Hepatic Lymph Nodes
The hepatic lymph nodes are located on the trunk of the portal vein and can be divided into two groups: the left hepatic lymph nodes (Figures 26: c; 28: 1) and the right hepatic lymph nodes (Figures 25: s; 26: b; and 28). The drainage areas of both the right and left lymph nodes are the liver, stomach, pancreas, and duodenum.
A. Left Hepatic Lymph Nodes
The left hepatic lymph node (Figures 26: c, 28: 1) is a somewhat elongated, usually slightly flattened lymph node, located to the left of and slightly dorsal to the trunk of the portal vein (Figure 26: 14), dorsal on the initial part of the duodenum (Figure 26: 2), and at the apex of the pancreatic loop (Figure 26: 3, 3’). The lymph node usually extends caudally to the gastrosplenic vein. In 5 of 25 cases, the caudal one-quarter of the lymph node extended beyond the gastrosplenic vein, and in 4 cases the lymph node bent at the gastrosplenic vein and extended along the vein’s cranial border towards the junction of the gastric vein and the splenic vein. In 4 cases, there was a 2nd, smaller lymph node, which, in 2 of the cases, lay on the caudal border of the gastrosplenic vein. In another case, there were 3 left hepatic lymph nodes. The left hepatic lymph node is the structure that is often termed the Pancreas of Aselli and is also named as such in the Anatomy of the Dog by Ellenberger and Baum. The size of the lymph nodes ranged from 1 to 6 cm, and the lymph nodes were at times so flattened that they appeared ribbon-shaped.
The left hepatic lymph node drains lymph vessels from the esophagus, stomach, liver and gall bladder, the pancreas, diaphragm, mediastinum and peritoneum, as well as the efferent lymph vessels of the gastric lymph node and the right hepatic lymph nodes.
The efferent lymph vessels emerging from the left hepatic lymph node merge to form 2 to 3 vessels, which join the efferent lymph vessels of the splenic lymph nodes (see splenic lymph nodes) to form the intestinal trunk, or the network of vessels acting as the intestinal trunk. There is retrograde flow to the splenic lymph nodes from the efferent vessels of the left hepatic lymph node. If there are several left hepatic lymph nodes, efferent vessels connect these lymph nodes, just as efferent vessels connect the left hepatic lymph node with the right hepatic lymph nodes (Figure 24: 1).
B. Right Hepatic Lymph Nodes
The right hepatic lymph nodes (Figures 25: 3; 26: b; and 28: 2) are a group of 1 to 5 lymph nodes of various sizes, located on the right side of the trunk of either the portal vein or the mesenteric vein. The number of right hepatic lymph nodes is highly variable. In 3 of 24 cases, there was only a single elongated, flat lymph node, which extended caudally from the gastroduodenal vein to the ileocolic vein and the right colic lymph node. In 9 cases, 2 lymph nodes, located one behind the other, were found at the described location. In the remaining cases, 3 to 5 lymph nodes were observed at the same location, almost always located one behind the other. In only 1 case, 2 of the lymph nodes were located one behind the other, while the 3rd lymph node extended across the dorsal aspect of the portal vein to the left hepatic lymph node. It is not uncommon for these lymph nodes to be so flat that they appear ribbon-shaped. Their sizes ranged between 1 and 5 cm.
The right hepatic lymph nodes drain the lymph vessels from the stomach, duodenum, pancreas, liver, and gall bladder, as well as the efferent lymph vessels of the duodenal lymph node, the omental lymph node, and the left hepatic lymph node.
The efferent vessels of the right hepatic lymph node(s) merge to form 4 to 8 larger vessels, which run over both of the surfaces of the portal vein towards the cranial mesenteric artery and contribute to the network of vessels acting as the intestinal trunk. If there are several lymph nodes present, they are also connected to one another in the same way that efferent vessels connect the right hepatic lymph nodes with the left hepatic lymph node (Figure 24: 2).