Occurrence and distribution of valves in the canine hepatic portal system

Major tributaries of the hepatic portal system were studied in 26 mongrel dogs to verify the occurrence and distribution of valves in this venous system. Methods included retrograde injection of modified Batson's no. 17 compound (16 splenic veins, 7 cranial mesenteric veins or its tributaries, and 6 caudal mesenteric veins), gross dissection (6 splenic veins and tributaries), and histologic sections (one specimen from each major drainage system). Functional valves, or cast impressions thereof, were common in each drainage system, and were present in veins ranging in diameter from 0.1 mm to 5.5 mm. Typically, valves were most abundant in veins directly draining an organ, such as segmental splenic veins and vasa recti of the small intestine. These valves were commonly located in close proximity to the confluence of two or more veins, or at the ostium of a comparatively small vein and a large vein. However, valves were also seen in the larger, more proximal veins of all three drainage systems, and these were not necessarily associated with the confluence of any major tributaries. This fundamental anatomic difference between dogs and humans should be noted by investigators using dogs as research models for portal system research.