36 Colorectal ANATOMY AND PHYSIOLOGY

Colon Structure and Function

• The colon layer that secretes potassium and primarily reabsorbs sodium and water is not specified.
• The rectum is approximately 12-15 cm long from the anorectal ring to the anorectal verge.
• The anterior upper and middle ⅓ of the colon is covered by the peritoneum.
• The transverse bands that form haustra in the colon are known as taenia coli.
• The three longitudinal bands that run along the colon are known as taenia coli.

Colorectal Cancer

• The most common site for primary colorectal cancer is the sigmoid colon.
• The main gene mutation associated with colorectal cancer is APC (adenomatous polyposis coli).
• The #1 site of metastases in colorectal cancer is the liver.
• For potentially resectable isolated liver or lung metastases, the recommended approach is surgical resection.
• The main goal of en bloc resection in colorectal cancer surgery is to remove the tumor and surrounding tissue.
• The standard treatment for low rectal T2 or higher (muscularis propria or greater) cancer is chemoradiation followed by surgery.
• One of the symptoms associated with colorectal cancer is rectal bleeding.

Rectal Cancer

• The anal transition zone is located at the junction of the rectum and anus.
• The recommended repeat colonoscopy interval after removal of 3–10 or advanced adenoma is 3-5 years.
• The most important prognostic factor for colorectal cancer is the presence of lymph node metastases.
• The method best for assessing depth of invasion, recurrence, and lymphadenopathy in rectal tumors is endorectal ultrasound.
• The main nutrient for colonocytes is short-chain fatty acids.

Polyps

• The most common polyp in the colon, with no cancer risk, is a hyperplastic polyp.
• The type of polyp most likely to produce symptoms is a pedunculated polyp.

Blood Supply

• The artery that provides collateral flow between the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA) is the marginal artery of Drummond.
• Sudeck's point is the junction of the SMA and IMA.

Anal Canal

• The nerve that controls the external sphincter (puborectalis muscle) of the anal canal is the pudendal nerve.

Screening and Surveillance

• The primary screening age range for normal risk individuals for colon cancer is 50-75 years.
• The recommended surveillance program for Lynch syndrome patients includes annual colonoscopy starting at age 20-25.

Miscellaneous

• The substance that can lead to false-positive guaiac stool tests is vitamin C.
• The main cause of ischemia in the splenic flexure is atherosclerosis of the SMA.
• The primary method for treating extensive low rectal villous adenomas with atypia is surgical resection.
• The main sympathetic innervation to the colon and rectum is provided by the sympathetic trunk.
• The recommended chemo regimen for postoperative treatment of colon/rectal cancer is FOLFOX or CapeOX.
• The most common cause of death in patients with Familial Adenomatous Polyposis (FAP) following colectomy is duodenal cancer.
• The type of syndrome associated with a predilection for right-sided and multiple cancers is Lynch syndrome.
• The imaging technique that may show a 'bird’s beak sign' in cases of sigmoid volvulus is a barium enema.
• The first-line treatment for cecal volvulus is colonoscopic decompression.
• The symptoms commonly associated with ulcerative colitis are diarrhea, rectal bleeding, and abdominal pain.
• The stage of rectal cancer characterized by distant metastases is stage IV.
• The recommended chemo regimen for pre-operative treatment of potentially resectable rectal cancer is combined 5-FU, leucovorin, and oxaliplatin.
• The type of syndrome associated with a total proctocolectomy requirement after the first cancer operation is Lynch syndrome.
• The imaging technique recommended to confirm the diagnosis of cecal volvulus is CT scan.
• The common feature of Crohn Disease is transmural inflammation.
• The distinguishing feature of Ulcerative Colitis compared to Crohn Disease is the absence of granulomas.
• The distinguishing feature of Crohn Disease compared to Ulcerative Colitis is the presence of granulomas.
• The true statement regarding treatments for toxic colitis and toxic megacolon is that they require urgent surgical intervention.
• The potential surgical indication for ulcerative colitis is refractory disease or bowel obstruction.
• The distinguishing feature of Crohn Disease compared to Ulcerative Colitis is the presence of skip lesions.
• The true statement regarding carcinoid of the colon and rectum is that it is a rare tumor.
• 'Increasing megacolon' is an indication for surgery in ulcerative colitis.
• The true statement regarding the treatment for Pseudo-obstruction of colon in Ogilvie's syndrome is that it is initially managed with supportive care.
• The most common cause of lower gastrointestinal bleeding is diverticulosis.
• The initial diagnostic step to rule out upper gastrointestinal bleeding in diverticulosis bleeding is nasogastric lavage.
• The best initial intervention for massive diverticulosis bleeding with hypotension and tachycardia is fluid resuscitation and transfusion.
• The most sensitive test for intermittent bleeds that are hard to localize in diverticulosis bleeding is tagged RBC scan.
• Angiodysplasia bleeding commonly occurs in the right colon.
• A soft sign of angiodysplasia on angiogram is a tumoral blush.
• The condition most likely to involve the left colon and can be caused by a low-flow state or embolus/thrombosis of the IMA is ischemic colitis.
• The part of the colon most vulnerable to low-flow state in ischemic colitis is the splenic flexure.
• The recommended management for recurrent diverticular bleeds is segmental resection.
• A potential cause of angiodysplasia is aortic stenosis.
• The first-line treatment for uncomplicated diverticulitis is antibiotics.
• The most common location for cecal volvulus is the right lower quadrant.
• The recommended diagnostic test if worried about complicated diverticulitis is CT scan.
• The antibiotic indicated for the treatment of actinomycosis is penicillin.
• In lower gastrointestinal bleeding, what may indicate the diagnosis of upper GI bleeding is a positive nasogastric aspirate.
• The most common complication of diverticulitis is abscess formation.
• The first-line treatment for neostigmine-induced bradycardia in the treatment of cecal volvulus is atropine.
• The artery that provides collateral flow between the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA) in cases of lower GI bleeding is the marginal artery of Drummond.
• The imaging technique recommended to confirm the diagnosis of cecal volvulus is CT scan.
• The primary cause of lower GI bleeding from angiodysplasia, diverticulosis, hemorrhoids, polyps, or cancer is diverticulosis.
• The antibiotic regimen recommended for postoperative treatment of colon/rectal cancer is cefotetan and metronidazole.