Valves in the iliac venous system were present in 12 (60%) cadavers. These were located in 32.5% of all iliolumbar veins (right: 7; left: 6), 35% of EIV (right: 7; left: 7), 7.5% of CIV (right: 2; left: 1), and 5% of IIV (right: 2; left: 0).
We found a high prevalence of EIV tributaries within the presacral region, the majority of which were sacroiliac and pelvic sidewall tributaries draining laterally. These anatomical variants have not been previously described in the literature. They are critical to pelvic surgeons who fully skeletonize the EIV within the presacral area for vascular control during lateral pelvic compartment exenterations and high/total sacrectomies.13,16–18 The former involves the en bloc resection of lateral pelvic wall structures including the IIV,13,18 whereas the latter may result in extensive hemorrhage that is difficult to control after the patient has been turned prone.11,12,16,17,19 External iliac vein isolation opens a window of safety to visualize the lumbosacral nerve trunk and sacroiliac joint, and prevents inadvertent avulsion and injury during anterior and posterior osteotomies.16,17 If not slung away and protected, unintentional injury to the EIV may predispose to deep vein thrombosis of the lower limb.
Failure to isolate the communicating tributaries may result in incomplete disconnection of the epidural venous plexus and iliac venous systems, resulting in bleeding that is difficult to control if not preemptively addressed. Because the EIV tributaries are small with a mean diameter of 4.0 mm, they are not readily identified on routine preoperative multidetector CT scans. They are also asymmetrical on either side, emphasizing the need for extra vigilance during dissection.
Based on the findings from this study, we have modified our surgical approach to EIV isolation. After controlling the overlying internal iliac artery, dissection begins lateral to the EIV, where the majority of tributaries are found, and where there is usually less tumor-related inflammation. The posterior and medial tributaries are then systematically ligated until the EIV is skeletonized (Fig. 4). In a retrospective study performed in our institution,28 7 and 9 patients underwent urgent and elective sacrectomies and/or lateral pelvic compartment exenterations. Pelvic bleeding was limited by using EIV isolation, with no differences in blood loss and bleeding-related complications found between the 2 groups. This suggests that systematic ligation of the EIV tributaries should be routinely practiced because it is safe and avoids unnecessary bleeding. It does not increase the risk of deep vein thrombosis as long as the main EIV is not injured.
The prevalence of IIV variation in the presacral region in this study was 40%, which is slightly higher than the prevalence reported in the literature (Morita et al,21 30.2%; LePage et al,22 27.0%; Chong et al,23 26.7%; Shin et al,24 20.9%; and Vidal et al,29 16%). There is a multitude of classifications describing the diverse variations of IIV as it drains into the CIV. The classification proposed by Morita et al21 and subsequently elaborated by Chong et al23 had up to 7 IIV patterns, whereas Shin et al24 proposed one with 11 subtypes. These classifications may be useful in academic research but are less pragmatic in clinical practice.
In contrast, the classification proposed, by focusing on the main IIV pattern expected when isolating the IIV from the CIV, is simpler and potentially more practical and relevant during pelvic exenterations. Using preoperative CT imaging,21,24,29 surgeons would be able to anticipate the presence of IIV duplication (type 2) or midline median sacral trunk (type 3) during the initial phase of IIV dissection. Having controlled the main IIV tributary, the individual distal tributaries of the IIV can then be systematically ligated as dissection progresses.18 The frequency of type 2 and type 3 pattern was 35% and 5%, similar to that described by LePage et al22 (27% and 1.2% in 42 cadavers).
The pattern of valves found in this study was comparable to LePage’s study of white cadavers,22 in which valves were located in 26% of EIV, 1.2% of CIV, and 10.1% of IIV. In contrast, previous authors have described that the IIV was avalvular.30 Unlike the superficial and deep venous systems of the lower limb, valves in the iliac venous system are less extensively studied in anatomical or surgical literature. To our knowledge, this is the first report of its prevalence among Asian populations.
The strength of this article lies in the use of unique embalming techniques to create high-quality, soft-embalmed cadavers. This maintains supple and life-like tissue, which, together with the use of blue resin dye to highlight the venous system, helps to accurately identify key anatomical features in comparison with conventional formalin-based embalming techniques.25–27 Despite being limited by a relatively small number of cadavers from a single institution, we are able to demonstrate important anatomical patterns. To understand the true proportion in the general population, larger-scale studies may be helpful. In other articles reporting findings from live surgery,23,29 the respective tributaries of the venous system may not have been traced to their organs of origin for accurate identification. These tributaries may also be distorted by the underlying surgical pathology.
In conclusion, recognizing anatomical variations in iliac vein tributaries is of paramount importance to surgeons performing complex pelvic surgeries. The prevalence of previously undescribed EIV tributaries in the presacral region is high. Classifying IIV variations based on the 3 patterns proposed can potentially facilitate safe dissection and reduce the risk of major hemorrhage. However, general applicability and effects on surgical planning cannot be tested because of the limitations in study design. Larger-scale studies are warranted.
The authors thank Professor Arun Rojanasakul and Professor Tanvaa Tansatit for their assistance.
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