Posterior fossa lesions: magnetic resonance imaging.

Studies of 40 patients with abnormalities of the posterior fossa shown on magnetic resonance (MR) imaging were reviewed and compared with CT scans. Thirteen lesions were demonstrated on MR only. Twenty-four lesions were shown on CT but MR provided more data. Three lesions were better shown on CT than on MR. MR is superior to CT because of the lack of streak artifacts and better contrast discrimination. At least two imaging sequences are required for evaluation of the lesions.