Of the Vascular Anatomy of Nerves

Our knowledge of the anatomy of the blood supply of nerves has long withstood a dignified antiquity. Even before the publication of Harvey's classic paper on the circulation of the blood the Belgian anatomist, van der Spieghel (1627), wrote of the vasa nervorum in man, ' It is ridiculous to think, as Aristotle stated in his account of the body, that there should be any mucous-like, whitish and glutinous substance around the nerves, from which the nerves themselves spring and from which they are nourished, when their nourishment may be obtained from these vessels.' Ruysch (1701), von Haller (1752) and Schmidel (I755) were all well aware of the presence of blood vessels to nerves and of their potential significance, and Boerhaave (1762) considered that knowledge of the blood supply of nerves would pave the way for the understanding of many of their diseases, ' so that it by no means is to be placed amongst the anatomical minutiae to be excluded altogether from the attention of the practitioner.' In I768 Isenflamm and Doerffler published what appears to have been the first work devoted exclusively to the blood supply of nerves, a paper entitled De Vasis Nervorum. They had demonstrated fine vascular branches in the sheaths of peripheral nerves, of which they observed ' filling the latter (vessels) with coloured wax makes them elegantly conspicuous and gives a likeness of a painted vascular net enveloping the nerve.' They were also familiar with the intrinsic vascular plexuses which ramify in the endoneurial and perineurial sheaths of peripheral nerve trunks, and which were described in more detail by Ranvier (I878). He established that they were for the most part composed of longitudinally disposed vessels between which there were frequent transverse anastomoses; the plexuses were both intrafascicular and perifascicular in distribution. Quenu and Lejars (I890, 1892 and I894) paid particular attention to the numerous anastomoses between adjacent vasa nervorum, both on the surfaces of nerve trunks in the epineurium, and in their substance; they considered that the presence of these anastomoses would render a total interruption of the blood supply extremely unlikely. The intercommunications of the veins draining nerve trunks were considered even more conspicuous than were those of the arteries of supply, and particular significance was attached to the fact that they tended to open into venous tributaries from muscles, as venous return would thus be accelerated by muscular contraction. After the end of the i9th century anatomical investigations into the blood supply of nerves were limited to the detailed vascular topography of a number of different nerve trunks and to the elaboration of points of detail, but no new basic principles emerged to add to those previously established. The inferences regarding the relative importance of the regional nutrient vessels and of the intrinsic longitudinal vascular plexuses of nerve trunks which may be drawn from data on their vascular anatomy must, of necessity, be very limited, for the effectiveness of intercommunications between adjacent groups of vasa nervorum cannot be judged on anatomical grounds alone. The evidence relating to the problem of whether or not the blood supply of nerves is functionally segmental has come from other sources, partly from direct and indirect experimental approaches and partly from investigations into the influence of regional blood supply on the degeneration and regeneration of nerve fibres. The main findings from each of these sources are here considered in turn and the present status of the vasa nervorum and the clinical implications of their anatomy are discussed.