[Cystic changes of the posterior cranial fossa on the nuclear magnetic resonance tomogram].

MR images were obtained in 15 patients with cystic lesions in the posterior fossa and the results compared with computed tomography (CT). The abnormalities imaged included 5 epidermoids, 3 haemangioblastomas, 4 arachnoid cysts, 1 postoperative cyst, and 4 large cisterns. One advantage of MR is the ability to demonstrate lesions in three planes and without artifacts. Liquor-related intensity measurements of cyst contents provided important information, thereby improving diagnostic specificity and patient management. T2-weighted images were found to be more sensitive in characterising cystic lesions of the posterior fossa than were T1-weighted images. Large cisterns, arachnoid and postoperative cysts had an intensity pattern identical or almost identical to cerebral spinal fluid. More proteinaceous cysts, including epidermoids and to a higher degree haemangioblastomas, had clearly higher intensity than cerebral spinal fluid on the T2-weighted images.