More than 800 papers were presented by neurosurgeons from 66 countries during the 7th International Congress of Neurological Surgery, held in Munich on 12-18 July 1981. With the present scope and problems of neurosurgery as its theme, the congress achieved its aims in making possible the exchange and dissemination of new knowledge and ideas and in facilitating personal contact between neurosurgeons from aU parts of the world. Of such importance are the regional differences within our branch of science that we should spare no effort in acquainting ourselves with those neurosurgical problems which lie beyond the boundaries of our local horizons. From the vast number of papers the editor has selected those whose high scientific standard merits greater exposure than that given by the conference itself. I should like to thank the editor for his work and Springer-Verlag for their involvement in our disci­ pline. It is to be hoped that this book will find a worldwide audience, in accordance with the intentions of the World Federation of Neurosurgical Societies. Prof. Dr. K.-A. Bushe President of the Congress v Editor's Preface This is the first volume of a new series which aims to provide an overview of the state of the art of neurosurgery every four years. It will contain papers covering various fields of our specialty, selected from among those presented at each International Congress of Neurological Surgery.