Colon Flashcards
Hirschsprung Disease
defective relaxation and peristalsis of rectum and distal sigmoid colon due to failure of ganglion cells to descend into myenteric and submucosal plexus and is associated with Down syndrome
- myenteric plexus: regulates motility
- submucosal plexus: regulates blood flow, secretions and absorption
- causes obstruction (failure to pass meconium, empty rectal vault, dilatation of bowel proximal to obstruction with risk for rupture)
- rectal suction biopsy–> lack of ganglion cells
Colonic Diverticula
outpouchings of mucosa and submucosa through muscularis propria and is related to wall stress (constipation, straining, low-fiber) and arises when vasa recta traverse the muscularis propria (weak point)
- sigmoid colon= common area
- complications: rectal bleeding, diverticulitis, fistula
Angiodysplasia
malformation of mucosal and submucosal capillary beds arising in the cecum and right colon from high wall tension
*rupture presents as hematochezia
Hereditary Hemorrhagic Telangiesctasia
thin-walled BVs in mouth and GI
*rupture presents as bleeding
Ischemic Colitis
ischemic damage to the colon at the splenic flexure (watershed area of SMA) presenting with postprandial pain and weight loss (infarction results in pain and bloody diarrhea)
*atherosclerosis of SMA is the most common site
Irritable Bowel Syndrome
relapsing abdominal pain with bloating, flatulence and change in bowel habits that improves after defecating and is related to disturbed intestinal motility
*usually in middle-aged women
Colonic Polyps
raised protrusions of colonic mucosa- screen by colonoscopoy or fectal occult blood (remove before they become carcinoma)
*greatest risk for progression from adenoma to carcinoma is related to size >2cm, sessile growth and villous histolgy
<b>hyperplastic polyps</b>: hyperplasia of glands showing serrated appearance arising in Left colon and are benign
<b>adenomatous polyps</b>: neoplastic proliferation of glands that are premalignant and can progress to adenocarcinoma via adenoma-carcinoma sequence
Familial Adenomatous Polyposis
100s to 1000s of adenomatous colonic polyps from an inherited APC mutation
*colon and rectum are removed prophylactically otherwise the probability of developing carcinoma is high
<b>Gardner Syndrome</b>: FAP with fibromatosis (non-neoplastic proliferation of fibroblasts arising in retroperitoneum and locally destroys tissue) and osteomas (benign tumor of the bone)
<b>Turcot Syndrome</b>: FAP with CNS tumors (medulloblastoma and glial tumors)
Juvenile Polyp
hamartomatous (benign) polyp in children
Peutz-Jeghers Syndrome
hamartomatous (benign) polyps through GI tract and mucocutaneous hyperpigmentation on lips, oral mucosa and genital skin
*increased risk for colorectal, breast and gynecologic cancer
Colorectal Carcinoma
arises most commonly from adenoma-carcinoma sequence and a second important molecular pathway- microsatellite instability
Left sided: grows as a mapkin-ring lesion presenting as decreased stool caliber, left lower quadrant pain and blood-streaked stool
Right sided: raised lesion, presents with iron-deficiency anemia (occult bleeding) and vague pain
- increased risk for Streptococcus bovis endocarditis
- CEA: detects recurrence and treatment response
Adenoma-Carcinoma Sequence
molecular progression from normal colonic mucosa to adenomatous polyp to carcinoma
- APC mutations increased risk for formation of polyp
- K-ras mutation leads to formation of polyp
- p53 mutation and increased expression of COX allows for progression to carcinoma; aspirin impedes progression from adenoma to carcinoma
Microsatellite Instability
- microsatellites are repeating sequences of noncoding DNA- integrity of sequence (stability) is maintained during cell division
- instability indicates defective DNA copy mechanisms
- hereditary nonpolyposis colorectal carcinoma is due to inherited mutations in DNA mismatch repait enzymes (increased risk for colorectal, ovarian and endometrial carcinoma)–> colorectal carcinoma arises de novo at a relatively early age (usually right sided)
