Lymph Vessels of the Kidneys
The lymph vessels of the kidneys (Figure 27: f, f’) are divided into two groups: those of the renal capsule and those of the renal parenchyma.
A. Lymph Vessels of the Renal Capsule
The lymph vessels of the renal capsule form extensive networks within the capsule. The lymph vessels arising from the capsular networks drain to the lumbar aortic lymph nodes, including the cranial lumbar aortic lymph node, and can drain to all lymph nodes in this group, even the most caudal ones. The lymph vessels from the cranial part of the renal capsule usually drain to the cranial lumbar aortic lymph node (Figure 27: 1, 1’) and to the lumbar aortic lymph node located at the renal artery and vein (Figure 27: 2). The lymph vessels from the caudal part of the renal capsule usually drain to the lumbar aortic lymph node located at the renal artery and vein, as well as the lumbar aortic lymph nodes caudal to it (Figure 27: 3). The lymph vessels emerge from all parts of the capsule, first running between the fibrous renal capsule and either the adipose capsule or serosa (the peritoneum) to the medial, cranial, or caudal margin of the kidney, and, from there, run subperitoneally to the lymph nodes mentioned above. Frequently, individual lymph vessels form large arcs that extend in a caudal direction.
A connection between the capsular and the parenchymal lymph vessels could be established. When puncturing and injecting the parenchyma, particularly its superficial layer, capsular lymph vessels were almost always filled. But it is difficult to determine whether capsular lymph vessels enter the parenchyma and join or merge with its lymph vessels. In several cases, I was able to demonstrate that the injected capsular lymph vessels did not run into the kidney but instead went directly to the lymph nodes. In other cases, in addition to the lymph vessels draining directly to the lymph nodes, parenchymal lymph vessels were also filled. However, it was never clear in such cases whether this filling was truly from the capsule or, more specifically, from the capsular lymph vessels. Due to the thinness of the fibrous capsule, it was rare to fill only capsular lymph vessels – the capsule itself will always be punctured, and the lymph vessels of the renal surface will be filled. This can then be mistaken for capsular lymph vessels connecting to the parenchymal lymph vessels.
I was also able to demonstrate that lymph vessels in the fibrous capsule were present in all cases. Therefore, I could not confirm the statement by Kumita [22] that the fibrous capsule of the kidney lacks lymph vessels in some cases, and that capsular lymph vessels penetrate the parenchyma. I will address these areas in a detailed paper. The lymph vessels of the adipose capsule join those of the fibrous capsule.
B. Lymph Vessels of the Renal Parenchyma
The lymph vessels of the renal parenchyma leave the kidney through its hilus in the form of 5 to 8 lymph vessels of varying sizes, which travel with the renal blood vessels to drain to the closest lumbar aortic lymph nodes. Lymph vessels from these lymph nodes then usually run to the more caudally located lumbar aortic lymph nodes and then to the medial iliac lymph node, and also in the cranial direction to the cranial lumbar aortic lymph node. Parenchymal lymph vessels may also drain directly to the cranial lumbar aortic lymph node. Additionally, since the lymph vessels of the capsule almost always fill during the injection of dye into the parenchymal lymphatics (see above), and the capsular lymph vessels drain to the cranial lumbar aortic lymph node and the more caudally located lumbar aortic lymph nodes, these lymph nodes will also fill with dye during injection of parenchymal lymph vessels.
Lymph vessels of the kidney and the renal capsule could not be traced directly to the medial iliac lymph node, but relatively often (6 times in 12 examined dogs, or in half of all cases), I observed that the lymph vessels of both the kidney and the renal capsule opened directly into the cisterna chyli (for details see Baum [8]). Additionally, the lymph vessels of the renal capsule are often connected with the testicular lymph vessels (see lymph vessels of the testis).
