Exploring the myth of the valveless internal mammary vein--a cadaveric study.

Over the last thirty years the internal mammary system has become the recipient of choice when performing free tissue transfer breast reconstruction. The cranial ends of the internal mammary artery and vein are safely and reliably used for anastomosis following division. Using these cranial vessels maintains their normal antegrade direction of flow. As the complexity of reconstruction has increased, use of the caudal end of the internal mammary vein (IMV) has been cited as a convenient option for additional venous drainage. This requires blood flow in a retrograde fashion. The literature to date suggests that this is possible based on the principle that there are no valves in the internal mammary vein. This will be shown to be incorrect. In this study, the internal mammary veins of 32 formalin-preserved cadavers were dissected to specifically look for and to map valves. 21 valves were discovered in the internal mammary veins of 14 of the 32 cadavers (99 internal mammary veins and major branches). 20 of these were bicuspid in nature, one being tricuspid. Valves were found before or after the branching point of the IMVs, and at multiple sites within some individuals. The significance of valve position relative to rib-space and arborisation of parent IMVs is discussed. Whereas existing data support the use of retrograde IMVs to provide a source of additional venous drainage, we would urge caution in using them exclusively. A proportion of IMVs appear to have valves between the commonly used 2nd or 3rd rib-spaces, and the next draining side-branch.