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Stereomicroscopic funnel-like architecture of pulmonary lymphatic valves.

Although lymphatic valves are basically important in channeling lymph and establishing the lymphatic microcirculation, not much attention has been paid to their structure in the past. They are still classically, and as will be shown, erroneously considered to occur as two semilunar cusps, attached to opposite sides of the vessel wall, and hanging into the vessel lumen like two closely apposed swallow's nests. This widely accepted textbook description (1, 2, 4-7, 15-17, 19, 20) has been largely extrapolated from observations on venous valves situated in the large veins (i. e. the saphenous veins) of the body. Also the appearance of routine histologic tissue sections falsely suggests and mimicks a bicuspid architecture, as our preliminary graphic anatomic reconstructions of 26 pulmonary lymphatic valves from serial (6 μ.) histologic tissue sections have revealed (3, 11, 14). Reconstructed valves seemed to have the shape of a cone or a funnel, oriented obliquely in relation to the axis of the vessel and attached over its entire length to the wall of the vessel. The lumen appeared to be situated near the deepest point of the funnel. These anatomic graphic reconstructions were however only an indirect, probably a more or less biased approach to the real architecture of the pulmonary lymphatic valves. Indeed, due to their overall dimensions and their specific "intra vascular" localization, it was impossible to locate accurately the reference points which are an essential condition in anatomical reconstructions. Even if major deformations could be avoided due to the inherent complexity of the lymphatic vessel network and of its valves, and because of the rather limited number of the 6 micron sections used for the actual reconstructions ( 18), slight lateral deformations were unavoidable. Moreover (3), still another cause of artefactual lateral deformation, lenghtening and stretching of the graphic models, occurred because we reconstructed in perspective under a very large angle rather than by orthogonal projection. Hence our graphic anatomic reconstructions did not constitute an exact replica of reality and were undoubtedly subject to various artefacts to some extent. Therefore the present study was undertaken in order to correct these earlier results. As only a direct observation of the lymphatic valvular architecture seemed appropriate, we studied lymphatic valves stereomicroscopically on single and serial 150-250 micron thick histologic sections through the entire lung lobes.