Colorectal

CHAPTER 20
Colorectal


Carlos Glanville, Anton Kelly, and Dale A. Dangleben


Test Taking Tips


• Questions regarding colorectal anatomy, physiology, and pathology are all too common on the ABSITE – while most subjects are fair game there are common themes tested. Comparing and contrasting ulcerative colitis and Crohn disease will always draw a question or two while other benign conditions such as volvulus and diverticulitis will garner questions about nonoperative and operative management.


• Colorectal cancer is a broad topic with many items, which may be tested. Know the proto-oncogenes and tumor suppressor genes associated with the condition, as well as the eponymous diseases, which are risk factors or markers for the development of malignancy. It is also helpful to know the treatment of the different stages of colorectal cancer in regards to neoadjuvant and adjuvant chemotherapy as well as radiotherapy.


ANATOMY AND PHYSIOLOGY


Where does the hindgut begin and end?


Hindgut begins at distal third of the transverse colon and extends to the rectum


The hindgut relies on which artery for its blood supply?


Inferior mesenteric artery


What are the white lines of Toldt?


The lateral peritoneal reflections of the ascending and descending colon


What parts of the gastrointestinal (GI) tract do not have a serosa?


Esophagus, middle, and distal rectum


What are the major anatomic differences between the small bowel and colon?


The small bowel is smooth, whereas the colon has fat appendages (appendices epiploicae), haustra, and taenia coli


What is the arterial blood supply to the rectum?


Proximal: superior hemorrhoidal artery (superior rectal artery) from the inferior mesenteric artery


Middle: middle hemorrhoidal artery (middle rectal artery) from the hypogastric artery (internal iliac artery)


Distal: inferior hemorrhoidal artery (inferior rectal artery) from the pudendal artery, which is a branch of hypogastric artery (internal iliac artery)


What is the venous drainage of the rectum?


Proximal: inferior mesenteric vein that joins the splenic vein to drain into the portal vein


Middle: iliac vein into the inferior vena cava


Distal: iliac vein into inferior vena cava


Image


FIGURE 20-1. Arterial supply to the rectum and anal canal. (Reproduced from Brunicardi FC, Andersen DK, Billiar TR, Dunn DL, Hunter JG, Matthews JB, Pollock RE. Schwartz Principles of Surgery. 9th ed. www.accessmedicine.com. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.)


What is the purpose of the colon?


Water, sodium, and bile salt absorption and stool storage


What is the main nutrient of a colonocyte?


Short-chain fatty acids (SCFA) (butyrate)


How long is the rectum?


12 to 15 cm


What are the approximate proximal and distal extents of the anal canal/rectum/rectosigmoid junction from the anal verge?


Anal canal: 0 to 5 cm


Rectum: 5 to 15 cm


Rectosigmoid junction: 15 to 18 cm


What 2 points are considered to mark the location of the rectosigmoid junction?


The distal point at which the taeniae converge at the level of the sacral promontory


What do anatomists consider the distal extent of the rectum versus what surgeons consider the distal extent of the rectum?


Anatomists: dentate line


Surgeons: proximal border of the anal sphincter complex


What is the eponym for the extension of the peritoneal cavity between the rectum and back wall of the uterus in the female human body?


Pouch of Douglas (Ehrhardt-Cole Recess/rectouterine excavation/rectouterine pouch)


What is the deepest point of the peritoneal cavity in women?


Pouch of Douglas


What is another name for the rectovesicular fascia in men/rectovaginal fascia in women?


Denonvilliers fascia


What is the eponym for a mass that forms in the pelvic cul-de-sac from a drop metastases from a visceral tumor that may be detected by a digital rectal examination?


Bloomer shelf


What is the thick condensation of endopelvic fascia that connects the presacral fascia to the fascia propria at the level of S4, which then extends to the anorectal ring called?


Waldeyer fascia (rectosacral fascia)


What artery is contained within the lateral rectal stalks?


The middle rectal artery


What muscles make up the pelvic floor (pelvic diaphragm)?


Pubococcygeus, iliococcygeus, puborectalis (which form the levator ani)


Where does the pelvic floor (pelvic diaphragm) lie?


Between the pubis, obturator fascia, sacrum, and ischial spines


What artery runs close to the bowel in the mesentery as part of a vascular arcade that connects the superior mesenteric artery and inferior mesenteric artery?


The marginal artery of Drummond


What artery found low in the mesentery, near the root, is part of a vascular arcade that connects the proximal middle colic artery to the proximal inferior mesenteric artery?


The arc of Riolan (meandering mesenteric artery)


What is the most proximal branch of the inferior mesenteric artery?


Left colic artery


Describe the venous drainage of the colon and rectum?


Right and proximal transverse colon drain into the superior mesenteric vein, which joins with the splenic vein to become the portal vein


Distal transverse colon, descending colon, sigmoid, and most of the rectum drain into the inferior mesenteric vein, which drains into the splenic vein that joins with the superior mesenteric vein to become the portal vein


Anal canal drains by way of the middle and inferior rectal veins into the internal iliac veins, which drain into the inferior vena cava


What nodal chain do lymphatics from the colon and proximal two-thirds of the rectum drain into?


Para-aortic nodal chain


What nodal chains do lymphatics from the distal rectum and anal canal drain into?


Para-aortic nodal chain or superficial inguinal nodal chain


What kind of neurologic injury after rectal surgery generally results in sympathetic dysfunction characterized by retrograde ejaculation and bladder dysfunction?


Severing of the hypogastric nerves near the sacral promontory


What kind of neurologic injury after rectal surgery generally results in impotence and atonic bladder?


Injury to the mixed parasympathetic and sympathetic periprostatic plexus


What is the most prevalent species of bacteria in the colon?


Bacteroides species


What is the most common aerobe in the colon?


Escherichia coli


In what colonic segment are bacteria the most metabolically active?


The cecum


How is diarrhea defined?


>3 loose stools/d


How is constipation defined?


<3 stools/wk


What are absolute contraindications to bowel preparation?


Complete bowel obstruction, free perforation


DIVERTICULITIS


How are the diverticula with colonic diverticulosis formed?


Mucosa herniates through the colon at sites of penetration of the muscular wall by arterioles on the side of the antimesenteric taeniae


What area of the colon is most commonly affected by diverticula?


Sigmoid colon (80%)


What segment of the colon has the smallest intraluminal diameter?


Sigmoid colon


What is the treatment for uncomplicated diverticulitis?


Antibiotics on an outpatient basis; if patient has significant pain (localized peritonitis), admit to the hospital and give intravenous (IV) antibiotics for ~48 hours


How should patients be followed after an episode of uncomplicated diverticulitis?


After symptoms have subsided for at least 3 weeks, a colonoscopic examination should be performed to establish the presence/location of the diverticula and to exclude cancer (mimic diverticulitis)


What is the approximate chance of a patient who recovered from an initial episode of uncomplicated diverticulitis developing a second attack of diverticulitis?


<25%


What is the estimated percentage of patients who recovered from an initial episode of uncomplicated diverticulitis requiring a subsequent emergency colectomy or colostomy?


~5%


Although controversial, what types of patients might you offer an elective sigmoid colectomy?


Young patients with an episode of diverticulitis (<45 years old), patients with 2 episodes of diverticulitis, and immunocompromised patients


What is the treatment for an abscess complicating diverticulitis?


The preferred treatment is computed tomography (CT) or ultrasound-guided percutaneous drainage or drainage of a pelvic abscess into the rectum through a transanal approach followed by elective surgery ~6 weeks after drainage of the abscess when the patient has completely recovered from the infection versus a more undesirable transabdominal approach by laparotomy


What are the 2 causes of generalized peritonitis resulting from diverticulitis?


A perforated diverticulum into the peritoneal cavity that is not sealed by the body’s normal defenses; an initially localized abscess that expands and suddenly bursts into the peritoneal cavity


What procedure would you perform for generalized peritonitis from perforated diverticulitis?


A Hartmann procedure: resection of the diseased sigmoid colon; creation of a descending colostomy using noninflamed tissue; closure of the divided end of the rectum with suture/staples


What is the usual time period to wait before restoring intestinal continuity by reversing a Hartmann procedure for perforated diverticulitis?


At least 10 weeks (when patient has completely recovered from their illness)


What is the Hinchey classification grading system for diverticulitis?


Stage I Diverticulitis with associated pericolic abscess


Stage II Diverticulitis associated with distant abscess (retroperitoneal or pelvic)


Stage III Diverticulitis associated with purulent peritonitis


Stage IV Diverticulitis associated with fecal peritonitis


VOLVULUS


What is the most common colonic segment to be involved in a volvulus?


Sigmoid colon


What is the least common colonic segment to be involved in a volvulus?


Transverse colon


What is a cecal bascule?


The cecum folds anteromedial to the ascending colon from the presence of a constricting band across the ascending colon


What findings might you see on plain film, CT scan, and barium enema with a sigmoid volvulus?


Plain film: bent inner tube with apex in the right upper quadrant


CT scan: mesenteric whorl


Barium enema: bird’s beak deformity


What is the treatment for sigmoid volvulus?


Appropriate resuscitation; decompression with placement of a soft rectal tube through the proctoscope past the twist of the volvulus and leaving the rectal tube in place


If a rectal tube cannot be passed, detorsion of the volvulus with a colonoscope


If unable to detorse volvulus by rectal tube or colonoscopy, perform Hartmann operation procedure


Confirm the reduction with an abdominal radiograph, attempt a full colonoscopic examination after cleansing the bowel with cathartics, perform an elective sigmoid colon resection


What is the recurrence rate for sigmoid volvulus without surgical intervention?


~50%


What is a cecal (cecocolic) volvulus?


An axial rotation of the terminal ileum, cecum, and ascending colon with concomitant twisting of the associated mesentery from a lack of fixation of the cecum to the retroperitoneum


What might you see on plain abdominal radiographs with a cecal volvulus?


A gas-filled comma shape with the concavity facing inferiorly and to the right (upside down comma sign), a circular shape with a narrow, triangular density pointing to the right and superiorly, a dilated cecum displaced to the left side of the abdomen


What is the treatment for a cecal volvulus?


The procedure of choice is a right colectomy with primary anastomosis; if frankly gangrenous bowel, resect right colon and create an ileostomy; cecopexy is another option (higher recurrence rates)


OBSTRUCTION


What is the most common cause of large intestinal obstruction in the United States?


Colorectal cancer


What is the most common cause of large intestinal obstruction in Russia, Eastern Europe, and Africa?


Colonic volvulus (high-fiber diets)


What is a closed loop obstruction?


An obstruction featuring the occlusion of the proximal and distal parts of the bowel

Aug 13, 2019 | Posted by in ABDOMINAL MEDICINE | Comments Off on Colorectal
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