and Edgar D. Guzman-Arrieta3
(1)
Department of Surgery Advocate Illinois Masonic Medical Center, University of Illinois Metropolitan Group Hospitals Residency in General Surgery, Chicago, IL, USA
(2)
University of Illinois at Chicago, Chicago, IL, USA
(3)
Vascular Specialists – Hattiesburg Clinic, Hattiesburg, MS, USA
Keywords
ColonRectumAnusColectomyColon resectionColonic anastomosisSphincterotomy1.
Select the true statement.
(a)
Auerbach’s plexus is located in the submucosa.
(b)
Meissner’s plexus is located in the muscularis propria.
(c)
Absence of parasympathetic ganglia causes a segment of the bowel to be contracted and unable to conduct peristalsis.
(d)
Aganglionosis is the sole cause of megacolon.
(e)
In Hirschsprung’s disease, the dilated colon lacks ganglion cells.
Comments
The enteric nervous system is composed of a large population of diverse neural crest-derived cells forming complex plexuses within the bowel wall. While this network is subject to higher neurological and endocrine signals, it is also capable of functioning independently in regulating motility, secretion, and blood flow in the GI tract.
The midgut and hindgut are under the influence of the autonomic nervous system. The vagus nerve and the sacral plexus provide parasympathetic innervation and, in general, promote secretion, absorption, and peristalsis. In opposition, the sympathetic fibers derived from the thoracic and lumbar spinal cord inhibit peristalsis, increase the tone of the sphincters, and decrease secretion and absorption [1].
The foregut and midgut are colonized in craniocaudal fashion by neural crest cells originating in the vagal nuclei, whereas the hindgut is colonized from the sacral neural crest at a slightly later stage in development. These cells appear to migrate following chemotactic signals in the form of glial cell-derived neurotrophic factor (GDNF), which binds the product of the RET proto-oncogene. Interestingly, RET mutations are the chief genetic defect associated with Hirschsprung’s disease. These mutations explain the association of Hirschsprung’s disease and MEN2A syndrome [2–4].
Auerbach’s plexus is located between the circular and longitudinal muscular layers, while Meissner’s plexus resides in the submucosa. Additionally, a distinct population of glial cells located in the outer submucosa forms Schabadasch’s plexus. While the function of these plexus was thought to be related to their location (i.e., Auerbach’s for motility and Meissner’s for mucosal secretion), it appears that both are highly interconnected and participate jointly in the regulation of all bowel functions, while coordinating afferent signals from the autonomic nervous system [5, 6].
Hirschsprung’s disease is characterized by an absence of ganglion cells (involving both Meissner’s and Auerbach’s plexuses) in the affected segment of the colon. As a result, the affected segment is unable to relax creating a functional obstruction. Aganglionosis most often affects the distal hindgut; however, the absence of ganglion cells has been demonstrated in the proximal colon and small bowel. While the bowel proximal to the zone of aganglionosis is histologically normal, it often suffers passive dilatation secondary to a distal functional obstruction. Differential diagnoses include constipation, meconium ileus, meconium plug, small left colon syndrome, and intestinal neuronal dysplasia, making biopsy necessary to confirm the diagnosis [7, 8].
In the United States, Chagas disease is seen as a cause of megacolon with increasing frequency in relation to immigrants from endemic areas (Brazil, Argentina, Peru, and Bolivia). This disease is caused by Trypanosoma cruzi, an intracellular parasite with affinity for cells of the autonomic nervous system. This protozoan causes “mega” syndromes affecting the heart, esophagus, small bowel, and colon.
Answer
c
2.
The lymph nodes draining the colon are classified into the following groups except:
(a)
Epiploic – Along the greater omentum
(b)
Epicolic – On the colonic wall, beneath the serosa
(c)
Paracolic – Along the marginal artery of Drummond
(d)
Intermediate – Along the colonic branches of the superior and inferior mesenteric arteries
(e)
Pre-/para-aortic – At the root of the superior and inferior mesenteric arteries
Comments
Interest in the anatomy of colonic lymphatics has increased due to the well-established association between the number of lymph nodes obtained in a colon cancer resection and survival. It has been well established that adequate colon resections should contain 12 or more lymph nodes. It is possible that greater lymph node retrieval may result in survival improvements [9]. In addition, there is currently interest in the role of sentinel node mapping in the treatment of colon cancer, although its practical application has not been fully defined [10, 11]. Colon lymphatics are categorized in a four-tier system including epicolic, paracolic, intermediate, and pre-/para-aortic nodes. While these node levels form a concentric pattern, lymphatic drainage is not necessarily radial towards the preaortic nodes. On the contrary, lymph may flow cephalad or caudal along a given level, generating anomalous drainage patterns [12] (Fig. 15.1).
Fig. 15.1
Lymphatic drainage of the colon parallels the superior and inferior mesenteric vein tributaries through pericolonic and intermediate nodes to the preaortic lymph nodes. Lymphatic drainage of the rectum follows through the mesorectal nodes to the preaortic nodes. Ectodermal anus and anal canal neoplasms as well as very low rectal neoplasms may spread to the inguinal and mesorectal lymph nodes, similar to the dual portal and systemic venous drainage of this area. Eventually all lymphatics will reach the thoracic duct via its intestinal or lumbar trunks and veins to the hepatic portal system via mesenteric veins
Answer
a
3.
All of the following are correct except:
(a)
The marginal artery of Drummond communicates the ileocolic, right colic, middle colic, left colic, and sigmoid arteries.
(b)
The arc of Riolan is an inconstant vessel communicating the IMA and SMA along the distal transverse mesocolon.
(c)
The critical point of Sudeck marks the place where the superior rectal artery can be ligated without devascularizing a long rectosigmoid stump.
(d)
The right mesocolon is less vascular than the left, hence the preference for the former when executing retrocolic gastrojejunostomies.
(e)
Each epiploic appendage has its own blood supply and its torsion will produce infarction.
Comments
Please see question 4.
Answer
d
4.
All of the following are correct except:
(a)
A watershed area for vascular, lymphatic, and neural supply exists at the junction of the middle and distal thirds of the transverse colon.
(b)
The upper rectum drains into the inferior mesenteric nodes.
(c)
Anastomosis between the superior and middle and inferior rectal veins constitutes a site for portosystemic shunting responsible for secondary hemorrhoids.
(d)
Testicular cancers drain into the inguinal lymph nodes.
(e)
The distal anal canal drains into the inguinal lymph nodes.
Comments
The three main mesenteric vessels (celiac trunk, superior mesenteric artery (SMA), and inferior mesenteric artery (IMA)) are connected by ample anastomotic networks. These networks allow communication between branches as well as between the mesenteric and systemic circulations. Their capacity to accommodate blood flow is illustrated by the fact that the lower extremities may be perfused through branches of the inferior mesenteric artery in aortoiliac occlusive disease.
In the colon, the main anastomotic network is formed by the marginal artery of Drummond, which lies in proximity to the colon and gives rise to the vasa recta. This vessel communicates the branches of the SMA and IMA. The arc of Riolan (also known as meandering mesenteric artery) is a less constant anastomosis between the middle colic and the left colic artery. It lies closer to the root of the mesentery than the marginal artery of Drummond. Enlargement of these vessels reflects the presence of collateral flow due to vascular occlusion. Absence of this anastomosis may occur in up to 50 % of cases, creating a watershed at the splenic flexure. Due to its vulnerability to ischemia induced by colonic resections, this area has been named the “Griffiths’ critical point” [13–15]. The left mesocolon has less collaterals than the right; as such, it is the preferred side for tunneling retrocolic anastomosis.
The critical point of Sudeck was described at the beginning of the twentieth century in an effort to promote the viability of the rectosigmoid stump in left colic resections. At the time, it was thought necessary to preserve the most distal arcade of the rectosigmoid vessels by ligating the superior rectal artery proximal to it. However, intramural collaterals of the rectosigmoid can preserve a stump extending up to 8–10 cm from the peritoneal reflection, making the critical point of Sudeck an item of historical interest [16, 17].
Epiploic appendages are fat-filled sacs of visceral peritoneum supplied by terminal vessels independent of the colonic wall circulation. This determines that appendagitis will not result in colonic perforation. They number approximately 100 in the normal individual and are most abundant in the sigmoid colon (57 %) and cecum (26 %) [18].
The blood supply and lymphatic drainage of the anorectum reflect its origin from two distinct embryologic entities, namely, the distal hindgut (endoderm) and the anal pit (ectoderm). As such, blood supply to the proximal anorectum is provided by the superior rectal artery, which is the terminal branch of the inferior mesenteric artery. This artery extends distally to the dentate line, which marks the endoderm–ectoderm junction. Lymphatic drainage for this segment is directed towards the mesenteric nodes. The middle sacral artery arises from the posterior wall of the distal aorta and provides blood to the posterior wall of the rectum and upper anal canal.
In contrast, blood supply to the anorectum distal to the dentate line is provided by the paired middle and inferior rectal arteries, both branches of the internal iliac (pudendal) arteries. Lymphatic drainage of this area is towards the inguinal nodes, constituting an exception where lymphatic drainage does not follow the blood vessels. Like anal cancers, vaginal, scrotal, and perineal malignancies drain into the inguinal lymph nodes. On the other hand, testicular cancers, like ovarian cancers, drain to the preaortic nodes. Of note, the rectal arteries and veins also receive the name “hemorrhoidal” [19] (Fig. 15.2).
Fig. 15.2
The anorectal area has dual lymphatic and venous drainage. The rectum largely drains into the preaortic nodes after going through the mesorectum, while the anal canal and an overlapping junctional zone may additionally drain into inguinal lymph nodes along the middle and inferior rectal veins. To properly harvest these nodes, an en bloc total mesorectal excision is the standard of care for resectable tumors of the rectum which have infiltrated past the mucosa
Answer
d
5.
All the following are correct except:
(a)
Interposition of the bowel between the liver and diaphragm may be confused with pneumoperitoneum.
(b)
Pneumoperitoneum may be asymptomatic.
(c)
The ascending or descending colon may interpose in retrorenal position.
(d)
Posterior perforations of the colon remain confined to the retroperitoneum.
(e)
Pneumoscrotum after colonoscopy suggests perforation.
Comments
The hepatic flexure of the colon or other segments of the bowel may become interposed between the liver and the diaphragm, giving the appearance of free air on plain abdominal films, a finding known as Chilaiditi’s sign. This can be accompanied by episodic abdominal pain and has been named Chilaiditi’s syndrome. Confirmation of the diagnosis can be made by CT scanning. It is important to note that the presence of Chilaiditi’s sign does not rule out the coexistence of other abdominal pathologies, and diligence should be exercised in finding the cause of coexisting symptoms [22–24].
Pneumoperitoneum does not always warrant abdominal exploration or signify hollow viscus perforation, especially in an asymptomatic patient. Cases of spontaneous pneumoperitoneum have been described in female runners, pneumatosis intestinalis, and extension from the thorax and mediastinum as well as after cunnilingus.
The colon may come to occupy anomalous positions in the abdomen due to alterations in normal bowel rotation. Instances of retrogastric, retrosplenic, retrohepatic, and retrorenal colon have been described. While these conditions are most often asymptomatic, they should be considered when interpreting imaging studies as well as before embarking on interventional procedures [25–27].
Posterior perforations of the colon can create contamination of the retroperitoneum with secondary infection of the structures therein. The most common cause of perforation in the western hemisphere is diverticulitis. Often, this condition presents with contained perforations in the pericolonic fat. It should be noted that these are pseudodiverticula, as their wall does not contain all three layers of the normal colonic wall. Rather, these are mucosal herniations through sites of perforator blood vessel entry (Fig. 15.3).
Fig. 15.3
Classic diverticular disease of the colon actually represents pseudodiverticula as they do not own a muscle coat and hence are unable to contract or empty themselves. The neck of each diverticulum has an intracolonic artery sharing the same defect through which the mucosal diverticulum protrudes out. This is the same artery which when eroded in diverticular disease causes hemorrhage and, in cases of diverticulitis, undergoes thrombosis contributing to micro-perforation and resultant abscess formation. S serosa, L longitudinal muscle coat, C circular muscle coat, LP lamina propria, M mucosa, ICA intracolonic artery
Answer
d
6.
The following are landmarks for the junction of the sigmoid colon and rectum except:
(a)
3rd sacral vertebra
(b)
Level at which the sigmoid mesentery disappears
(c)
Sacral promontory
(d)
Level at which the taenia coli coalesce
(e)
Level at which the superior rectal artery divides
Comments
Please see question 7.
Answer
c
7.
Select the true statement regarding the anal canal above and below the dentate line.
(a)
Below the dentate line, the anal canal has simple columnar epithelium.
(b)
The most common form of cancer above the dentate line is squamous cell carcinoma.
(c)
The most sensitive part of the anal canal lies above the dentate line.
(d)
The most common cancer below the dentate line is treated with the Nigro protocol.
(e)
Circumferential stapled hemorrhoidopexy is an ectodermal operation.
Comments
Like with the gastroesophageal junction, multiple and sometimes conflicting landmarks have been cited to describe the limits of the rectum. The junction of the sigmoid colon and rectum is best defined by the coalescence of the taenia coli into a continuous longitudinal muscle layer. This distinction is very important in the setting of colonic diverticulosis, which by definition does not cross over to the rectum. The level of this transition, as well as the level of the peritoneal reflection, is subject to individual variations. There tends to be a concordance between the disappearance of the sigmoid mesentery, the uppermost valve of Huston, and the upper border of the third sacral vertebra as useful landmarks between the sigmoid colon and rectum.
Distally, the dentate line and the uppermost aspect of the anal sphincter complex have been cited as separating the rectum from the anal canal. This distinction becomes less important when the anorectum is considered as a functional unit. However, the sphincter complex and its function must be considered when contemplating the different options for surgical excision.
On the other hand, the dentate line is useful when considering the type of epithelium and malignancies derived thereof. The epithelium above the dentate line is derived from the hindgut endoderm and is columnar. Below the dentate line, it is derived from the ectoderm and is squamous. In between the two, there is a transition zone, whose behavior more closely resembles that of the endoderm. Functionally, it is thought that the transition zone serves an important role in sensing the nature of the rectal contents.
In concordance with the above division, the sensory nerve supply above the dentate line is autonomic and allows essentially pain-free procedures at this level (internal hemorrhoid banding and stapled hemorrhoidopexy). In contrast, the epithelium below the dentate line has a rich somatic nerve supply, making it very sensitive and explaining the symptoms originated by pathology in this area [34, 35] (Fig. 15.4).
Fig. 15.4
The anorectal junction is marked by the dentate line, which represents a series of pockets called crypts. Each pocket is suspended at the bottom of two mucosal pleats named the columns of Morgagni. Inside the crypts are the openings of the anal glands, which secrete mucous to help lubricate the anus as the sphincter relaxes during a bowel movement. The corrugator cutis ani muscle is the insertion of the longitudinal muscle coat and, as the name implies, is responsible for corrugation of the immediate perianal skin
The most common cancer of the anal canal is squamous cell cancer. Unlike anal adenocarcinoma, which requires surgical excision, squamous cell carcinomas are primarily treated with radiation and chemotherapy (Nigro protocol), with surgery reserved for treatment failures and recurrences. Current recommendations advocate the use of mitomycin combined with 5-FU and 5,000 Rads. Bowen’s disease is anal squamous carcinoma in situ. It does not require treatment using the Nigro protocol; rather, it is treated with topical 5-FU and close follow-up.
Melanoma of the anal canal is a rare tumor. Its treatment is based on the principles guiding the management of cutaneous melanoma, that is, wide excision and sentinel node mapping and excision [36].
Answer
d
8.
Match the following tumor locations with the most appropriate operation
(a) Cancer of the cecum | 1. Left hemicolectomy |
(b) Cancer of the mid transverse colon | 2. Low anterior resection |
(c) Cancer of the proximal rectum | 3. Right hemicolectomy |
(d) Cancer of the descending colon | 4. Extended right hemicolectomy |
(e) Cancer of the distal rectum | 5. Abdominal perineal resection |
Comments
The surgical treatment of colorectal cancer (open or laparoscopic) is based on the vascular pedicles to different sections of the colon and the associated lymphatic drainage basins. While at least 2 cm distal margin of resection must be considered, they rarely become determinants of the extent of resection. Colon cancer tends to have more proximal than distal spread, determining recommendations of 5–7 cm proximal margins. Surgery of the rectum and anus must take into account the involvement of the sphincter complex.
Right hemicolectomies resect the segment supplied by the ileocolic and right colic artery, while left hemicolectomies involve the territory of the left colic artery. Either resection may be, respectively, “extended” to the territory supplied by the right or left branch of the middle colic artery. The sigmoid colon may be resected independently.
Resections of the rectum must consider the distance between the tumor and the sphincter complex. Again, at least a 2 cm margin must be achieved, determining that if such margin is obtainable, a low anterior sphincter preserving resection should be performed. In contrast, if this margin does not exist, and more so if the sphincter complex is involved, an abdominoperineal approach must be taken [37–39] (Fig. 15.5a, b).
Fig. 15.5
(a) Surgery for cancer of the right colon consists of removing the right colon en bloc with its lymph node drainage basin along the ileocolic and right colic bundles, and ending to the right of midcolic vessels. Similarly, left hemicolectomy is for cancers of the left colon removing lymph node drainage basins from left of the midcolic vessels and including the left colic and first branches of the sigmoid vessels. Cancer of the transverse colon between the two flexures may require extended right or left hemicolectomy including midcolic lymph node basins. IC ileocolic vessels, LC left colic vessels, MC middle colic vessels, RC right colic vessels, IMA inferior mesenteric vessels, SMA superior mesenteric vessels. (b) Low anterior resection refers to the removal of the rectosigmoid through an anterior abdominal approach as compared to the abdominoperineal resection where an additional perineal approach is added to remove the perianal skin, anorectal canal, and ischio-anal fossa contents of fat and lymph nodes. En bloc resection of the mesorectal pad of fat and lymph nodes is part of both procedures. SMA superior mesenteric vessels, IMA inferior mesenteric vessels, RC right colic vessels, MC middle colic vessels, LC left colic vessels, IC ileocolic vessels, RA anorectum with ischiorectal tissues, MR mesorectum
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