Lymph Vessels of the Mediastinum

The lymph vessels of the mediastinum (Figure 17: 4, 5, 6, 6¹, 6²) drain to the cranial mediastinal lymph nodes, the sternal lymph node, the middle tracheobronchial lymph node, the cranial lumbar aortic lymph node, the gastric lymph node, the splenic lymph nodes, and the left hepatic lymph node. Extensive, fine lymph vessel networks fill up at the puncture injection site.

The lymph vessel networks can be filled in the same way as those of the costal and diaphragmatic pleura; both by puncture injection and by introducing the injection fluid into the pleural cavity and mimicking respiratory movements.

a. The lymph vessels of the precardial mediastinum

The lymph vessels of the precardial mediastinum (Figure 17: 4) drain to the cranial mediastinal lymph nodes (Figure 17: a, a¹) and the sternal lymph node (Figure 17: c), as shown in Figure 17. The lymph vessels draining into the cranial mediastinal lymph nodes usually accompany the largest of the Aa.  (Vv.) mediastinales craniales.

b. The lymph vessels from the cardiac part of the mediastinum

The lymph vessels from the cardiac part of the mediastinum (Figure 17: 5) cannot be clearly separated from those of the pericardium.

i. Ventral Half of the Pericardium

Some of the lymph vessels from the ventral half of both the pericardium and the cardiac mediastinum run ventrally towards the sternum, then turn towards the thoracic inlet, accompany the internal mammary artery and vein, and drain to the sternal lymph node (Figure 17: c) while some of these lymph vessels preferentially run with larger cranial mediastinal arteries and veins, and join the lymph vessels of the precardiac mediastinum to drain to the cranial mediastinal lymph nodes (Figure 17: a¹, a²). A second group of lymph vessels run dorsally and reach the phrenic nerve, or its vicinity, running with the nerve cranially and draining to the cranial mediastinal lymph nodes (Figure 17: a¹). From many puncture injection sites, the lymph vessels filled in both dorsal and ventral directions.

ii. Dorsal Half of the Pericardium

Most of the lymph vessels from the dorsal half of the pericardium and the cardiac mediastinum join the second group of lymph vessels mentioned above, though some may additionally join the lymph vessels of the postcardiac mediastinum, which pass through the diaphragm, to drain to either the cranial lumbar aortic lymph node or to the gastric, splenic, or left hepatic lymph nodes (see below). Two to 3 lymph vessels arise from the caudodorsal part of the left pericardial wall and ascend directly in the mediastinum to the middle tracheobronchial lymph node (Figure 17: b’).

c. The lymph vessels from the postcardial part of the mediastinum

The lymph vessels from the postcardial part of the mediastinum (Figure 17: 6, 6¹, 6²) drain to the sternal lymph node, the middle tracheobronchial lymph node, and the cranial lumbar aortic lymph node. Some of the lymph vessels from the dorsal part of the postcardial mediastinum, the part extending caudally from the aortic arch, between the thoracic aorta and the esophagus (Figure 17: 6²), run cranially to the middle tracheobronchial lymph node (Figure 17: b¹), while others run caudally. Of the lymph vessels running caudally, some join the lymph vessels of the pars lumbalis of the diaphragm (see lymph vessels of the diaphragm) and pass with them, through the aortic hiatus, into the abdominal cavity to drain to the cranial lumbar aortic lymph node (Figure 17: d), while others (Figure 17: f) join the lymph vessels of the esophagus and enter with them, through the esophageal hiatus, into the abdominal cavity (Figure 28: 7, 7’) to drain to the gastric, splenic, or left hepatic lymph nodes (Figure 28: 1, 8).

Most of the lymph vessels from the part of the mediastinum situated directly ventral to the esophagus, between the esophagus and the left phrenic nerve (Figure 17: 6¹), drain to the middle tracheobronchial lymph node (Figure 17: b¹). These lymph vessels usually turn towards the truncus oesophageus ventralis of the vagus nerves and accompany it to the middle tracheobronchial lymph node, merging into 2 to 3 vessels. A small number of these lymph vessels also join the lymph vessels that penetrate the diaphragm (Figure 17: e), which are described below.

Lymph vessels from the ventral part of the postcardial mediastinum (the part ventral to the left phrenic nerve) merge to form 3 to 4 vessels, 1 to 2 of which enter the diaphragm near the phrenic nerve, penetrating it at or near the central tendon (Figure 17: e), and passing under the peritoneum to the esophageal hiatus. From there, the lymph vessels will either drain into the cranial lumbar aortic lymph node or into the gastric, left hepatic, or splenic lymph nodes. Additionally, 1 of these lymph vessels may also join the lymph vessels draining into the middle tracheobronchial lymph node (Figure 17: b¹). The other 1 to 2 lymph vessels from the ventral part of the postcardial mediastinum either run ventrally or run directly to the diaphragm, travel under the M. transversus thoracis with the lymph vessels of the diaphragm, and drain to the sternal lymph node (Figure 17: c).

The lymph vessels of the plica vena cava show the same behaviour as the lymph vessels of the ventral part of the postcardial mediastinum.