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Anatomical Variations of Iliac Vein Tributaries and Their Clinical Implications During Complex Pelvic Surgeries

Kanjanasilp, Prapon M.D.1; Ng, Jia Lin M.B.B.S, F.R.C.S.1,2; Kajohnwongsatit, Krittin M.D.1; Thiptanakit, Charnjiroj M.D.1; Limvorapitak, Thitithep M.D.1; Sahakitrungruang, Chucheep M.D., M.Sc.1

Diseases of the Colon & Rectum: July 2019 - Volume 62 - Issue 7 - p 809–814
doi: 10.1097/DCR.0000000000001335
Original Contribution: Colorectal Cancer
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BACKGROUND: During high sacrectomies and lateral pelvic compartment exenterations, isolating the external and internal iliac veins within the presacral area is crucial to avoid inadvertent injury and severe hemorrhage. Anatomical variations of external iliac vein tributaries have not been previously described, whereas multiple classifications of internal iliac vein tributaries exist.

OBJECTIVE: We sought to clarify the iliac venous system anatomy using soft-embalmed cadavers.

DESIGN: This is a descriptive study.

SETTINGS: This study was conducted in Chulalongkorn University, Thailand.

PATIENTS: We examined 40 iliac venous systems from 20 human cadavers (10 males, 10 females).

INTERVENTIONS: Blue resin dye infused into the inferior vena cava highlighted the iliac venous system, which was meticulously dissected and traced to their draining organs.

MAIN OUTCOME MEASURES: Iliac vein tributaries and their valvular system were documented and analyzed.

RESULTS: The external iliac vein classically receives 2 tributaries (inferior epigastric and deep circumflex iliac) near the inguinal ligament. However, external iliac vein tributaries in the presacral area were found in 20 venous systems among 15 cadavers (75%). The mean diameter of each tributary was 4.0 ± 0.35 mm, with 72% arising laterally. We propose a simplified classification for internal iliac vein variations: pattern 1 in 12 cadavers (60%) where a single internal iliac vein joins a single external iliac vein to drain into the common iliac vein; pattern 2 in 7 cadavers (35%) where the internal iliac vein is duplicated; and pattern 3 in 1 cadaver (5%) where bilateral internal iliac veins drain into a common trunk before joining the common iliac vein bifurcation.

LIMITATIONS: This study is limited by the number of cadavers included.

CONCLUSIONS: A comprehensive understanding of previously unreported highly prevalent external iliac vein tributaries in the presacral region is vital during complex pelvic surgery. A simplified classification of internal iliac vein variations is proposed. See Video Abstract at http://links.lww.com/DCR/A900.

1 Colorectal Surgery Division, Department of Surgery, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand

2 Department of Colorectal Surgery, Singapore General Hospital, Singapore

Funding/Support: None reported.

Financial Disclosures: None reported.

Poster presentation at the meeting of The American Society of Colon and Rectal Surgeons, Nashville, TN, May 19 to 23, 2018.

Correspondence: Chucheep Sahakitrungruang, M.D., M.Sc., Colorectal Surgery Division, Department of Surgery, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand 10170. E-mail: chucheep@hotmail.com

The improved morbidity and mortality rates of 25% and 2%1–4 that have been reported in large specialized pelvic exenteration units can be attributed to advances in imaging, better patient selection, modern perioperative chemoradiation, and multidisciplinary surgical techniques. This has led to an increasing acceptance of pelvic exenterations and radical sacrectomies for primary sacral tumors and locally advanced or recurrent colorectal, gynecological, and urological malignancies.5–7 However, surgeons performing complex pelvic surgeries often encounter significant hemorrhage. Vascular injury is a dreaded, life-threatening complication with an incidence of 2.2% to 4.4%.8–10 Increased blood loss is especially associated with lateral pelvic compartment exenterations, total sacrectomies, and high sacrectomies above the level of S3.11–13 The iliac veins are at particular risk because of their location and complex variation.14,15

To avoid uncontrolled hemorrhage, vascular exposure and isolation of the external iliac vein (EIV) and internal iliac vein (IIV) is helpful. This strategy was first proposed by Sahakitrungruang et al,16,17 and similarly described by Austin and Solomon,13 Solomon et al,18 and Warrier et al.19 In performing this step, we have frequently encountered multiple previously undescribed anatomical variations of EIV tributaries in the presacral region. It is important to better understand the anatomy of these tributaries, because they should be preemptively ligated to avoid bleeding.

In addition, surgeons routinely ligate the IIV and its tributaries sequentially to devascularize the pelvis during exenterations and enable safe dissection of the lateral sacral margin during sacrectomies.18–20 Because of its highly variable nature, several classifications of IIV patterns, each with up to 7 to 11 subtypes, have been proposed.21–24 A simple, concise, yet surgically relevant system to approach the dissection of the IIV is needed to promote its utilization in clinical practice. This study on soft-embalmed cadavers was conducted to clarify the anatomical variations of the EIV and IIV relevant to lateral pelvic compartment exenterations, total and high sacrectomies.

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MATERIALS AND METHODS

The iliac venous systems of 20 soft-embalmed Thai human cadavers (10 males, 10 females, mean age 74.1 ± 14.1 years) were examined by surgeons specialized in advanced pelvic exenterations from the Colorectal Surgery Division, Department of Surgery, Chulalongkorn University, Bangkok, Thailand. These cadavers were prepared using special formulations to maintain life-like color and pliability.25,26 Blue resin dye was infused via the inferior vena cava to highlight the iliac venous system and its tributaries.27 The iliac venous system was then meticulously dissected and traced to its draining organs to ascertain their identities and drainage pattern. The veins were bisected longitudinally to identify the presence of valves. The dissection extended from the inferior vena cava to the iliac veins at the level of the inguinal canal inferiorly, and obturator foramen and lateral pelvic wall laterally. Tributaries that drained the gluteal region and pelvic organs were defined as belonging to the IIV. The EIV was defined as starting at the level where the IIV branched from the common iliac vein (CIV). In cases of duplicated IIV, the bifurcation at the proximal IIV was used as the point of origin of the EIV. All findings were recorded using a standardized form accompanied by digital photography. This study was approved by the Institutional Review Board of Faculty of Medicine of Chulalongkorn University.

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RESULTS

Variations in EIV

The EIV classically arises from 2 tributaries (deep iliac circumflex and deep epigastric veins) near the inguinal ligament, with no tributaries within the presacral area. Of 40 iliac venous systems, we found 20 (50%) with tributaries arising from the EIV within the presacral area (15/20 cadavers, 75%). They were asymmetrical on either side in all cases. In terms of decreasing frequency, they were the sacroiliac tributary draining the sacroiliac joint, pelvic side wall tributary, communicating tributary between the ipsilateral IIV and EIV, tributary to S1 root, iliolumbar tributary, and posterior trunk draining several of the above tributaries (Figs. 1 and 2). The mean diameter of each tributary was 4.0 ± 0.35 mm. They arose laterally 72% of the time, whereas 17% and 11% arose posteriorly and medially (Fig. 2).

FIGURE 1

FIGURE 1

FIGURE 2

FIGURE 2

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Variations in IIV

Three main patterns of IIV were observed, as illustrated in Figure 3. Pattern 1 describes the normal anatomy where a single IIV joins a single EIV to drain into the ipsilateral CIV. This was identified in 29 iliac venous systems in 60% of cadavers. Pattern 2, where duplicated IIV tributaries join a single EIV to drain into the ipsilateral CIV, was found in 7 (35%) cadavers. Within pattern 2, 4 cadavers had right IIV duplication, 1 had left IIV duplication, and 2 had bilateral IIV duplication. In pattern 3, the left and right IIV drain into a midline median sacral vein to form a common trunk, with no CIV. This was present in 1 (5%) cadaver.

FIGURE 3

FIGURE 3

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Valves in EIV and CIV

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).

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DISCUSSION

Variations in EIV

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.

FIGURE 4

FIGURE 4

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Variations in IIV

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).

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Valves

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.

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Strengths and Limitations of This Study

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.

Although specialized CT venograms21,24 may provide a more convenient approach to study larger variations of the iliac venous system, they may miss the small-caliber EIV tributaries that can cause significant hemorrhage despite their size. The posterior tributaries, which may be obscured during initial dissection, are more difficult to control when injured. Computed tomographic venograms also add to the contrast-related exposure and burden of cost to the patient.

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CONCLUSION

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.

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ACKNOWLEDGMENTS

The authors thank Professor Arun Rojanasakul and Professor Tanvaa Tansatit for their assistance.

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Keywords:

Cadaver; Iliac vein anatomy; Pelvic exenteration; Presacral area

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