Читать книгу Microneurosurgery, Volume IIIA - Mahmut Gazi Yasargil - Страница 9

Introduction

This volume attempts to provide the basis for an informed approach toward operating upon AVMs and for learning the actual operative techniques favoured by the authors. It is not meant to be a comprehensive review of all that has been written in the past upon the subject. While much of the material is based upon the findings and theories of others, some is also new. Historically, the development of new surgical disciplines has usually created a need for ever more detailed study of the embryology, anatomy, physiology and anesthesia relevant to that field. The particular needs of the surgeon have often stimulated new methods of carrying out these studies. Neurosurgery has been no exception. Initially, there was the need for a general understanding of the gross anatomy and the relationships and physiology of fiber tracts, cranial nerves and cortical structures, which would allow the surgeon to operate with relative safety within the limits imposed by the instrumentation, anesthesia, and illumination available at that particular time.

Cerebral angiography has been a real “breakthrough”, not only for diagnostic purposes but also for a better understanding of the hemodynamic and therefore the functional anatomy of the central nervous system. Neuroradiological anatomy, with entirely new perspectives was born and stimulated the neurosurgeon to expand his surgical activities. Refined angiography has permitted accurate study of vessels within the living brain, complementing the work of the pure anatomist. Selective and superselective angiographic techniques have been created as well as interventional neuroradiology. Endovascular neurosurgery was nothing more than the logical consequence of this accelerated development that has occurred within the last 20 years. Again the perspective concerning the anatomy of the central nervous system has been broadened.

The introduction of stereotactic techniques has led to the development of precise atlases of deep areas within the brain (Szikla et al. 1977) and now to computerized three dimensional maps of some of these structures (Salamon and Huang 1980, Unsöld et al. 1982).

At the same time, microtechniques were introduced into neurosurgery. The ability to reach areas, previously deemed inaccessible, with comparative safety, has dictated the need for a new perspective of the microanatomical and topographical relationship of almost every part of the cranial contents. The work of Basset (1952), Huang (1946–1985), Stephens and Stilwell (1969), Duvernoy (1969–1983), Waddington (1974), Newton and Potts (1974), Williams and Warwick (1975), Lang (1981), Seeger (1978,1980, 1984), has given us, in large part, the necessary topographical details. The elegant series of studies by Rhoton and his associates (1976–1985) describe precise microsurgical details of various brain areas, with their corresponding vasculature, from the point of view of the neurosurgeon. These neuroanatomical publications offer, besides profound and scientifically proven knowledge, very detailed geometrical, trigonometrical-arithmetical data concerning lengths and diameters of various bony, nervous and vascular structures, as well as distances between them. These painstaking and precise elaborations are essential background information, indispensable for every neurosurgical procedure. These major works, dealing with the brain stem vasculature comprise a precise review of the neurosurgical anatomy of the base of the brain, brain stem and circle of Willis. Our own account of the basal cisterns and circle of Willis has been described in Volume I.

Unlike the great majority of aneurysms, arteriovenous malformations and cerebral tumors are not confined to the basal regions of the brain. A new perspective must therefore be adopted, namely the awareness that even the deepest structures may often be reached by working carefully within the sulci and fissures of the brain. The basic patterns of these important anatomical structures should now be studied. Detailed accounts of sulcal and fissural anatomy are rare and generally incomplete but neurosurgery would certainly benefit from more precise studies in the future.

For this reason it seemed necessary to study, analyze and present the brain anatomy in a new concept, from the view point of the sulcal and fissural systems as well as their relation to the vessels.

Originally we planned to study the detailed anatomy of these systems in collaboration with Professor Kubik of Zurich, and to include these results in the present publication. This undertaking, however, turned out to be much more time-consuming than originally estimated.

The sulcal system showed an amazing degree of variation giving the impression of being a highly irregular system. As this study proceeded, however, it was realized that this irregularity of the sulcal system conforms to certain general principles. Despite the fascinating preliminary observations, we finally decided not to further delay the publication of this volume and to include here only the detailed anatomy of the calcarine sulcus and its variations and to present some representative displays of general sulcal anatomy. From this contribution by Professor Kubik, the reader will certainly become aware of the fascinating world of sulci. This interesting work will be continued and published later.

Although knowledge of sulcal and fissural anatomy is extremely important for angioma and tumor surgery, an equally detailed knowledge of microvascular anatomy is essential in order to perfect microsurgical techniques. Only with this knowledge can the neurosurgeon fulfil his goal, which is to preserve and protect the brain parenchyma adjacent to the lesion.

Since the pioneering work of Heubner (1872) and Duret (1873) on cerebral microvascularization and microcirculation, subsequent generations of anatomists further refined and extended their original concepts. Stimulated by the recent, excellent work of Duvernoy et al. of Besangon, France, we invited Professor Duvernoy to provide a concise chapter on cerebral microvascularization in order to stimulate younger colleagues to pursue the endeavours of modern anatomists.

We have been fortunate to have Professor Marin-Padilla of Hanover/New Hampshire, USA, who has contributed a concise chapter on the embryology of brain vessels, also summarizing the history in this field and adding his new ideas regarding the possible formation of cerebral vascular malformations. The development and maldevelopment of the cerebral venous system was intentionally not included in this volume, since this has been comprehensively described by Huang et al. as recently as 1984.

As we already noted in the first volume on aneurysms, the detailed anatomy of an AVM can only be completely and definitely evaluated at microsurgical exploration and not by any imaging technique. Although superselective angiography provides essential information regarding the composition of an AVM, we would like to have even more sophisticated angiographic techniques for even more precise study of the vascular composition and the hemodynamics of the AVM nidus and its compartments; this is already practiced daily by interventional neuroradiologists for vascular lesions of the skull base as well as head and neck. Professor Valavanis of Zurich, who performed all pre- and postoperative neuroradiological procedures since 1978, has been invited to provide the chapter on the neuroradiological evaluation of cerebral vascular malformations, also summarizing the relative role of CT, MRI and angiography. We refused to perform invasive studies to assess the hemodynamics of AVMs in our patients. However, we routinely applied non-invasive Doppler-ultrasound pre- and postoperatively. Professor Keller of Zurich, has contributed a separate chapter on his Doppler-ultrasound technique, summarizing the principles and the results of this method.

Modern neurosurgery is inherently dependant on the advances in neuroanesthetic techniques. During the last 20 years, five groups of anesthesiologists were involved in our daily work. The results achieved in the surgical management of intracranial AVMs were also possible thanks to the great effort of our neuroanesthesiologists, especially Drs. M. Curcic and Dr. M. Kis, who have been responsible for neuroanesthesia during the last 10 years.

In Volume III B of this series, the surgical techniques and results as well as the neuroanesthetic technique will be presented in detail.