[Abnormalities of the central nervous system in the area of the posterior cranial fossa--neuroradiologic and clinical aspects].

Since the introduction of CT, the assessment of ventricular enlargement and follow-up examinations after shunt surgery have become easier. By means of CT coronary and sagittal reconstructions as well as nuclearmagnetic resonance, the pathologic-anatomic changes in malformations with Arnold-Chiari II deformity and Dandy-Walker syndrome are clearly demonstrated. With nuclear magnetic resonance the morphology of structures in the posterior cranial fossa are demonstrated three-dimensionally, and in comparison with CT the method has the advantage that it involves no exposure to radiation. On the other hand, dynamic conditions of the CSF circulation can be evaluated better on the computerized tomogram following intrathecal injection of contrast medium. On the basis of our experience we believe that the different methods are complementary and can often be combined when planning surgery.