Lymph Vessels of the Trachea
The tracheal lymph vessels (Figure 23: a, a) drain to the medial retropharyngeal lymph node (Figure 23: 1), the deep cervical lymph nodes (Figure 23: 2, 3, 4), the cranial mediastinal lymph nodes (Figure 23: 6, 6’), and the bronchial lymph nodes. A description of the drainage from the separate sections of the trachea follows:
a. Cervical trachea
The lymph vessels from the cranial third or fourth of the trachea (see Figure 23) drain to the medial retropharyngeal lymph node (Figure 23: 1). The small lymph vessels arising from both the lymphatic network of the mucous membrane and from the cartilage almost all emerge on the dorsal side, to a lesser extent on the lateral surface of the trachea, and continue on the trachea as 2 to 4 small vessels to drain to the medial retropharyngeal lymph node. If a cranial cervical lymph node (Figure 23: 2) is present, then some of the lymph vessels from the initial part of the trachea usually also drain to it (see Figure 23). However, I have also observed cases in which, despite the presence of a cranial cervical lymph node, no tracheal lymph vessels were observed entering it.
Small lymph vessels arise from the middle and caudal third of the cervical trachea, also emerging mainly on the dorsal, left, and right surfaces of the trachea and merging to form 1-2 larger vessels. These lymph vessels run caudally on the trachea (on the left side, also on the esophagus) and, when a caudal cervical lymph node (Figure 23: 4) is present, either some or all drain to this lymph node. A small number of the lymph vessels usually continue on to drain to a cranial mediastinal lymph node (Figure 23: 6, 6’): on the left side, usually into the cranial mediastinal lymph node located in the 1st intercostal space (Figure 23: 6) as well as the cranial mediastinal lymph node located on the left side of the cranial vena cava (Figure 23: 6’), and, on the right side, usually to the main cranial mediastinal lymph node (Figure 18: 3) that is located between the costocervical vein and the cranial vena cava. If the caudal cervical lymph node is absent, then all the lymph vessels drain directly into the cranial mediastinal lymph nodes. If (though rarely the case) a middle cervical lymph node (Figure 23: 3) is present, some of the lymph vessels of the cervical part of the trachea will additionally drain to it.
From the border area between the cranial and middle third of the cervical trachea, lymph vessels can drain in both directions; however, lymph vessels from the border between the cranial and middle third, and even those from the cranial quarter of the cervical trachea, may drain only to either the cranial mediastinal or caudal cervical lymph nodes. When lymph vessels are injected on one side of the trachea, they are frequently found to emerge on the other side of the trachea. It remains to be seen whether there is a true crossing of the median plane by the lymphatics, however, since there is always some degree of extravasation with the injection and this can reach the median plane.
b. Thoracic trachea (within the thoracic cavity) (Figure 18: r)
The lymph vessels from the cranial part of the thoracic trachea drain to the cranial mediastinal lymph nodes (Figure 18: 3, 31, 32, 33) and may enter any lymph node of this group. The lymph vessels from the caudal or terminal part of the trachea, as well as from the part of the main bronchi outside the lungs, drain to all the lymph nodes in the tracheobronchial lymph node group (Figure 18: 1, 2). Occasionally, a lymph vessel of the main bronchi may also drain to a pulmonary lymph node. The lymph vessels can emerge from all parts of the trachea between 2 tracheal rings.
Lymph vessels of the thoracic trachea were frequently observed to cross the median plane, so that, for example, the lymph vessels emerging on the left side of the trachea would drain to the cranial mediastinal lymph nodes located on the right side (contralateral drainage).
The lymph vessels of the tracheal mucosa form abundant networks of very tiny vessels. The lymph vessels emerging from these networks merge with the lymph vessels of the cartilage before they pass externally through the intercartilaginous spaces, so that lymph vessels of the mucosa and those of the cartilaginous rings cannot be clearly differentiated; the best differentiation is achieved when each group is injected separately. On the external aspect of the trachea, the lymph vessels form the usual large networks.
