Lymph Vessels of the Liver and Gallbladder
The lymph vessels of the liver can also be divided into superficial (subserosal) and deep (parenchymal) vessels. The superficial lymph vessels fill up particularly during puncture injections into the serosa and the most superficial parenchymal layers. These lymph vessels form fine serous or subserosal networks, as shown in several places in Figure 28. Most of the lymph vessels arising from these networks continue only a short distance subserosally or in the serosa (Figure 28: 4, 4, 4), before travelling more deeply and joining the deep lymph vessels. They often travel more deeply immediately (especially on the parietal or diaphragmatic surface of the liver), though a smaller number of subserosal lymph vessels can be followed over long distances, even up to the hepatic portal or to the point where the lymph vessels leave the liver, for example, to the coronary ligament or the lateral ligament (Figure 28: 5, 5, 9, 9’). Less commonly, superficial lymph vessels fill after injections into the liver parenchyma, i.e. lymph vessels that emerge from the depth to the surface. Deep lymph vessels, of course, fill primarily when injections are made into the liver parenchyma, but may also fill when, as has been described above, superficial lymph vessels penetrate more deeply.
The lymph vessels of the liver, both superficial and deep, drain to the left hepatic lymph node, the right hepatic lymph nodes, the gastric lymph node, and the splenic lymph nodes. The superficial lymph vessels additionally drain to the cranial lumbar aortic lymph node.
A. The Diaphragmatic Surface of the Liver
The superficial (subserosal) lymph vessels of the parietal or diaphragmatic surface of the liver can be divided into 3 groups based on their behaviour: some of the lymph vessels run deeply and join the deep lymph vessels of the liver, some enter the lateral ligament and coronary ligament of the liver and run from there towards the diaphragm, and, finally, some can be followed subserosally to the hepatic lymph nodes.
The first group includes subserosal lymph vessels from the entire parietal surface, but particularly from its ventral half.
The second group includes subserosal lymph vessels that originate from the dorsal half of the parietal surface, particularly from the part of the parietal surface that is adjacent to the dorsal part of the lateral margins of the liver. These lymph vessels approach the diaphragm as described above, but then, as was found in 8 closely examined cases, do not enter the thoracic cavity, instead running along the diaphragm under its peritoneum. Some drain to the cranial lumbar aortic lymph node (right and left) (Figure 28: 9, 9’, 3, 3’), and some run towards the vena cava and the end of the esophagus, at this point joining the parenchymal lymph vessels emerging from a depth (see below), and then, together with the lymph vessels of the esophagus (Figure 28: n), drain to the splenic, gastric, and left hepatic lymph nodes (Figure 28: 7, 7’, 1, 8). Some of these lymph vessels run from the cardia, between serosa and muscularis of the stomach, to the small curvature and from here in the dorsal wall of the omentum and accompany the left gastric vein to the splenic vein, draining to the left hepatic lymph node (Figure 28: 1). If a gastric lymph node is present at the small curvature of the stomach, some of these lymph vessels enter it. The remaining lymph vessels run from the cardia, around its left side, to the gastrosplenic ligament and run within it to the splenic vein and to the splenic lymph nodes (Figure 28: 8).
Some of the lymph vessels mentioned above may additionally bend around the dorsal edge of the liver onto its visceral surface, where they join the deep lymph vessels emerging from the hepatic portal, draining with them into the hepatic lymph nodes. This third group of subserosal lymph vessels arises from the parietal surface of the liver, especially on the parietal surfaces of the individual lobes of the liver that are covered by adjacent lobes.
The superficial lymph vessels of the visceral surface are, for the most part, situated deeply (Figure 28: 4, 4, 4) and join with the deep hepatic lymph vessels. Some lymph vessels run subserosally to the hepatic lymph nodes (Figure 28: 5, 5, 1, 2), while others, especially those from the parts of the lateral hepatic lobes adjacent to the dorsal part of the lateral margins, enter the lateral ligaments of the liver and join the corresponding lymph vessels from the parietal surface to drain to the cranial lumbar aortic lymph nodes (see above and Figure 28: 10, 10’, 3, 3’). Finally, some lymph vessels from the dorsal part of the visceral surface join lymph vessels running to the vena cava and the end of the esophagus.
B. Deep Lymph Vessels of the Liver
The deep lymph vessels of the liver leave the liver in two places: 1) in the hepatic portal and 2) on the parietal surface of the liver, where the hepatic veins join with the vena cava.
i. Hepatic Portal
The deep lymph vessels (Figure 28: 6, 6) emerging in the hepatic portal arise from all the individual lobes, accompanied by the corresponding branch of the portal vein: several (4 to 12) lymph vessels arise from each lobe. Some of these lymph vessels merge in the hepatic portal and join the lymph vessels from the visceral surface of the liver (see above). Despite the union of the neighbouring lymph vessels, at least 50 to 70 lymph vessels can be counted in the hepatic portal as they exit the liver. These vessels are accompanied by the portal vein (Figure 28: e) and drain to all the lymph nodes in both the right hepatic lymph node group (Figure 28: 2) and the left hepatic lymph node group (Figure 28: 1), as shown in Figure 28. As they travel to these lymph nodes, the number of lymph vessels decreases, as they unite with neighbouring lymph vessels.
ii. Parietal Surface
The deep lymph vessels arising from the parietal (diaphragmatic) surface of the liver emerge in close proximity either to the hepatic veins or where these veins join the vena cava, and behave as described in more detail above; they mainly originate from the dorsal part of the liver adjacent to the vena cava.
The lymph vessels of the gallbladder (Figure 28: b) form extensive networks in the wall of the gallbladder. Two to 4 lymph vessels arise from these networks and accompany the common bile duct to drain into the right hepatic and left hepatic lymph nodes (Figure 28: 1, 2).
In humans, Franke [19] found that the lymph vessels of the gallbladder drained into a network of lymph vessels located on the dorsal aspect of the head of the pancreas – I have not observed the same or even similar findings in dogs. Additionally, the lymph vessels of the liver cannot be filled from the gallbladder, although, conversely, the lymph vessels of the parts of the liver adjacent to the gallbladder cross over to the gallbladder and merge with its lymph vessels.
