The lymphatic vessels of the lung: morphological study

Some variations in lymphatic drainage of selected bronchopulmonary segments in human lungs

Interest in the role of the pulmonary lymphatic system in the pathophysiology of pulmonary and systemic diseases induced us to carry out anatomical research on the lung lymphatic system in the Polish population. The aim of the study was to evaluate whether lymphatic vessels respect bronchopulmonary segment borders and to determine how often lymphatic vessels run to nodes of another lymphatic region. A block of organs comprising the lungs with the trachea, larynx and tongue, the heart and esophagus was removed from the cadavers at autopsy. The research involved 96 lungs (48 left and 48 right), which were taken from 31 male and 17 female cadavers. The lymphatic vessels were visualized at the mediastinal and interlobar surface of the lung by visual inspection. These vessels were then cannulated and injected with drawing ink. Next, the course of a lymphatic vessel was checked to see whether it was compatible with the bronchopulmonary segments or lobar borders. The first lymph node to become ink-colored via injection was dissected and histologically examined. A total of 135 images of lymphatic vessels (63 in the left lungs and 72 in the right lung) running on the mediastinal or interlobar surface of the lung were evaluated. In all, 12 out of 135 vessels (8.9%) were observed to cross the border of the segment (6/12 vessels) or the border of the lobe (6/12 vessels). We found 10/135 vessels (7.4%) running to the lymph nodes of another lymphatic region.

The problem of direct lymph drainage of the bronchopulmonary segments into the mediastinal and hilar lymph nodes

The phenomenon of skip metastases depends on the occurrence of direct metastases of non-small cell lung cancer into mediastinal lymph nodes without the involvement of hilar lymph nodes. The medical literature suggests that this prevalence ranges between 13 and 37.8% of cases. The goal of our study was to evaluate the prevalence of subpleural superficial lymphatic vessels carrying the lymph from the bronchopulmonary segments directly to the mediastinal nodes thus skipping the hilar nodes and determine whether there is a tendency towards differentiation in lymph drainage between males and females. During autopsy, 27 left and 27 right lungs were removed from 19 male and eight female cadavers. The lymphatic vessels were visualized at the mediastinal and interlobar surface of the lung by visual inspection. These vessels were then cannulated and injected with drawing ink. The first lymph node to become ink-colored via injection was dissected and histologically examined. The lymph flowed into hilar lymph nodes in 79.5% of the cases and into the mediastinal nodes in 20.5% of all the 83 vessels injected; of these 13.2% were from the right lung and in 7.2% from the left lung. The upper right lobe (5/14 vessels) and its anterior segment (3/14 vessels) were the most common source of the direct lymph drainage to the mediastinum. Vessels of 15.4% in female cadavers (4/26) and 22.8% vessels in male cadavers (13/57) traveled directly to mediastinal nodes skipping the hilar nodes. This difference was not statistically significant.

Pulmonary lymphatics and their spatial relationship to venous sphincters

BACKGROUND

Pulmonary lymphatics are critical to clearing lung fluid. Although their structure can be shown with light and transmission electron microscopy, scanning electron microscopy of their casts can better show their number, size, shape, distribution, and degree of filling. This technique has identified four forms of lung lymphatics, but these forms have not been fully evaluated by tissue microscopy. A most important site of pulmonary edema formation, the pulmonary capillary, is just upstream from small veins which have focal, smooth muscle tufts termed venous sphincters. Because of their constricting potential, these sphincters may control lung perfusion and cause edema.

METHODS

With light and transmission electron microscopy of tissue and scanning electron microscopy of casts, the lymphatic forms were explored in relation to the tissue anatomy in rats without pulmonary edema and with mild-to-moderate edema caused by extended vascular rinsing.

RESULTS

The edematous lungs had increased sacculo-tubular lymphatics adjacent to the venous sphincters. These lymphatics were in the adventitial connective tissue and were partially endothelialized. As lymphatics became more tubular their endothelium became more complete. Collagen fibers traversed the lumen of these lymphatics even where endothelial cells were present and caused the lines on the surface of the lymphatic casts. Overlapping endothelial cells caused clefts on the casts.

CONCLUSIONS

Scanning electron microscopy of lymphatic casts better defines their ultrastructure and shows the spatial relationship of veins and their sphincters to venous lymphatics. Sphincter contraction may influence pulmonary lymph production which could affect other aspects of regional lung perfusion.

Anatomic basis of lymphatic spread from carcinoma of the lung to the mediastinum: surgical and prognostic implications

Lymphatic spread of carcinoma of the lung to the mediastinum is an essential factor determining prognosis. An anatomic study of the mediastinal lymph nodes was made on 360 cadavers of adult subjects based on injection of the pulmonary segment. Eleven anatomic sites were involved. In 20 to 40% of cases the lymph reached these sites without any relay in the intrapulmonary lymph nodes. Within these sites the lymph flow continued towards the systemic circulation by traversing a variable number of lymph nodes, or sometimes none. The lymph flow reached the venous circulation in the neck, but in more than one case in ten the lymph had already entered the thoracic duct in the mediastinum, and in an intermediate number of cases the sites in the opposite mediastinum.

Forms of lung lymphatics: a scanning electron microscopic study of casts

In a recent study, rats given monocrotaline underwent angiogenesis on their pleural surfaces. The rats also had novel structures in their bronchovascular bundles that were detected by scanning electron microscopy of vascular casts. These vessels could have been either new blood capillaries or dilated lymphatic capillaries. To determine if these structures were lymphatics or new blood vessels, specimens from animals that were undergoing angiogenesis were compared to those that were not. Finding similar structures in normal animals would imply that they were lymphatic. The second purpose of this work was to describe the three-dimensional anatomy of the lymphatics of the lung. Cast lymphatics were found in most lungs with edema or angiogenesis, but were rare in other conditions. The vascular structures in question were found in animals not undergoing angiogenesis and were, therefore, lymphatic. Additionally, scanning electron microscopy of casts showed several distinct forms of lymphatics in the lung. Prelymphatics are tissues planes beneath the pleura and around bronchovascular structures. They join reservoir, conduit or tubulo-saccular lymphatics. Reservoir lymphatics are broad ribbon-like structures with textured surfaces and small laterally branching pouches. They occur on the pleural surface, are closely linked with prelymphatics, and join conduit lymphatics. Conduit lymphatics are tubular structures that may contain valves, twist and go great distances without accepting tributaries. On the pleural surface, they may wind around blood vessels and vary greatly in diameter. Sacculo-tubular lymphatics surround arteries, veins and bronchioles. They have thin walls with wide saccular segments. They may be so dense that they form cylinders around the vessels or airways. Different forms of lung lymphatics suggest different function and potential.

Inflammatory macrophages in the dog contain high amounts of intravesicular ferritin and are associated with pouches of connective tissue fibers

We have studied the subcellular distribution of ferritin in inflammatory macrophages present in regional lymph nodes from dogs subjected to a pulmonary inflammatory reaction. The inflammatory reaction was induced by intrabronchial instillation of calcium tungstate (CaWO4), a water-insoluble powder. Ferritin was identified by electron microscopy, and its electron density was enhanced by the use of a modified Perls method. From day 14 on after the CaWO4 deposition, tungsten-positive lymph node macrophages showed a massive accumulation of ferritin. Most of the ferritin was stored in membrane-bounded vesicles that showed heterogeneous concentrations of the protein. A significant complement of ferritin was also detected in the cytoplasmic ground substance of phagocytes. The cell surface of the ferritin-rich, tungsten-positive macrophages showed deep infoldings that encompassed small pockets of connective tissue fibers. These features were not observed in control samples or in lymph nodes from dogs subjected to CaWO4-induced inflammation for periods shorter than 1 week. Our data indicate that inflammatory macrophages greatly increase their content of ferritin macrophages greatly increased their content of ferritin and that ferritin is stored predominantly by a membrane-bounded vesicular compartment. This is in contrast with suggestions that the inflammation-induced increase in macrophage iron is restricted to the labile pool of iron and it does not involve the iron bound to ferritin molecules. Our observation of nodules of connective-tissue fibers in intimate topographical association with ferritin-rich macrophages may indicate that the increase in intracellular ferritin in the macrophage is in some way related to the secretion of factors by the phagocyte that will stimulate fibrillogenesis by neighboring fibroblats.

Pulmonary complications after subtotal oesophagectomy

The postoperative pulmonary complications in 25 patients undergoing subtotal oesophagectomy for intrathoracic oesophageal carcinoma during the 3-year period 1981-1983 were compared with those of 25 patients undergoing surgery from 1984 to 1986. Although more extensive lymphadenectomies were performed from 1984, the mortality rate caused by the postoperative pulmonary complications was zero in the later period (1984-1986) compared with a rate of 16 per cent in the earlier period (1981-1983). The incidence of postoperative pulmonary complications was lower in the later series but the difference was not statistically significant. Factors which may have contributed to the decrease in critical pulmonary complications after surgery during the later period were the selection of the posterior mediastinal route for reconstruction, the introduction of selective endobronchial intubation by a double lumen tube with combined epidural anaesthesia, fluid restriction during and after surgery, postoperative mobilization and the administration of an expectorant.