Posterior fossa extraaxial cyst: diagnosis with metrizamide CT cisternography.

This study describes a new technique for the study of posterior fossa extraaxial cysts. Using metrizamide (Amipaque) CT cisternography, a rapid, simple, low morbidity method is now available which gives both anatomic and physiologic information that may obviate the need for pneumoencephalography and angiography. Two cases are reported; in a third the diagnosis was definitively excluded. By doing serial CT scans following the intrathecal introduction of metrizamide, data concerning the diffusion characteristics of these cysts as well as the accompanying hydrocephalus are obtained.