Colon Flashcards
Inflammatory Bowel Disease
Chronic, relapsing inflammation of bowel –> possibly due to abnormal immune response to enteric flora
Classically presents in young women as recurrent bouts of bloody diarrhea and abdominal pain
- more prevalent in the west, particularly in caucasians and eastern european jews
Dx of exclusion –> symtomps mimic other causes of bowel inflammation
Subclassified as ulcerative colitis or crohns disease
Hirschsprung disease
Defective relaxation and peristalsis of the rectum and distal sigmoid colon
- associated with down syndrome
- due to congenital failure of ganglion cells (neural crest-derived) to descend into myenteric and submucosal plexus
Clinical features are based on obstruction
- failure to pass meconium
- empty rectal vault on digital rectal exam
- massive dilation (megacolon) of bowel proximal to obstruction with risk for rupture
Rectal suction biopsy reveals lack of ganglion cells
Treatment involves resection of the involved bowel; ganglion cells are present in the bowel proximal to the diseased segment
Colonic diverticula
Outpouchings of mucosa and submucosa through the muscularis propria (false diverticulum)
Related to wall stress
- associated with constipation, straining and low fiber diet –> commonly seen in older adults (risk increases with age)
- arise where the basa recta traverse the muscularis propria (weak pointin the colonic wall) –> sigmoid colon is the most common location
Usually asymptomatic –> complications include:
- rectal bleeding (hematochezia = bright red blood in toilet)
- diverticulitis –> due to obstruction with fecal material; presents with appendicitis like symptoms in the left lower quadrant
- fistula –> inflamed diverticulum ruptures and attaches to a local structure
- –> colovesicular fistula = presents with air (or stool) in urine (goes to bladder)
Angiodysplasia
Acquired malformation of mucosal and submucosal capillary beds
- usually arises in the cecum and right colon due to high wall tension
- rupture classically presents as hematochezia in an older adult
Hereditary hemorrhagic telangiectasia
Autosomal dominant disorder resulting in thin walled blood vessels, especially in the mouth and GI tract
- rupture presents as bleeding
Ischemic colitis
Ischemic damage to the colon, usually at the splenic flexure (watershed area of SMA)
- atherosclerosis of SMA is the most common cause
- presents with post prandial pain and weight loss
- infarction results in pain and blood diarrhea (inflammatory)
Irritable bowel syndrome
Relapsing abdominal pain with bloating, flatulence, and change in bowel habits (diarrhea or constipation) that improves with defecation
- classically seen in middle aged females
- related to disturbed intestinal motility –> no identifiable pathologic changes
- increased dietary fiber may improve symptoms
Colonic polyps
Raised protrusions of colonic mucosa –> most common types are hyperplastic and adenomatous polyps
- hyperplastic polyps –> due to hyperplasia of glands; classically show a serrated appearance on microscopy
- –> most common type of poly; usually arise in the left colon (rectosigmoid)
- –> benign, with no malignant potential
- adenomatous polyps –> due to neoplastic proliferation of glands; second most common type of colonic polyp
- –> benign, but premalignant; may progress to adenocarcinoma via 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 risk for formation of poly
- Kras mutation leads to formation of polyp
- p53 mutation and increased expression of COX allow for progression to carcinoma –> aspirin impedes progression from adenoma to carcinoma
Greatest risk for progression from adenoma to carcinoma
- increased size (>2 cm)
- sessile growth
- villous histology
Familial adenomatous polyposis syndrome
Autosomal dominant disorder characterized by hundreds to thousands of adenomatous colonic polyps
- due to inherited APC mutation on 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 y.o
Gardner syndrome
Turcot syndrome
Gardner syndrome –> FAP with fibromatosis and osteomas
- fibromatosis –> non-neoplastic proliferation of fibroblasts; arises in retroperitoneum (desmoid) and locally destroys tissue
- osteoma –> bening tumor of bone that usually arises in the skull
Turcot syndrome –> FAP with CNS tumors (medulloblastomas + glial tumors)
Juvenile polyp
Sporadic, hamartomatous (benign) polyp that arises in children –> usually presents as a solitary rectal polyp that prolapses and bleeds
Juvenile polyposis –> characterized by multiple juvenile polyps in the stomach and colon
- large numbers of juvenile polyps increases the risk of progression to carcinoma
Peurtz-jeghers syndrome
Hamartomatous (benign) polyps throughout the GI tract and mucocutaneous hyperpigmentation (freckle-like spots) on lips, oral mucosa and genital skin
- autosomal dominant disorder
- increased risk for colorectal, breast and gynecologic cancer
Colorectal carcinoma
Carcinoma arising from colonic or rectal mucosa
- 3rd most common site of cancer and 3rd most common cause of cancer related death
- peak incidence 60-70 years of age
Most commonly arises from adenoma-carcinoma sequence (left side); a second important molecular pathway is microsatellite instability (right side)
- microsatellites are repeating sequences of non-coding DNA –< integrity of sequence is maintained during cell division
- instability indicates defective DNA copy mechanisms (DNA MMR enzymes)
HNPCC –> due to inherited mutations in DNA MMR enzymes
- increased risk for colorectal, ovarian and endometrial carcinoma
- colorectal carcinoma arises de novo (not from adenomatous polyps) at a relatively early age
- usually right sided
Colorectal carcinoma is associated with na increased risk for strep bovi endocarditis
