📝 STANDARD DESCRIPTION:
Main thoracic lymph nodes:
1. Cranial Mediastinal LN — at thoracic inlet, around great vessels.
2. Middle Mediastinal LN — between aortic arch & oesophagus.
3. Caudal Mediastinal LN — large, between oesophagus & aorta near diaphragm; drains diaphragm + lungs.
4. Tracheobronchial LN (Bronchial) — at bifurcation of trachea; Left, Right, Middle, Cranial nodes; drain LUNGS.
5. Intercostal LN — small, in dorsal intercostal spaces.
6. Sternal LN — on inside of sternum (cranial).
Thoracic Duct:
- Largest lymphatic vessel of the body.
- Begins at Cisterna Chyli (in abdomen, dorsal to aorta).
- Enters thorax through aortic hiatus.
- Runs on RIGHT side of aorta, then crosses to LEFT.
- Opens into cranial vena cava (or jugular vein) at thoracic inlet.
- Drains LYMPH from whole body except cranio-right quarter (which is drained by Right Lymphatic Duct).
📚 DETAILED DESCRIPTION:
LYMPH NODES & DUCT IN THE CHEST
Lymph nodes are small bean-shaped filters along lymph vessels. They trap microbes and tumour cells, and produce lymphocytes. In the thorax they are clinically very important because thoracic infections, TB, and tumours often show up here first.
MEDIASTINAL LYMPH NODES (around the mediastinum):
• Cranial mediastinal: At the thoracic inlet, around the cranial vena cava and aorta. Drain neck, cranial chest wall, and forelimbs.
• Middle mediastinal: Around the aortic arch and at the bifurcation of trachea.
• Caudal mediastinal: The largest in cattle — a long node lying between oesophagus and aorta near the diaphragm. Drains the diaphragm, oesophagus, and parts of the lungs.
BRONCHIAL (TRACHEOBRONCHIAL) LYMPH NODES:
Group of nodes around the bifurcation of the trachea. Named by position: cranial, middle, left, right tracheobronchial. They drain the LUNGS and are the first to be affected in bovine tuberculosis. Always examined in post-mortem inspection of cattle in slaughterhouses.
OTHER NODES:
• Intercostal LN — tiny, in some intercostal spaces near the heads of ribs; drain dorsal chest wall.
• Sternal LN — on inner side of sternum cranially; drain ventral chest wall, mammary gland (in some species).
THORACIC DUCT — the body's main lymph highway:
This is the LARGEST lymphatic vessel. It carries lymph (including absorbed dietary fat = chyle) from most of the body back into the venous bloodstream.
Course:
1. Begins in the abdomen as a sac-like swelling — the cisterna chyli — lying dorsal to the aorta.
2. Enters the chest through the aortic hiatus.
3. Runs forward along the right side of the aorta, gradually crossing to the left near the heart base.
4. At the thoracic inlet it bends downward and opens into the cranial vena cava (or sometimes the left external jugular near its junction with subclavian).
It drains lymph from: both hindlimbs, abdomen, pelvis, left forelimb, left side of head/neck, and most of the chest. Only the right forelimb + right side of head/neck + right side of chest are drained by the smaller right lymphatic duct.
// COMPARATIVE ANALYSIS
| HORSE |
Caudal mediastinal LN smaller; tracheobronchial nodes prominent. |
| DOG |
Mediastinal nodes can become hugely enlarged in lymphoma → 'cranial mediastinal mass syndrome'. |
| CATTLE |
Bronchial and mediastinal LNs are the standard sites for inspection in bovine TB. |
CLINICAL RELEVANCE
Bovine Tuberculosis: Bronchial and mediastinal lymph nodes show typical caseous (cheese-like) lesions. These nodes are routinely cut and inspected at meat inspection.
Chylothorax: Rupture of the thoracic duct → leakage of milky chyle into the chest cavity → severe breathing difficulty (more common in dogs and cats).
