Blood supply of the caudal mediastinal lymph node in sheep

We investigated the arterial supply to, and the venous drainage from, the caudal mediastinal lymph node (CMN) in 18 anesthetized and exsanguinated sheep. The purpose of this gross anatomic investigation was to determine the CMN's blood supply so that a structural base can be used to interpret studies of the bronchial circulation's role in the pathogenesis of pulmonary edema. In ten sheep, we cannulated the bronchoesophageal artery at its origin from the aorta and injected Microfil. This artery, which branches into cranial and caudal divisions 2-4 mm distal to its origin, supplied the esophagus, trachea, bronchi, and visceral pleura. The CMN is supplied by the caudal division, as it courses between the CMN and aorta. Microfil injected through the thoracic aorta did not enter the CMN when the bronchoesophageal artery was ligated at its origin. These results indicate that only the bronchoesophageal artery supplies the CMN. In eight sheep we cannulated the vein at the head of the CMN (dorsal mediastinal vein) and injected Microfil, both peripherally and centrally. Peripherally, injected veins reached the CMN and esophagus. The dorsal mediastinal vein extended posteriorly to the CMN in three of the eight sheep, eventually emptying into the left azygos vein near the diaphragm. Centrally, the dorsal mediastinal vein joined the left azygos vein near the heart in six of the eight sheep, including the three in which the dorsal mediastinal vein extended posteriorly to the CMN. In the remaining two sheep the dorsal mediastinal vein drained centrally into the right azygos vein. We conclude that the bronchoesophageal artery supplies the CMN and that either the left or right azygos vein drains it.