Keywords
external iliac vein - internal iliac vein - histology - pelvis - inferior vena cava
- iliac artery
Introduction
The internal and external iliac veins join to form the common iliac vein, where the
internal iliac vein drains the pelvic region and the external iliac vein is a continuation
of the femoral vein, which drains the lower limb. These two veins join to form the
common iliac vein at the pelvic brim, in front of the lower part of the sacroiliac
joint.[10] The developmental formation of the inferior vena cava (IVC) involves a complicated
process by the involvement of posterior cardinal, supracardinal, subcardinal, subcardinal
and hepatocardiac anastomosis and the hepatocardiac channels. The caudal ends of the
posterior cardinal veins receive the veins draining from the pelvis and from the lower
limb bud. The involvement of these veins in the formation of the IVC and its tributaries,
the multiple connections between these veins, could possibly lead to various anomalous
connections between them, if those developmental connections persist. The remnants
and its connections (if any) demand a need as it is related to clinical importance
and a detailed report regarding these would facilitate clinicians and surgeons to
plan their interventions accordingly.
A catheter generally targeted to pass through the IVC is passed through the femoral
vein, the external iliac vein and the common iliac vein to reach the IVC. Any variation
in this course could lead to life-threatening complications. Variations in the venous
system are reported frequently, but the importance is with respect to the vein presenting
a critical variation possibly hindering a normal surgical or clinical procedure by
a clinician.
Any variation in the normal anatomy of the venous system in this region is related
to the developmental process of the retroperitoneal venous system. It is a complex
process that consists of a network of venous systems appearing during the initial
growth and disappearing at a later stage of the intrauterine life, and this complexity
could explain the variations seen in these veins. The subcardinal, the postcardinal
and supracardinal veins are seen in pairs on either sides of the midline, and the
modifications seen in these sets of veins result in the completion of the development
of the retroperitoneal venous system. These developmental changes generally happen
between the 6th and 8th weeks of gestation.[1]
In retroperitoneal surgical interventions, such as hysterectomy, the relationship
of structures with those considered for surgery play a very important role. Even in
imaging of the pelvis, such as a computed tomography (CT) or magnetic resonance imaging
(MRI), knowledge of these variations could possibly reduce the risk of assessment
that could result in complications.[2] The internal iliac vein may form a venous annulus, which passes around the internal
iliac artery.[1]
In cases of obstruction of the iliocaval segments, the internal iliac vein and its
tributaries provide the vital collateral pathways. This factor along with many clinical
relevance, adds up to the importance for having a normal development pattern in this
venous system.[3] Any complication in the normal anatomy of this venous system could pose potential
problems to clinicians dealing with the pelvis and the structures within the pelvis.
In the present study, we present the involvement of the internal iliac, external iliac
and common iliac veins in a variant formation. This variation in the normal anatomy
of the veins is of considerable importance especially in surgical or radiological
procedures involving the structures present in the pelvic cavity or in the pelvis
itself. The aim of the present study was to note the morphological changes of the
vessels by measuring them and to check the histological features of their walls.
Materials and Methods
During our dissection classes for undergraduate medical students, we observed a unique
variation of iliac vessels in an adult male cadaver aged ∼ 70 years old. The overall
picture of the vessels of the posterior abdominal wall in relation to the variation
is presented here.
The dissection was performed to expose the vessels of the posterior abdominal wall
and the pelvis. The terminal branches of the abdominal aorta were traced until their
termination. The tributaries of the inferior vena cava from their point of origin
were exposed. Relevant photographs of the variations were taken.
The lengths of these vessels were taken using a thread and measured against a normal
measuring scale. The values on the scale were noted down (accuracy of 1mm) and the
recordings involved two persons to avoid any bias. These values were tabulated for
both the right and the left sides. After careful measurement, portions of these variant
formations along with the major veins were taken and processed for normal hematoxylin
and eosin staining procedures. These tissues were fixed with paraffin wax, then sections
were taken using a Leica RM2245 microtome (Leica Microsystems, Wetzlar, Germany).
They were mounted on slides, stained with hematoxylin and eosin. The coverslips were
fixed using dibutylphthalate polystyrene xylene (DPX).
The wall thickness in these stained sections were measured using an ocular micrometer
(Erma Inc., Tokyo, Japan). The values were taken at five different random points that
were approximately equidistant from each other. The average of these measurements
was tabulated.
Results
Morphological Observations
The right and left common iliac arteries were very short, originating from the abdominal
aorta at the level of the 4th lumbar vertebra and were 1.0 cm and 1.5 cm in length, respectively. This short length
of the common iliac arteries led to a higher origin of the internal and external iliac
arteries. Their origins were well above the sacral promontory, resulting in increased
lengths.
The formation and tributaries of the IVC were normal. On the right side, the external
and internal iliac veins had no variations in their normal anatomy. But, on the left
side, an enlargement that could be clearly made out by naked eye observation of the
common iliac vein was noticed.
In contrast, the left internal iliac vein was observed to be narrower than the right
counterpart. The external iliac vein received the obturator, iliolumbar, and superior
gluteal veins. There was also an additional large vein from the psoas major muscle
draining into it. These tributaries, except for the obturator vein, crossed the obturator
nerve and the lumbosacral trunk before they opened into the external iliac vein.
There were two communications seen between the external and internal iliac veins.
This venous ladder-like pattern was located above the level of the sacral promontory.
It was located lateral to the midline and medial to the psoas major muscle.
These aforementioned variations are shown in [Figs. 1] and [2]. The measurements of these veins and the communicating channels between the internal
and external iliac veins are tabulated in [Table 1].
Fig. 1 Dissection of the lower abdomen and pelvis showing the variations of iliac vessels.
The asterisks show three levels of opening of the external iliac vein into the internal
iliac vein. Abbreviations: AA, abdominal aorta; CIA, common iliac artery; EIA, external iliac
artery; I, inferior; IIA, internal iliac artery; IMA, inferior mesenteric artery;
IVC, inferior vena cava; L, left; LCIV, left common iliac vein; LEIV, left external
iliac vein; LIIV, left internal iliac vein; OV, obturator vein; PM, psoas major muscle;
R, right; RCIV, right common iliac vein; S, superior; U, ureter)
Fig. 2 Dissection of the left wall of the pelvis showing unusual tributaries of the left
external iliac vein. Abbreviations: I, inferior; ILV, iliolumbar vein; L, left; LEIA, left external iliac
artery; LEIV, left external iliac vein; LIIA, left internal iliac artery; LST, lumbosacral
trunk; MV, muscular vein from psoas major; ON, obturator nerve; OV, obturator vein;
PM, psoas major muscle; R, right; S, superior; SGV, superior gluteal vein.
Table 1
Table showing the measurements (length) and extents of the left and right external
iliac veins, the upper and lower communicating channels, and the widths of the left
and right common iliac veins close to the point of formation and termination
|
Vein
|
Extent
|
Measurement (cm)
|
|
Left – external iliac vein
|
From LMIP to LC
|
11.0
|
|
Left – external iliac vein
|
Between LC and UC
|
2.5
|
|
Left – external iliac vein
|
Between UC and LCIV
|
1.5
|
|
Right – external iliac vein
|
From RMIP to RCIV
|
15.0
|
|
Left – lower communication
|
From LEIV to LIIV
|
1.0
|
|
Left – upper communication
|
From LEIV to LIIV
|
0.8
|
|
Left – common iliac vein
|
Width – close to formation
|
2.6
|
|
Right – common iliac vein
|
Width – close to formation
|
1.2
|
|
Left – common iliac vein
|
Width – close to termination
|
2.9
|
|
Right – common iliac vein
|
Width – close to termination
|
1.5
|
Abbreviations: LC, Lower communicating channel; LCIV, Left common iliac vein; LEIV,
Left external iliac vein; LIIV, Left internal iliac vein; LMIP, Left mid inguinal
point; RCIV, Right common iliac vein; RMIP, Right mid inguinal point; UC, Upper communicating
channel.
Histological Observations
The measurements were considered in two groups. The first set of values from the normal
common iliac veins, external iliac veins, and then the internal iliac veins. Then
the measurements were taken from the additional communications between the latter
two veins. General microscopic observation revealed the structure of these veins and
the communications to be normal with all the three layers of the wall properly formed,
owing to their normal developmental process. The values of their wall thickness at
five random points of each of the veins so as to cover the complete circumference
are tabulated in [Table 2]. The histological features are shown in [Figs. 3]
[4]
[5]
[6].
Table 2
Thickness of the wall (µ) of the veins at different points and their mean with standard
deviation
|
Serial Number
|
Lower communication
|
Upper communication
|
External iliac vein - left
|
External iliac vein - right
|
|
1
|
0.2
|
0.2
|
0.4
|
0.4
|
|
2
|
0.2
|
0.1
|
0.4
|
0.5
|
|
3
|
0.2
|
0.1
|
0.4
|
0.5
|
|
4
|
0.3
|
0.2
|
0.5
|
0.4
|
|
5
|
0.3
|
0.1
|
0.5
|
0.5
|
|
Mean ± SD
|
0.24 ± 0.055
|
0.14 ± 0.055
|
0.44 ± 0.055
|
0.46 ± 0.055
|
Abbreviations: SD, standard deviation.
Fig. 3 Photomicrograph showing the microscopic structure of the upper communication channel
between the left external iliac vein and the left internal iliac vein.
Fig. 4 Photomicrograph showing the microscopic structure of the lower communication channel
between the left external iliac vein and the left internal iliac vein.
Fig. 5 Photomicrograph showing the microscopic structure of the external iliac vein distal
to the communicating channels (both upper and lower) between the left external and
left internal iliac veins.
Fig. 6 Photomicrograph showing the microscopic structure of the left common iliac vein.
Discussion
The area located between the bifurcation of the aorta above to the pelvic floor below,
with internal iliac vessels on the lateral sides, is known as the presacral area.
The vessels located in this region are prone to high degrees of variation in this
location and there are also reports regarding the variations in the course of the
internal iliac vein in this region.[4]
[5]
According to a previous classification done on internal iliac veins using multidetector
CT by Morita et al,[6] the variations in the formation of the iliac veins were grouped under seven types,
which included dilated Middle Sacral Vein (MSV); on the left - internal iliac vein
connecting with the external iliac vein; on the left - the internal iliac vein with
an isolated trunk terminating into the common iliac vein; a trunk from the right internal
iliac vein terminating into the left common iliac vein; on the right - a trunk separate
from the internal iliac vein draining into common iliac vein; on the right - internal
iliac vein joining the central common iliac vein; on both sides - additional trunks
of internal iliac veins joining with each other and draining into the left central
common iliac vein. These are some of the classifications of the iliac vein variations
found in the literature. Many of the reports have compared and found the variation
under one of these subdivisions. In our case, the multiple connections found in the
veins were not found in our literature search.
The understanding of the development of the venous channels in this region could provide
an insight into the formation of these variations. The lower limb buds drain into
the postcardinal veins, which carry out the function of the inferior vena cava. The
definitive left common iliac vein is formed by the oblique transverse anastomosis
between the iliac veins formed during development. This anastomosis diverts a huge
volume of blood into the right longitudinal veins, which finally account for the disappearance
of most of those veins on the left. Finally, the iliac veins and its bifurcations
remain as one of the derivatives of the postcardinal veins.[7]
[8]
This complicated venous channel anastomosis, appearance and disappearance of veins,
with many venous channels combining to form a single IVC and veins from both sides
joining into this IVC presents a complicated developmental perspective for the veins
in this region. A slight variation in the disappearance of a venous channel could
be a possible reason for the persistence of these communications between the major
veins of the pelvis that drain into the IVC. Although these anomalies generally do
not pose a threat to normal functioning of the system and could be attributed to the
abnormal developmental process, the complications arising in a clinical or in a surgical
environment could not be overlooked. Hence, a detailed knowledge of their presence
and their precise location plays a vital role.
Among the complications involved with the venous channels of the pelvic region, sacral
colpopexy or an extended lymphadenectomy have been reported to be related to massive
bleeding. Complicated vascular structures in this region have been reported in the
literature,[9]
[10] and there exists a possible life-threatening situation due to damage to any of these
complicated vasculatures in this region.[11] It is also said that a careful dissection to expose the anterior longitudinal ligament
of the sacrum prior to the placement of a suture could minimize the complications
of these vascularities. Laparoscopic injuries to the retroperitoneal vessels have
been attributed not only to the insufficient experience but also to the insufficient
knowledge of the anatomy of internal iliac veins.[12] An overall estimate of the prevalence of structural variations of the internal iliac
veins is said to be of ∼ 30.2%, and a surgeon dealing with the pelvic region should
be aware of this increased prevalence of variations. In the pathophysiology of the
Klippel and Trénaunay Syndrome, there is a surgery requiring the intervention of the
internal iliac vein, and in such surgeries,[13] knowledge of any complicated variations like the ones presented here could prove
beneficial for the surgeons. It is also reported that, when placing acetabular screws,
the anterosuperior quadrant of the acetabulum should be avoided to prevent injury
to the tributaries of the internal iliac vein. A medially placed screw could either
penetrate the structures in the area or could be in very close proximity to the tributaries
of the internal iliac vein.
During procedures involving catheters through the femoral vein, there could be complications
involving lacerations of the veins in the procedure.[14] As a result of these lacerations, there could be massive retroperitoneal hemorrhage.[15] It is also suggested that a doctor should ask for help from his colleagues if three
attempts to do so are a failure, owing to the complications involved in these procedures.[16] There are various possibilities for complications in these situations, and our report
adds to the existing knowledge of factors.
In the current case, there were two communications between the external iliac vein
and the internal iliac vein before the formation of the common iliac vein. These two
communications appeared to have a narrow lumen. If the tip of the catheter moves into
such a communicating channel during catheterization, there would be a probable restriction
in passing the catheter and even a slight increased pressure could rupture them.
Histological sections of these communicating channels and the common iliac veins were
performed. Considering the thickness of the venous wall, the layers were normal in
the communications, as well as in the common iliac vein. If these channels had improperly
developed layers, then it could pose even more danger during surgical procedures.
Existence of variations as the one presented in such complicated situations could
pose a serious threat to the patients. The knowledge about the variations of these
venous systems could be of considerable importance in retroperitoneal surgeries, in
certain radiological procedures involving intervention through these veins, and even
in the diagnosis of cancer in the pelvis.
