VARIANT BLOOD SUPPLY TO THE DESCENDING COLON, RECTOSIGMOID AND RECTUM BASED ON 400 DISSECTIONS. ITS IMPORTANCE IN REGIONAL RESECTIONS: A REVIEW OF MEDICAL LITERATURE.
Michels et al., 1965, DisColRect, 8: 251-278.
Introduction:
Goligher in 1949 found that 40% of his colorectal anastomosis had dehisced less than one-third to one-fourth posteriorly. He did not attribute this to deficient blood supply but subsequently quoted Lloyd-Davies in a personal communication to him (1954) as saying that this was due to poor blood supply.
Turnbull in 1964 thought that this was due to deficient blood supply and
suppuration of the haematoma behind the anastomosis which would then burst into
the rectal lumen.
Swinton in 1964, considered this complication to be secondary to tension on the
anastomosis and poor blood supply. It is this latter thinking that is persistent these days.
Variant blood supply to the Colorectum is well known. Goligher in a series of 100 dissections found a textbook description of IMA in only 15% while only 5% had a transverse left colic artery. A textbook type of left colic and 1st sigmoid was found in only 40%.
Toupet found the classical type of sigmoid vasculature in only 15%.
We have therefore a situation where standard anatomical textbook descriptions of colorectal vasculature is seriously deficient.
Toupets work on the Sigmoid vasculature found that the sigmoid artery was no
longer than 15 cms and that relative avasculature was present between the terminal branches of the Sigmoid arteries. By resecting the rectum and pulling the Sigmoid down towards the anastomosis, there was potential for kinking of both the Superior rectal and the IMA. This is by far the best rationale one can offer towards a left hemicolectomy procedure as opposed to a Sigmoid utilisation for the colorectal anastomosis.
RESULTS OF THE 400 DISSECTIONS PERFORMED
IMA
IMA has an average length of 3.5 cms (range 2-7 cms) Av diameter is 5 mm (3-8 mm) at the level of L3. Width of two vertebra and two discs which separate the two mesenteric arteries is 7-8 cms. The IMA divides into either -
a) Ascending and descending branch 56%
b) Ascending, descending and middle branch in 38%
c) Anastomosis between ascending and descending branch in 6%.
The Ascending branch reaches the Splenic flexure in 86% and the mid-descending colon in only 14%. This confirms Golligher and Griffiths finding that in only 5% does the ascending branch pursue a transverse course.
The ascending branch gave of mean of 3 branches, middle ramus gave off 2 and the inferior ramus 2.
SPLENIC FLEXURE VASCULATURE
Typically, the ascending ramus of the IMA (left colic artery) divides into right and left branch. The right branch anastomoses with the left branch of middle colic artery. The division into two branches occurs 2-7 cms from bowel wall (average 5 cms) and therefore this bifurcation is critical for maintaining the blood flow to the descending colon. Hence the point of division of the left colic should be proximal to the Griffiths critical point to ensure blood supply from SMA to the descending colon.
Anastomosis between the two branches of the left colic was substantial in 61%, tenuous in 32% and absent in 7%. Disregard of the Griffiths critical point is recipe for disaster.
ABBERENT ARTERIES TO SPLENIC FLEXURE
Because of the intimate relationship of the splenic flexure to celiac axis and its branches, abberent vasculature can occur quite frequently. These are
a) Coeliacocolic trunk.
b) Splenocolic trunk
c) Hepatocolic trunk
d) Pancreaticocolic branch
e) Gastrocolic artery
f) Omentocolic artery.
Marginal link at the splenic flexure is not necessarily made by the union of left branch of middle colic and the right branch of left colic, for any of the listed anomalous colonic arteries many effect this marginal link. A typical example of this is an instance in which the left branch of the middle colic of superior mesenteric origin supplies most of the transverse colon, but does not reach the splenic flexure for at that site vascularisation is provided by a middle colic artery derived from the celiac axis or one of its branches which after leaving the inferior border of the pancreas courses to the splenic flexure and in bifurcating there effects the marginal link by its right and left branch.
SIGMOID ARTERIES
If the sigmoid mesocolon is long and wide, some of the sigmoidal arteries have their origin from the ascending branch of the inferior mesenteric artery (left colic). If sigmoid mesocolon is short and narrow, most of the sigmoid branches arise from the descending branch of the IMA.
Toupet never encountered any sigmoid artery longer than 15 cms, a factor which he considered very important in surgical mobilisation. If the Sigmoid flexure is mobilised to the anocutaneous line, then the point of contact between the 1st and 2nd sigmoid artery is 20-25 cms from the anocutaneous line. Lowering of the sigmoid flexure, in his opinion causes tension on the sigmoid arteries with resultant necrotising vascularisation.
Toupet also found that the marginal artery in the sigmoid is lacking in two thirds of cases and that in many cases there were from two to three weak points in the anastomotic connections between the sigmoid arteries. This is not corroborated in this study.
The authors of this study found six patterns of sigmoid vasculature.
Pattern 1 IMA divides into ascending, mid and descending branch. The mid branch gives of S2 and S3.
Pattern 2 Ascending and S1 are given off conjointly. S2 arises from the loop between S1 and S3 (which is given off from the descending branch).
Pattern 3 S1 is given off higher up from the Ascending branch. S2 from the proximal part of descending. Anastomosis at the distal sigmoid is tenuous.
Pattern 4 S2 is in two branches from the proximal part of descending branch.
Pattern 5 Conjoint origin of Ascending, mid and descending. Mid giving off the S1.
Pattern 6 S1 from Ascending. S3 gives off the Rectosigmoid artery.
RECTOSIGMOID ARTERY
What is the Rectosigmoid?
Rectosigmoid is defined as the area between origin of rectosigmoid artery from S3 (1-2 cms below sacral promontory) and the bifurcation of Superior rectal artery.
What does it supply?
It supplies not only the region of the rectosigmoid but also the upper one fifth of the posterior aspect of the rectum and the upper half of the anterior and sides of the rectum. There is much overlap between the supply and the supply of the Superior rectal artery.
How does it course?
It courses parallel to the rectum unlike the sigmoid vessels which are at right angles to it. It invariably anastomosed with the last sigmoid artery.
How frequently do you see it?
It is present in 64% cases, and vary from 1-3. When it is absent in 36%, the supply is provided by the Superior rectal artery.
SUPERIOR RECTAL ARTERY
Divides opposite S2 or S3 just below the peritoneal reflection. In 81% of cases, it continues as a large right branch of 2-3 mm in diameter and is 12-15 cms long. This right branch supplies the posterior and lateral aspect of the rectal ampulla while the smaller left branch which is regarded as a collateral of the right branch angles forward supplying the lateral and anterior aspects of the ampulla. There are other variants of SRA such as a trifurcating one etc.
IN CONTRAST TO COLONIC VASCULATURE, RECTAL ARTERIES DO NOT FORM ARCADES OUTSIDE THE RECTUM (EXCEPT IN 2% OF CASES WHICH IS WHEN IT CAN BLEED). THEY SIMPLY ENTER THE GUT WALL DIRECTLY AND INDEPENDENTLY.
MIDDLE RECTAL
Middle rectal artery is a branch of the internal iliac commonly in which case it is easy to find and ligate. It can also arise from the Internal pudendal, inferior gluteal, superior or inferior vesical, anterior branch of internal iliac, long vaginal, obturator or the umbilical arteries. In the case of origin from internal pudendal or inferior gluteal, it is difficult to find and is present on the surface of the levator ani. It can be present as one, two or three. On the right side, there are more chances of finding two middle rectals than on the left side. Furthermore, one branch could arise high up from the internal iliac while the other branch could be low down on the surface of levator ani.
In 58% of cases there was a rich anastomotic arcade between the middle rectal and the superior rectal. These anastomosis were sufficient to maintain retrograde flow, but were of small calibre.
Turnbull considers the middle rectal as not so important. He routinely divides the middle rectals on both sides and has found excellent supply to the last 4 inches of the rectum, being supplied retrogradely by the inferior rectal artery.
INFERIOR RECTAL ARTERY
Constantly arises from the internal pudendal, lies below the levator ani and supplies the lower 4 inches of rectum, anal canal and anal sphincter musculature. It divides into three branches. There are numerous twigs given off to the rectum, which can be large, causing disconcerting haemorrhage in LAR.
INTRAMURAL PLEXUS
Vasa recta enter the serosa perpendicularly and form a subserous plexus and then pass directly on to form a submucous plexus from whence it distributes centrifugally to form the myenteric plexus between the longitudinal and circular muscles and centripetally to form the mucosal vascular plexus. The rich intramural plexus with retrograde flow, provides one way in which the blood supply to the colonic wall is maintained despite interruption of the major vascular flow.
VASA RECTA
Compared to the small bowel, there were several differences
a) VR in colon are less numerous
b) VR in colon enter with less angulation
c) VR in colon pierce it farther away from their mesenteric border
d) Longer and more tortuous
e) Less visible anastomosis.
COLLATERAL CIRCULATION
There are 5 types of collateral circulation
a) Between the superior and inferior mesenteric arteries.
b) The inferior mesenteric artery and celiac axis via the aberrantly derived middle colic artery
c) The inferior mesenteric artery and the internal iliac branches
d) The inferior mesenteric artery and the external iliac branches
e) The inferior mesenteric and branches of abdominal aorta.
Note [The arc of Riolan is a communicating loop between the root of Superior mesenteric and the left colic].
Retroperitoneal plexus of Turner [lumbar, ileolumbar, renal, suprarenal arteries from aorta] with the branches of inferior mesenteric artery. In fact there is a much more extensive plexus
1) Twigs from the parietal surface of the abdomen reach the antimesenteric border of the gut.
2) Twigs from marginal arteries or its contributing branches which anastomose with similar branches of Turners plexus such as the fatty capsule of the kidney.
3) Communications between abdominal retroperitoneal branches with the diaphragmatic, intercostals, lumbar and pelvic plexus and with the plexus on the testicular and ovarian arteries and on that of the ureter.
SUMMARY AND CONCLUSIONS
1) Inferior mesenteric artery divided into an ascending (left colic) and descending branch with a middle branch in 38% of the specimens and an anastomosing loop between the two in 6%.
2) The ascending branch reached the splenic flexure in 86% and the mid region of the descending colon in 14%.
3) IMA has 22 divisional patterns.
4) Continuity of the marginal artery at the splenic flexure was substantial in 61%, tenuous in 32% and absent in 7%.
5) The splenic flexure can be supplied by an accessory middle colic artery derived from celiac trunk, hepatic or splenic branch, dorsal pancreatic branch, gastroduodenal or gastroepiploic artery (from the large epiploic arc of Barkow).
6) Sigmoid arteries varied from 1 to 5 (average 3). Derived from ascending, mid or descending branch.
7) Rectosigmoid artery is defined as an artery arising before the bifurcation of the superior rectal artery about 1-2 cms below the sacral promontory and supplying the rectosigmoid and upper one fifth of the posterior aspect of the rectum and the upper half of the anterior and sides of rectum.
8) Gross anastomosis between the rectosigmoid artery, last sigmoid and superior rectal arteries are seen in half the cases.
9) Ligation of main IMA does not lead to vascular compromise because of the retrograde flow through the inferior and middle rectal and from above via the intramural plexus.
10) In most cases Superior rectal bifurcated (81%). It may trifurcate (13%), form loops or undergo multiple divisions.
11) Middle rectal varied from one to three in number on each side and rarely showed symmetrical origin. Of these there were eight different sites. When of high origin they were long, when of low origin, they were short.
12) Branches of middle rectal pass to the bladder, prostate and seminal vesicles or to the uterus and the posterior or lateral surface of vagina.
13) While a grossly visible anastomosis between the superior and middle rectal occurred in 58% all middle rectals joined the intramural submucosal plexus.
14) Anastomosis between the inferior rectal and other rectal arteries was visible in only 14%. Twigs from vesical artery, levator ani vessels and from middle sacral participate in the blood supply.
15) Four intramural plexuses (subserous, submucous, intermuscular and mucosal). These constitue effective rectal collateral pathways. In the colon the vasa recta are less numerous and farther apart than in the small intestine the most common type being the single anterior long branch. They enter the colon at points farther away from the mesenteric border than they do in the small intestine.
16) Collateral circulation of the rectum comprises five pathways
a) superior and inferior mesenteric
b) inferior mesenteric and internal iliac
c) inferior mesenteric and celiac axis
d) inferior mesenteric and external iliac (Lindstrom)
e) inferior mesenteric and branches of aorta the more extensive one in this group is via the retroperitoneal plexus of Turner which communicates the parietal and visceral branches of the abdominal aorta.