Anatomy and Physiology
Venous drainage of the abdominal viscera is produced by a series of veins that end into the portal vein.
Although there are many anatomical variants,
usually the inferior mesenteric vein and splenic vein converge to form the splenomesenteric trunk.
Then this trunk joins the superior mesenteric vein to form the portal vein.
In turn,
these major veins are formed by the confluence of minor veins.
Typically,
the venous system is satellite to the arterial one.
This justifies the evaluation of the arterial vessels alone (using a CT angiography,
accompanied by maximum intensity projection and volumetric reconstructions).
However,
due to tumor pathophysiology,
drainage and potential extension distance is performed through veins and lymphatics (running parallel to the veins).
Therefore,
for the study of tumor spread and potentially adequate resection of tissues affected by neoplasia,
the knowledge of the venous anatomy is particularly interesting.
As said,
the venous system usually runs parallel to arteries,
so the study and knowledge of the arterial anatomy are often enough.
However,
there are two locations where this is not the case: gastrocolic trunk of Henle and splenic flexure.
Gastrocolic trunk of Henle (see Figure 1):
This is a tributary of the superior mesenteric vein.
It is formed by the confluence of right gastroepiploic vein,
superior anterior pancreatoduodenal vein and upper right colic vein.
Although this is the most common anatomical variant,
there is wide variability.
Other veins that can lead to the venous trunk are the right middle colic vein and the middle colic vein.
Splenic flexure (see Figure 2):
The description of this anatomical region is very important for surgical treatment.
The course of the inferior mesenteric vein from the rectum to the middle colic artery occurs close to the inferior mesenteric artery.
However,
there is a fragment (from this point to the lower edge of the pancreas) in which the inferior mesenteric vein is not accompanied by an artery.
Surgical importance and contributions of Radiology
Surgical importance is that adequate knowledge of the venous anatomy allows excision of the mesocolon territory corresponding to drainage of the tumor,
where there is potential spread of disease.
Different studies in Europe and Japan show increased survival of patients having a wide resection of the part of the mesocolon where the tumor drains.
Radiological image techniques (contrast injected CT) are the key to diagnosis and staging of the tumor,
and also play an increasingly relevant role in successful treatment.
A study in venous phase with multiplanar and volumetric reconstruction of the veins,
allows to inform the surgeon about anatomical variants and detail the route of abdominal visceral veins,
with special emphasis on those territories where the venous circulation does not runs satellite to the arterial system.
Currently,
in addition,
these three dimensional models can become real models using 3D printing,
which helps the surgeon to spatially locate these structures and improve surgical planning (see Figure 3).
Another contribution of Radiology is knowledge of postsurgical anatomy (see Figure 4).
Reconstructions of veins using maximum intensity projections and volumetric projection allow study of venous vascular permeability after surgery.
This postoperative reconstruction could be used as a surgical quality criteria to show if the tumor drainage veins have been resected or not.
For illustration presented,
as shown,
the superior right colic vein has been resected.
According to some authors,
this vein should be incorporated into a right hemicolectomy for adequate lymphadenectomy and complete excision of the right mesocolon.
Importance of the knowledge of the anatomy of gastrocolic trunk of Henle (see images 5,
6 and 7)
Studies have shown that techniques that resection of more lymph nodes correlates with survival in the treatment of colon cáncer.
In order to resect a greater number of lymph nodes,
new techniques have been born D3 lymphadenectomy (D3-L) and complete excision of the mesocolon. Both techniques have in common the proximal clamping of the arteries.
D3 lymphadenectomy (D3-L),
highlights the need to incorporate the nodes located in proximity to the superior mesenteric vein,
particularly in two regions:
● Surgical area of gastrocolic trunk of Henle.
Right superior colic vein should be incorporated into the surgical specimen.
● Lymph and fat tissue on the lateral side of the superior mesenteric vein.
Lymphadenectomy D3 (D3-L) and dissection gastrocolic trunk of Henle (GCTH) during right hemicolectomy for right colon cancer have been proposed in order to reduce the rate of local recurrence.
Anatomic location,
vascular variability and fragility of the veins in this area increase the risk of intraoperative bleeding during the performance of these techniques.
The preoperative radiological study is essential to reduce the risk of bleeding and avoid fatal consequences for the patient.
Importance of the knowledge of the venous anatomy of the splenic flexure (see images 8,
9 and 10)
A definition of splenic flexure can be performed based on anatomical criteria (between the distal third of the transverse colon and proximal descending colon) or based on their irrigation (colonic territory irrigated by the left branch of the middle colic artery and the left colic artery).
Currently,
three different types of oncologic resection of colon adenocarcinoma splenic flexure (AEA) are used,
depending on blood vessel ligation:
● Segmental resection of the splenic flexure. From the left branch of the middle colic artery to the left colic,
with subsequent anastomosis.
● Left hemicolectomy. From the left branch of the middle colic artery to the root of the inferior mesenteric artery,
with subsequent colorectal anastomosis.
● Extended left hemicolectomy. From the root of the middle colic vessels to the root of the inferior mesenteric artery.
None of the three techniques has shown advantages on tumor recurrence rate or on survival.
Indeed,
some authors have described the presence of affected lymph nodes on the right side for neoplasms of splenic flexure,
so they defend performing subtotal colectomy with ligation of ileocolic vessels,
right colic artery,
middle colic vessels and left colic artery at its root.
Given the disparity of criteria when tilted by a surgical technique or another,
seems reasonable to look for anatomical criteria taking into account the possible venous drainage and thus lymphatic drainage of the tumor,
in order to select the most appropriate surgical technique.
Different imaging and pathological techniques (indocyanine green / sentinel lymph node) have demonstrated the presence of lymph nodes in the portion of the inferior mesenteric vein located at the splenic flexure.
It seems appropriate to incorporate this segment of the inferior mesenteric vein in the surgical specimen.
Like this,
the greatest possible number of potentially affected lymph nodes will be resected,
obtaining increase on patient survival in relation to their oncological process.
At the same time,
this ensures the best possible surgical technique,
reducing surgical bleeding and improving postoperative healing.