, the granuloma was seen only on T2-weighted images in 8 and on both T1- and T2-weighted images in 2. On T2-weighted images a characteristic low-signal ring with a high-signal centre was seen in 12 patients. Sensitivity of the imaging techniques was: contrast-enhanced CT (5 and 10 mm slices) 93.8% (15/16); thin (2-5 mm) section contrast-enhanced CT 100% (6/6); unenhanced MRI 93.8% (15/16). MRI did not reveal additional granulomas or cysts in any patient. In patients strongly suspected to be harbouring this lesion, when 10-mm contrast-enhanced CT reveals only oedema, thin (2-5 mm) slice CT is a cost-effective alternative to MRI.