The hepatic veins in health and disease

Abstract

"La phlébite domine toute la pathologie" wrote Cruveilhier in his great work on morbid anatomy more than a hundred years ago. Since then venous disease has become of less account. No modern writer could make Cruveilhierts claim, and diseases of veins now receive less attention than they deserve. In many parts of the body compensation for temporary or permanent venous occlusions is readily achieved and functional perfection of the venous system masks the presence of extensive lesions. But this is not the case in the liver. Such channels as exist collateral to the hepatic veins are totally inadequate for the great flow of blood through the liver, and the organ is more affected than most other viscera by venous occlusions.Where hepatic- venous occlusions are extensive compensatory readjustments of circulation may suffice for a while to obscure the severe congestion of the liver, but the clinical manifestations are eventually striking. This occurs in the Budd- Chiari! Syndrome, and a chapter of this thesis is devoted to cases of that condition in which the occlusions were not secondary to disease of other organs. In another chapter experimentally induced venous congestion of the liver of the rat is described. Although the Budd -Chiari Syndrome is rare, these instances of severe venous congestion are of general interest in relation to other and commoner hepatic conditions. Passive venous congestion of the liver is a frequent sequel to heart failure. The simplicity of pathogenesis in the conditions studied here however, and, in many instances, the slow tempo of their advance make them useful standards of comparison in any investigation of the more complex pathogenesis of portal cirrhosis and of the phenomena of ascites. Further, the recent descriptions of "Veno- occlusive disease" in Jamaica and possibly elsewhere makes it desirable to reassess the causes and effects of occlusions of the hepatic veins as they are encountered in this country.To understand the causes of hepatic -venous occlusions and their effects on the liver it is necessary to consider some of the less known facts and some debatable theories concerning the normal structure and the function of the hepatic - venous system in health and these form the subject in the earlier chapters of the thesis. The afferent portions of the hepatic circulation have been studied widely in the past few decades in connection with diseases of the liver, but the efferent portions have been relatively neglected. Accordingly some of the scattered information on the structure of the hepatic veins of man has been reviewed and checked by personal observations. Similar studies on animals are of almost equal importance because structural 'differences exist between species which render it impossible to :extrapolate unreservedly to human problems the results of observations on the hepatic circulation in animals. While observations on structure cannot be translated directly into functional terms, function can be understood only in the context f structure, whether that be gross, microscopical or ultra - ,microscopical. Where direct measurements of flow, pressure and other elements are few or unreliable, as in the case of the iv hepatic veins and their small radicles, useful deductions regarding the action of the vessels and the flow through them can still be drawn from a sufficiently comprehensive examination of their structure.