The limitation of computerized tomographic diagnosis of intracranial midline cysts.

The diagnosis of intracranial cystic lesions is greatly facilitated by cranial computerized tomography (CT) which eliminates the need for further invasive neuroradiological studies. However, cystic lesions with thin walls that do not enhance following intravenous contrast infusion, especially when they are located in the midline and at the base of the skull, may become a diagnostic problem preventing proper management and therapy. We discuss 12 midline intracranial lesions, including one that is noncystic, to emphasize the limitations of CT in showing these lesions and the need for further diagnostic studies such as pneumoencephalography and metrizamide CT. The limitations of CT in diagnosing these lesions are related to the variations in the anatomy at the base of the skull (supra-sellar region); the varying pathological nature and behavior of certain cystic lesions such as epidermoid tumors and craniopharyngiomas; and the compromising of the spatial and density resolutions due to the partial volume effect. The complementary role of studies such as pneumoencephalography and CT metrizamide cisternography for the evaluation of the dynamics of the cerebrospinal fluid that are necessary for the proper management and therapy of patients is discussed.