Mega cisterna magna: diagnosis using metrizamide computed tomographic cisternography.

The mega cisterna magna is one cause of a midline, extra-axial, posterior fossa cyst. The computed tomographic features and differential diagnosis of midline posterior fossa cystic structures are reviewed, and the clinical features of the mega cisterna magna are discussed. We describe a method of metrizamide cisternography and report a case of mega cisterna magna that was diagnosed by this technique.