Anterior and anterolateral approaches or endoscopic procedures to the lumbar and lumbosacral spine are being done for treatment of different spinal problems with increasing frequency. The introduction of new surgical techniques and more satisfactory results from an endoscopic procedure than from posterior surgery have led to a growing interest in these procedures. However, reported results of anterior and anterolateral surgery have shown that such approaches can be associated with serious complications, including vascular lacerations, neural damage, pleural or abdominal problems, urologic injury, and sexual dysfunction.5,14,17,18,19 The incidence of these complications varies.
Vascular injuries can be arterial or venous in origin. Arterial injuries in the anterior approaches are rare and usually present as thrombotic occlusion9,11,14 or arteriovenous fistulas.1 Venous injuries are more common than arterial injuries, and control of bleeding sometimes is difficult. Venous injuries in anterior spinal surgery include tears to the common iliac vein, inferior vena cava, and iliolumbar vein.3,14 Anatomic variations of the vascular structures in the lumbosacral area can vary substantially among patients. For that reason, preoperative radiologic examination and careful perioperative surgical dissection is recommended. 3,4
The iliolumbar vein is the segmental equivalent for the fifth lumbar vertebra and has no valves.7,12 Injury of the iliolumbar vein may produce massive hemorrhage,3,12 and blood loss may be as much as 1500 cc.14 For that reason, attentive dissection and identification of the iliolumbar vein generally is recommended.10,11,16 Although the importance of the iliolumbar vein is known by spinal surgeons, studies regarding the anatomic characteristics and variations of the iliolumbar vein are rare. Surgeons should be familiar with the detailed anatomic variations of this area. In our literature review, only three iliolumbar vein variations (in two studies) were found.2,12 In a clinical study, it was reported that the variational anatomy in the vessels of the lumbosacral junction are more frequent in males and the overall incidence was 32.3%.8 According to Harmon,8 the iliolumbar tributary is an important part of this vascular system and careful dissection of this vein is necessary. The current study was done to determine the incidence of variations of the lumbosacral vein.
MATERIALS AND METHODS
Thirty-eight iliolumbar veins were dissected from 19 formaldehyde-preserved male cadavers. Meticulous dissection was done for the vascular structure and ×4 loupe magnification was used for the iliolumbar vein. Common iliac, external and internal iliac, and lumbar veins were dissected from the L1 to L4 levels and the ascending lumbar vein was identified by observing the communication of lumbar veins. The obturator nerve and lumbosacral trunk were dissected and identified around the vascular structures.
The diameter and the length of the iliolumbar vein and the distance between the drainage point and the iliac vein bifurcation were measured. The drainage pattern of iliolumbar vein was determined. The relationships of the iliolumbar vein with the lumbosacral trunk, obturator nerve, and iliolumbar artery were ascertained and the distances between them were measured. The angle between the iliolumbar vein and the major vein, into which the iliolumbar vein drains, and the angle between the iliolumbar vein trunk and sagittal plane (medianum planum) were measured and recorded.
The relationships of the iliolumbar vein drainage point and the L5 vertebra’s inferior end plates also were observed, and drainage features and the route patterns were detected and drawn for each dissection.
Means and standard deviations were used as descriptive measures to define variations among the cases.
The iliolumbar vein or veins were detected in both sides of all 19 cadavers. In all cases, the iliolumbar vein was deeper than the obturator nerve. In 12 of 38 cases, the lumbosacral trunk was superficial to the iliolumbar vein. In the other cases, the lumbosacral trunk was deeper when compared with the iliolumbar vein, and the distance between the iliolumbar vein and the trunk was close. The iliolumbar vein was stretched in 12 cases, in which the vein lay deeper than the nerve trunk, when the major veins retracted to the opposite side. In this situation, the distance between the lumbosacral trunk and the iliolumbar vein decreased.
The iliolumbar artery was inferior to the iliolumbar vein in all but five cases. In these five cases, the artery was superior to the vein. The relationship between the iliolumbar vein and the inferior end plate of the L5 vertebra was evaluated. The iliolumbar vein was superior to the L5 vertebra end plate level in four cases; however, in the other cases, the iliolumbar vein was 19.5 ± 13 mm inferior to the L5 inferior end plate. In these four cases, the iliolumbar vein was stretched when the major veins retracted to the opposite side.
Five drainage patterns were seen between the iliolumbar vein and the lumbosacral major veins. Iliolumbar and ascending lumbar veins separately opened into the common iliac vein in 17 cases (44.7%, seven right and 10 left), which was the most commonly seen drainage pattern we saw (Fig 1). It was determined that the ascending lumbar vein joins with the iliolumbar vein by forming one vein, which drained into the common iliac vein in 10 cases (26.3%, five right and five left; Fig 2). The iliolumbar vein rotated posterior, inferiorly, and drained into the internal iliac vein in six cases (15.8%, five right and one left; Fig 3). In two cases (5.3%), the iliolumbar vein drained into the external iliac vein (Fig 4). This anatomic variation was seen on the left side. More than one iliolumbar vein system was observed to drain into the common iliac vein in three cases (7.9%; Fig 5).
In five cadavers, symmetric drainage patterns were seen on the left and right sides. Although in three of five cases the ascending lumbar vein and the iliolumbar vein drained into the common iliac vein separately, in two cases the ascending lumbar vein and iliolumbar vein united to form one branch that drained into the common iliac vein. The right and left side drainage patterns were asymmetric in the remaining 14 cadavers. The distance between the iliolumbar vein and the bifurcation of the inferior vena cava was different between the right and left sides. The other measurements were similar in both sides (Table 1).
The anterolateral retroperitoneal approach to the lumbar spine first was used to treat tuberculosis and was popularized by Hodgson and Stock,9 and described by Hodgson and Wong.10 Anterior approaches to the lumbar spine have had widespread use during the last 10 years for treatment of lumbar scoliosis, fractures, degenerative disc diseases, and segmental instability problems.11,13,14,18 Popularity of the anterior approaches is attributable to availability of interbody fusion devices such as cages, meshes, grafts, and other implants. However, anterior procedures can have dangerous complications including damage to visceral organs, vascular, neurologic, and urologic injuries, abdominal hernia, and sexual dysfunctions.5,14,17,18,19
Vascular injury is a common complication of anterior surgery. The majority of injuries involve perforations or lacerations of veins and arteries. Arterial injury is rare and usually presents as thrombotic occlusion,17,19 or arterial vasospasm.15 If arterial laceration occurs, it most often can be controlled by ligation or electrocauterization. Venous injuries include tears to the common iliac vein and the inferior vena cava and to the iliolumbar vein. 1–6,8,14,18 Venous injuries are more common than arterial injuries. In contrast to arterial injury, venous bleeding sometimes is difficult to control because the veins have thinner walls. At the lumbosacral area, it was shown that the spectrum of individual anatomic variations of the vascular structures is broad and the risk for vascular damage increases with these anatomic variations.4 For that reason, spine surgeons must be familiar with the vascular anatomy of the lumbosacral area.
The iliolumbar vein was equivalent to the fifth segmental lumbar vein and it drained blood gathered from the iliac muscle and inside area of the iliac bone to the common iliac vein.7 In this area, there were no valves in the veins. For that reason, massive hemorrhages could be seen in the vein. Although the iliolumbar vein is an important structure, there are only two published studies regarding this vein.2,12
In 1964, Harmon8 reported on the technique for anterior lumbar disc excision and interbody fusion. He described surgical maneuvers to avoid complications to important structures such as veins in the retroperitoneal area. The incidence of the variations of the lower retroperitoneal veins was 32.3%. In Harmon’s study, the iliolumbar vein was 4–8 mm in diameter and frequently entered the left common iliac vein. He suggested that when the fifth lumbar disc is exposed from the left side, the surgeon should know the iliolumbar tributary. Careful dissection and ligation of this vein are necessary. The anatomic variation was 32.3%; however, anomalies of the inferior vena cava and the common iliac vein also were included, and anatomic variations of the iliolumbar vein were not stressed. However, we found five anatomic variations of the iliolumbar vein, which were not described by Harmon. Venous variations are less frequent in the females because of the larger size of the pelvis which avoids central crowding of structures as they cross the pelvic brim. Large, stocky males require larger veins to handle the effluence from a larger lower extremity muscle mass.8 The real incidence of anatomic variations in humans may be infrequent, as all specimens in our study were from male cadavers. Venous anomalies were more frequent in males in this study, however, because all cadavers were male, no interpretation between genders could be done.
The first anatomic study regarding the iliolumbar vein was reported in 1987 by Arthornthurasook and Gaew-Im,2 who studied 28 sides from cadavers and evaluated anatomic variations of the ascending lumbar and iliolumbar veins with special attention to the site of entry into the common iliac vein. In their study, the ascending lumbar and iliolumbar veins entered the common iliac veins separately in 57.1% of cases whereas they entered as a common stem in 42.9% of cases. They also reported that the anatomy of the ascending lumbar and iliolumbar veins on both sides was identical in six pelves (46.2%), and different in seven pelves (53.8%). All drainage patterns described in their study also were seen in our study. Although our results are similar to results of the study by Arthornthurasook and Gaew-Im, we also saw internal and external iliac vein drainage patterns of the iliolumbar vein and these variations may be the cause of some undefined bleeding.
In 2002, Jasani and Jaffray12 published a more detailed anatomic study of the iliolumbar vein. In their study, 16 iliolumbar vein dissections were done bilaterally on eight cadavers and three anatomic variations were determined. It was shown that a single iliolumbar vein draining into the common iliac vein was the most frequent variation (11 of 16 cases). In other cases, more than one iliolumbar vein drained into the common iliac vein; however, all iliolumbar veins ultimately drained into the common iliac vein in their study. In our study, six cases had drainage into the internal iliac vein and two cases had drainage into the external iliac vein. This difference might be attributable to the fact that we examined more specimens.
There are some limitations of our study. First, formaldehyde-preserved cadavers were used for dissection. In formaldehyde preservation, the dimensions of the soft tissues can change. However, after fine dissection, the position of the vessels and nerves can change with manipulation. For that reason, the dimensions and angular measurements may be different in patients and may not be a guide in surgery. Second, all male cadavers were used in our study. Harmon reported that the ratio of vascular anatomic variations of the lower lumbar area are less frequent in females,8 therefore our results reflect only the variations in the males, not the whole population.
In our study, 38 iliolumbar veins from 19 cadavers were dissected and two drainage patterns were found that were not reported before. This may be attributable to the number of the cadavers used in our study or ethnic or geographic differences or both. In six cases, the iliolumbar vein rotated posteriorly, inferiorly, and drained into the internal iliac vein. This makes dissection difficult in anterolateral, retroperitoneal, and anterior transperitoneal approaches. Additionally, the lumbosacral trunk was placed deep to the vein in 26 of 38 specimens and was prone to complications in anterior and anterolateral procedures.
Anatomic variations of the iliolumbar vein are numerous and must be considered to avoid complications when doing surgery.
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