Radical excision is the surgical goal whenever possible, but must minimize damage to the normal parenchyma and function of the brain. Hypotension, temporary occlusion of involved vessels (Gillingham 1953), identification of afferent and efferent vessels with fluorescein angiography (Feindel et al. 1965), intracranial, intraoperative flow measurement (Nornes and Grip 1980), multiple stage operations (Pertuiset and Sichez 1978) and interdisciplinary attack (embolization by neuroradiologist and removal by neurosurgeon, Stein and Wolpert 1980) are recently available useful technical adjuncts. Stereotactic approaches (Guiot et al. 1960, Riechert and Mundinger 1964, Wijnalda and Bosch 1975, Kandel and Peresedov 1977), electrothrombosis (Handa et al. 1977), and cryosurgery (Walder et al. 1970) have not found widespread acceptance. Techniques of hypothermia, circulatory arrest and circulatory bypass and the use of steroids (Edgerton 1983, Nagamine et al. 1983) have all been employed with some success. Yet other techniques such as gamma radiation (Steiner et al. 1972), proton beam therapy (Kjellberg 1978) and selective embolization (Brooks 1930, Luessenhop and Spence 1960, Sano et al. 1965, Djindjian 1970, Doppman et al. 1971, Serbinenko 1974, Hilal et al. 1974, Wolpert and Stein 1975, Debrun et al. 1975, Russell and Berenstein 1981, Merland et al. 1983, and others) have great potential.
If the associated disadvantages of these techniques can be overcome it would be a great dream to eliminate the kidnapper of the normal cerebral circulation in a non-surgical way. It seems probable for the present, that we shall need to develop even more effective surgical techniques to provide results which can then be compared with those of modern radiation. This will only be possible by the application of perfect microsurgery, which necessitates training in the laboratory to gain competence in manipulating brain vessels, in taming and controlling abnormal vessels and thus in effecting complete removal of the malformation.
1 Diagnosis made at exploration
2 Diagnosis made clinically rest: Diagnosis made at autopsy
2 Embryology
Miguel Marin-Padilla
A. Embryogenesis of the Early Vascularization of the Central Nervous System
Introduction
The vascularization of the central nervous system (CNS) is a complex process, best described as an integrative vascular metamorphosis continuously adapting to its developmental modifications. Embryonic development of the CNS itself is also complex. It consists of the progressive transformation of a tubular structure (neural tube) into several regions, each with a different and specific structural organization. The vascularization of each of these regions is an integrated process which adapts to its particular growing structural and functional needs. While these regional vascular differences are clinically and surgically relevant, there are common features in the early vascularization of the CNS shared by all its regions. In the present chapter, common developmental features that characterize the general vascularization of the CNS, rather than regional differences, will be emphasized.
The available information concerning anatomic, histologic, pathologic, radiographic, clinical and surgical aspects of the formed CNS vasculature is enormous and can be readily obtained from a variety of books, monographs and review articles (Kaplan and Ford 1966, Taveras and Wood 1964, Van den Bergh 1967, Van den Bergh and Vander Eecken 1968, Stephens and Stilwell 1969, Kety 1972, Newton and Potts 1974, Peters et al. 1976, Kautzky et al. 1982, Dudley 1982, McCormick 1983, Yaşargil 1984). Although, information is also available concerning the embryonic development of the CNS vasculature (Mall 1904, Streeter 1918, Padget 1948, 1957, Moffat 1962, Klosovskii 1963, Pessacq and Reissenweber 1972, Hamilton et al. 1972, Bär and Wolff 1972, Gamble 1975, Hauw et al. 1975, Wolff et al. 1975, Pape and Wigglesworth 1979) some early aspects of it remain poorly understood.
The actual perforation of the CNS surface by embryonic vessels as well as the sequential establishment of its vascular territories needs further investigation. Information is also needed concerning the interrelationships between the development of the CNS vascular territories and that of the meningeal, the Virchow-Robin and the intraneural glial tissue compartments.
Early in embryonic development the neural tube, as a specialized epithelial (neuroectoderm) tissue, lacks an inherent vasculature (Sabin 1917, Streeter 1918, Strong 1961, Hamilton et al. 1972, Marin-Padilla 1985b). Therefore, it should be possible to study the early embryonic vascularization of any of its regions. The vascularization of the neural tube follows a caudal-cephalad gradient which is synchronous with that of its ascending differentiation and maturation. In any given region of the developing CNS, embryonic vessels must first surround and organize around (outside of) it; secondly, they must perforate the CNS external basal lamina and marginal glia, which constitute an anatomic barrier; and, thirdly, they must grow within the developing neural tissue while adapting to its growing structural and functional needs. Thus, three different vascular territories must progressively emerge in the early vascularization of every region of the developing CNS. They are the perineural, the interneural and the intraneural vascular territories, respectively. The term “neural” used to describe these three vascular territories encompasses “nervous (neural) tissue”. In other words, vascular territories which embryologically evolve outside (peri), in between (inter) and inside (intra) nervous tissue, respectively.
Each vascular territory, though interrelated, evolves sequentially, independently, and within a different and specific tissue compartment. Each territory gives rise to different types of vessels. The main arterial and venous systems of the CNS, which are components of the perineural vascular territory, evolve embedded within the meningeal compartments. Most of the perforating arterioles and venules of the CNS vasculature, which are components of the interneural vascular territory, evolve within the Virchow-Robin compartment (VRC) and hence are outside, “in between” the nervous tissue proper. Thus, the term interneural is introduced to characterize this territory of the CNS vasculature. Finally, the capillaries, apparently the only vessels that penetrate the nervous tissue proper, constitute the intraneural territory of the CNS vasculature. Intraneural capillaries also evolve embedded within a specialized compartment represented by the perivascular glia.
The early embryonic development and sequential establishment of each of these three vascular territories will be analyzed in association with the development of the meningeal, the Virchow-Robin, and the intraneural perivascular glia compartments, respectively.
Since a study of the early vasculogenesis of every region of the CNS would be too complex and beyond the scope of this text, only that of the embryonic cerebral cortex will be considered in detail (see also: Marin-Padilla 1970, 1971, 1978, 1982, 1983). Nevertheless, it should be emphasized that the observations presented and discussed should be fundamentally applicable to the early vascularization of all regions of the CNS.
Perineural Vascular Territory of the CNS Vasculature
Vasculogenesis starts in situ from consolidated angioblastic cell islands found throughout the mesoderm, the yolk sac and the body stalk of the young embryo. The cellular elements of these islands seem to undergo progressive cytoplasmic liquefaction (Sabin 1917, 1920) which results in their eventual canalization. However, the process of canalization of these islands as well as that of growing capillaries remains poorly understood and controversial (Manasek 1971). Progressive canalization of the angioblastic islands results in the formation of a precirculatory plexus of primordial vessels which are large, irregular and composed of several endothelial cells joined by tight junctions. They are surrounded by a thin and often incomplete basal lamina, and grow actively by sprouting. Zones of vascular growth are deprived of basal lamina and their leading endothelial cell or cells produce numerous long filopodia able to advance into the surrounding tissue (see Figs 2.11, 2.12). Blood cells are also believed to evolve from the original angioblasts (Streeter 1918, Sabin 1920) and they are identified
