Introduction

The obturator vein normally begins in the upper part of the adductor compartment of the thigh and enters the pelvis through the obturator foramen. In the pelvis, it runs posteriorosuperiorly on the lateral pelvic wall and drains into the internal iliac vein. The obturator vein is accompanied by the obturator nerve and obturator artery along its course. Occassionally, an enlarged pubic vein replaces the obturator vein [19, 20].

In research reports and textbooks, variations of veins are given least importance than variations of artries. There are many studies about the origin of obturator artery variations, but studies are lacking on obturator vein termination. The anatomy of the obturator veins is very variable. One of the rare and dangerous variations of obturator vein and its network, is known as “corona mortis” and has been reported occassionally [1,2,3].

Venous anomalies are mainly due to an uncommon selection of channels from the primary capillary plexus during embryonic development of veins. The most suitable channels will enlarge, while others atrophy and disappear, thus providing the means of the final pattern of veins [4, 5].

Presence of any anomalous vessels in the retro-pubic region are at risk during groin or pelvic surgeries because it is very difficult to identify the vessels. Orthopaedic surgeon, urologist, gynaecologist and general surgeons should be aware of unexpected presence these vessels during surgeries [6]. We report a rare variation in the pattern of termination of the obturator vein and discuss its possible clinical implicaitons.

Case report

During our routine dissection classes, we observed an unusual variation of the obturator vein. This variation was found on the right side of the pelvis of a male pelvis aged about 75 years. There were two obturator veins, which entered the pelvic cavity throught the obturator foramen. In the pelvis, the obturator veins ran in posteromedial direction. After a course of 4 cm in the pelvis, they joined with two large vesical veins arising from the inferolateral surface of the urinay bladder to form a vesico-obturator plexus of veins. The components of this plexus surrounded the internal iliac artery and terminated into the internal iliac vein. The obturator nerve and artery had normal origin course and distribution. The variations have been shown in Fig. 1.

Fig. 1
figure 1

Dissection of the variant obturator veins in the right hemipelvis (OF – obturator foramen; ON – obturator nerve; OA – obturator artery; OV1 – first obturator vein; OV2 – second obturator vein; VV – vesical veins; UB – urinary bladder; PLX – vesico-obturator plexus; SCR – sacrum; IIV – internal iliac vein; IIA – internal iliac artery; EIV – external iliac vein; EIA – external iliac artery; A – anterior; P – posterior; S – superior; I - inferior)

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Discussion

Very few variations of obturator veins have been reported in the literature. Termination of obturator vein into the external iliac vein has been reported by Nagabhooshana et al., [7]. In one of the earlier studies, the left obturator vein crossed pelvic brim and terminated into the external iliac vein. This pattern of the vein can affect laparoscopic surgeries and open pelvic brim surgeries [8].

An obturator venous plexus communicating anteriorly with the prostatic and vesical venous plexuses has been reported by Nayak et al., [9]. Such a communicating venous plexus can easily be injured during orthopaedic, gynaecological, and surgical procedures in the pelvic region. Burch procedure is a suspension surgery that adds support to the neck of the urinary bladder and urethra, reducing the chances of stress incontinence. Knowledge of possibility of this type of venous plexus is of importance in Burch procedure, in which, iatrogenic injury to the plexus may lead to hazardous bleeding [10].

Albay et al., [11] noted a venous ring formed by the right obturator vein. The inferior vesical artery originated from the obturator artery instead of the internal iliac artery and passed through this venous ring. The obturator vein is frequently seen to connect with the inferior epigastric vein or the femoral vein [12]. Moore has referred the occurrence of an additional venous connection as the accessory obturator vein [13]. An aberrant obturator vein passing through the obturator foramen and draining into the external iliac vein has also been reported by Kostov et al., [14].

In the current case, we found the duplicate obturator veins forming a vesico-obturator plexus after joining the vesical veins. This is indeed a rare variation and in our literature survey, we could not find any reports on such a variation. Another point of clinical importance here is the relationship of the plexus to the internal iliac artery. A venous plexus surrounding the internal iliac plexus is dangerous as the internal iliac nodes are closely related to it. During iliac lymph node clearance procedure, this plexus could cause unexpected bleeding.

Variations in venous pathways are generally more common than arterial variations, the surgeons should keep in mind its importance to avoid venous bleeding [8, 15]. During pelvic surgeries such as the retroperitoneal lymphadenectomy, anastomosis during a kidney transplant, hypogastric neurectomy and hysterectomy, the internal and the external iliac veins are manipulated frequently. The internal iliac veins are commonly injured during orthopaedic operations involving screw placement [16]. In the repair of inguinal and femoral hernias, knowledge of structures around the pelvic brim and lateral pelvic wall is very important [17]. In this context, the current variation is of importance. Knowledge about these pelvic venous variations is also important to reduce surgical complications and to determine strategy in interventional radiology. Advances in imaging techniques enable to identify venous variations preoperatively [18].

Conclusion

During pelvic and pelvic brim surgeries, particularly hernia surgeries, knowledge regarding variations in the obturator vasculature is very important. Awareness of the current variation of obturator vein could be important in hernia surgeries, orthopaedic and gynaecological procedures. It could also be important in some of the radiological procedures in the pelvic region.