[Incisural block. Radiological diagnosis].

Radioisotope cisternography is the best method for studying the third circulation. A new mode of representation is proposed for understanding the importance of the various foramina and the main direction of the bulk flow. The incisura tentorii plays an important role in the cranial leptomeningeal space. Particular emphasis is given to the cisternographic and pneumographic patterns of its stenosis and occlusion. Incisural block may be anatomical (primary) or functional (secondary). That distinction gives the choice between different shunting procedures. Its significance is demonstrated and illustrated in various situations.