Internal Mammary Vein Valves: A Histological Study.

It is widely accepted that the internal mammary vein (IMV) is valveless. However, few anatomical studies are available on the presence or absence of IMV valves. To test the hypothesis that the IMV is valveless, we performed microscopic histological examination of the IMV. IMV samples were collected from 10 human fresh frozen cadavers. For a control, the small saphenous vein (SSV) was obtained. Histological stains were performed. Microscopic examination showed that a venous valve was found in 8 of 20 IMVs. The structure of the valve leaflet consisted of two parts. There was a "thick part" located near the wall of the vein that consisted of smooth muscle cells and fibers. There was also a "thin part" located near the center of the venous lumen that lacked smooth muscle cells. The size of the thick part of the IMV valve was smaller than the SSV valve, whereas there was no difference in the size of the thin part between the IMV and SSV. IMV valves exist. Our results that an IMV valve was present in less than half of IMVs and there was a small-sized valve leaflet suggest that the IMV valve may be rudimentary.