Investigation of the distribution pattern and structure of lymphatics in the parietal pleura is indispensable to clarify poor prognostic factors of lung cancer such as pleural dissemination and malignant pleural effusion. Using cadavers we investigated by means of the distribution pattern of lymphatics in detail using an enzymehistochemical technique and their structure using light and both scanning and transmission electron microscopy. Initially lymphatics arose from connective tissue just below mesothelial tissue, and though their density varied in different portions, they immediately interconnected to form a plexus. These lymphatics gradually ran into deep layers of the pleura and in the muscular part of the diaphragm connected with conduit lymphatics, which were distributed in parallel to the muscle fibers. The conduit lymphatic vessels drained into several groups in the diaphragmatic pleura: ①towards the lower sternal portion; ②to the boundary adjoining the intercostal pleura; ③to the junction of vertebrae and ribs; ④to the aortic hiatus; ⑤to the esophageal hiatus. Furthermore in the mediastinal pleura there was drainage into; ①the upper and lower portions of the sternum; ②the inferior anterior adjoining the pericardial sac; ③the hilum of the lung; ④the aortic hiatus; ⑤the esophageal hiatus. Using scanning electron microscopy few stoma were observed in the middle of the muscular portion of the diaphragmatic pleura.
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