Ch 13: Large Intestine Part 1

Question 1

Newborn shows features of Down Syndrome. After 2 days, the baby has failed to pass meconium and is vomiting. The rectal vault is empty, and imaging studies show a massive dilation of the colon prior to a narrowed rectum. What is this disease and what is the pathogenesis?

Answer 1

Congenital megacolon/Hirschsprung disease - defective relaxation and peristalsis of rectum due to failure of ganglion cells to descend into myenteric and submucosal plexuses

Complication - if dilates too much, rupture

Treatment - resection of involved bowel

Question 2

<p>
On inspection of a colon biopsy, you see exudative plaques on the mucosa that are raised and yellow - some might say pseudomembranous. What do you have a suspicion is in the recent medical history of this colon's owner?</p>

Answer 2

<p>
Antibiotic use, mainly of Clindamycin. Usually due to Clostridium difficile, which produces toxins that damage the colonic mucosa - pseudomembrane consists of fibrin, mucin, and inflammatory cells</p>

Question 3

What are two potential etiologies of diverticula in the colon?

Answer 3

1) Increased intraluminal pressure - low fiber diets
2) Defects in wall of colon - increased age, interruption of layers by vasculature

Either of these two components can lead to an acquired herniation of the mucosa and submucosa through the muscularis propria

Question 4

What are potential complications of diverticula in the colon?

Answer 4

A) diverticulitis - retained fecal material, causing inflammation and abscess formation

B) Rectal bleeding

C) Fistula formation with surrounding organs, including the bladder, vagina, small intestine, and skin

Question 5

20 yo female presents with recurrent bouts of bloody diarrhea and abdominal pain. Upon biopsy, you see pseudopolyps and loss of haustra with crypt absesses full of neutrophils. There are mucosal and submucosal ulcers. Her disease seems to only involve the rectum and descending colon. Dx?

Answer 5

Ulcerative colitis

Question 6

20 yo female presents with recurrent bouts of bloody diarrhea and abdominal pain. Upon biopsy, you see a cobblestone mucosa, streaking fat, and strictures. The inflammation extends through the full thickness of wall and appears as knife-like fissures. Her disease seems to be spotty but mostly in the terminal ileum. Dx?

Answer 6

Crohn disease

Question 7

Describe the molecular progression of the adenoma-carcinoma sequence

Answer 7

1) APC mutation (chromosome 5) increases risk for formation of polyp. Tumor suppressor, so need both copies knocked out to progress. Familial Adenomatous Polyposis is an inherited mutation of APC.
2) K-ras mutation, leads to formation of polyp
3) p53 mutation and increased expression of COX allow for progression to carcinoma (aspirin is protective)

Question 8

What are the extraintestinal manifestations of ulcerative colitis?

Answer 8

arthritis (most common), uveitis, erythema nodosum, pyoderma gangrenosum, sclerosing cholangitis, deep vein thromboses

Question 9

62 yo man with a history of coronary artery disease presents with severe crampy abdominal pain and blood in his stool. Abdominal sounds are absent. If this is an ischemic injury, what artery has most likely been occluded? What areas of the small intestine and colon are most vulnerable to ischemic injury?

Answer 9

• most likely superior mesenteric artery

- watershed areas are at great risk - splenic flexure, rectosigmoid area

Question 10

What are the most common intestinal complications of Crohn disease?

Answer 10

intestinal obstruction and fistulas