General

The canine visceral lymph nodes are notably different from other animal species in that (1) they are sparse in comparison to other species (2) there are fewer groupings of lymph nodes than in most other species (e.g. humans, cattle). This is especially true for the stomach, liver, and pancreas.

At the most, the following lymph node groups can be categorized for the abdominal cavity viscera:

1. Hepatic lymph nodes (Lnn. portarum)^[1], which lie on the trunk of the portal vein and drain the liver, stomach, pancreas, and duodenum

2. Splenic lymph nodes (Lnn. lienales) on the splenic vein

3. Occasionally, a gastric lymph node (Ln. gastricus) on the stomach

4. Occasionally, an omental lymph node (Ln. omentalis) in the omentum

5. Almost always, a duodenal lymph node (Ln.  duodenalis) on the duodenum

6. Jejunal lymph nodes (Lnn. jejunales) on the jejunum and ileum

7. Colic lymph nodes (Lnn. colici) for the whole colon

The visceral lymph nodes are generally quite difficult to find because, due to their mostly light gray or less commonly brown color, they are barely demarcated from the surrounding mesenteric fat; this is especially true in cases in which the lymph nodes are so flattened that they appear almost ribbon-like (see hepatic lymph nodes). They can be found more easily by palpation of the entire mesentery and, above all, by injecting lymph vessels that drain to the lymph nodes. A total of 10 to 22 visceral lymph nodes were found in each of the 24 dogs examined. Most of the lymph nodes were of variable size, found individually or in groups, between the sheets of the intestinal mesentery and the omentum, and on the portal vein and its branches.

The sizes of the visceral lymph nodes are highly variable. With the exception of the lymph nodes located in the jejunal mesentery, which can be up to 20 cm long, 2 cm wide, and 1 cm thick, the visceral lymph nodes can reach a size of up to 6 cm in length, 1.5 cm in width, and 1 cm in thickness in large dogs, or be as small as a few millimeters. It is important to note that it is not uncommon for their shapes to be irregular, and so flattened that they appear to be ribbon-shaped. A ribbon shape was particularly common for the hepatic lymph nodes (see hepatic lymph nodes).