Great Saphenous Vein Lumen: Intimal Openings.

This review discusses the morphological characteristics of the human great saphenous vein (SV) harvested for coronary artery bypass grafting (CABG). It focuses on the vein's luminal intima, which was examined using laser confocal microscopy (LCM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Summarised findings are: (1) LCM observations revealed that the vessel-like profiles, formed by the intima of the peripheral parts of SV luminal folds, may create a false impression that these are vasa vasorum vessels terminating at the vein lumen. (2) The SV luminal intima displays openings ranging from about 5 μm to 20 μm. Among these, larger openings (> 10 µm) are recognized as openings of small tributary branches rather than vasa vasorum vessels donating to SV lumen. It is suggested that these vessel openings are involved in the retrograde blood flow into the SV graft wall after CABG. In contrast, openings < 10 µm, or even those < 5 µm, did not show obvious vascular characteristics, suggesting these structures might have another physiological function. (3) In addition to the abovementioned openings, narrow, elongated intimal openings approximately 3 μm by 30 μm in size can be seen at the SEM level; these likely represent the entrances to the small folds detected by TEM in the inner media of the SV. Communication between the SV lumen and the vein vasa vasorum seems crucial for the anti-ischaemic protection of the vein as coronary graft. This issue, including the role of intimal openings, may require further investigation.