Gastrointestinal Quiz: Ischemic Colitis and IBS

Ischemic Colitis

• Occurs when there is ischemic damage to the colon, typically at the splenic flexure (watershed area of the superior mesenteric artery [SMA])
• Atherosclerosis of SMA is the primary cause of ischemic colitis
• Presents with postprandial pain and weight loss, which can progress to infarction characterized by pain and bloody diarrhea

Irritable Bowel Syndrome

• Characterized by relapsing abdominal pain with bloating, flatulence, and changes in bowel habits (diarrhea or constipation)
• Symptoms typically improve with defecation, and are commonly seen in middle-aged females
• No identifiable pathologic changes are seen in irritable bowel syndrome
• Disturbed intestinal motility is thought to contribute to the development of irritable bowel syndrome
• Increasing dietary fiber may help alleviate symptoms

Colonic Polyps

• Raised protrusions of the colonic mucosa, with hyperplastic and adenomatous polyps being the most common types
• Hyperplastic polyps: due to hyperplasia of glands, classically show a serrated appearance on microscopy
  • Most common type, usually arise in the left colon (rectosigmoid)
  • Benign, with no malignant potential
• Adenomatous polyps: due to neoplastic proliferation of glands
  • Second most common type
  • Benign, but premalignant, may progress to adenocarcinoma through the adenoma-carcinoma sequence
• Adenoma-carcinoma sequence: describes the molecular progression from normal colonic mucosa to adenomatous polyp to carcinoma
  • APC mutations (sporadic or germline) increase the risk for the formation of polyp
  • K-ras mutation leads to the formation of polyp
  • p53 mutation and increased expression of COX allow for progression to carcinoma; aspirin impedes progression from adenoma to carcinoma

Screening and Removal

• Performed by colonoscopy and testing for fecal occult blood
• Goal is to remove adenomatous polyps before progression to carcinoma
• Polyps are usually clinically silent, but can bleed
• All polyps are removed and examined microscopically during colonoscopy
• Greatest risk for progression from adenoma to carcinoma is related to size greater than 2 cm, sessile growth, and villous histology

Familial Adenomatous Polyposis (FAP)

• Autosomal dominant disorder characterized by 100s to 1000s of adenomatous colonic polyps
• Due to inherited APC mutation (chromosome 5), increases propensity to develop adenomatous polyps throughout colon and rectum
• Colon and rectum are removed prophylactically; otherwise, almost all patients develop carcinoma by 40 years of age

Associated Syndromes

• Gardner syndrome: FAP with fibromatosis and osteomas
  • Fibromatosis: non-neoplastic proliferation of fibroblasts, arises in retroperitoneum (desmoid) and locally destroys tissue
  • Osteoma: benign tumor of bone that usually arises in the skull
• Turcot syndrome: FAP with CNS tumors (medulloblastoma and glial tumors)