Path 48: GI - Small Intestine and Large Intestine (Non-Neoplastic)

Created by lcoghill 

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Meckel's Diverticulum

incomplete involution of vitelline duct -> rule of 2s -> 2% of normal population, within 2 feet of Ileocecal valve, average length is 2 inches -> on anti-mesenteric border, all layers of GIT (true diverticulum) -> sometimes lined by gastric mucosa or pancreatic tissue

Meckel's clinical

commonly asymptomatic, complications: hemorrhage and peptic ulceration, intestinal obstruction, diverticulitis, perforation, fistula

Malabsorption syndrome

defective absorption of fats, fat soluble and other vitamins, proteins, carbohydrates, electrolytes, minerals and water -> clinically present with chronic diarrhea -> typically fatty feces (steatorrhea) -> impaired digestion, absorption, delivery

Celiac disease (gluten sensitive enteropathy)

common in whites 1-10 years (typically genetically sensitive to gluten), changes more marked in proximal part of intestine (marked atrophy and loss of villi -> reduced area for absorption, increased intraepithelial lymphocytes, elongated and hyperplastic crypts, increased number of lymphocytes, plasma cells in lamina propria) -> reversal of changes after gluten free diet

Pathogenesis of celiac disease

HLA-B8, HLA-DR3-DQw2 mutations -> adenovirus and gluten -> causes immunologic response -> patients almost always express MHC class II antigens HLA-DQ2, HLA-DQ8

Diagnosis of celiac disease

documentation of malabsorption (iron deficiency anemia), small intestine biopsy, reversal of changes after gluten free diet, serologic tests (anti-gliadin and anti-endomysial antibodies, anti-tissue transglutaminase tTG antibodies -> best test but may be false negative without serum IgA levels), long term risk of intestinal lymphomas (T cell type)

Tropical sprue (post infectious sprue)

in people living or visiting tropics (pay attention to history) -> symptoms appear months or years later -> pathogenesis is related to bacterial infection superimposed on pre-existing small intestine injury -> all parts of SI are involved equally -> difficult to differentiate from celiac disease -> responds to antibiotics

Whipple's Disease

Systemic disease involving mainly intestine, joints and CNS -> caused by gram positive sickle shaped actinomycetes- Trepophyrema whippelii -> more common in males (10:1), mucosa laden with distended macrophages (villi loaded with foamy macrophages) in lamina propria contain PAS positive granules -> rod shaped bacilli can be seen on EM -> treat with antibiotics

Hirschsprung's Disease (Congenital megacolon)

most common cause of congenital intestinal obstruction -> males more common (4:1), in 10% of Down syndrome patients -> absence of ganglion cells in Meissner's and Auerbach's plexus (defect in migration and survival of neuroblasts) -> rectum is always affected -> dilation and hypertrophy proximal to aganglionic segment -> delayed meconium, constipation, abdominal distension, diagnosed by rectal biopsy (rat tail pattern on barium X ray); complications: enterocolitis, perforation and peritonitis

Diverticular disease (diverticulosis and diverticulitis -> not true diverticuli)

common in western world, 50% in older than 60 years -> flask like structures (95% sigmoid colon) extending from lumen through muscular layer -> lack of dietary fiber leads to sustained bowel contractions and increased intraluminal pressure -> herniation of colonic wall at sites of focal defects

Diverticulosis

usually asymptomatic but sometimes painless bleeding

Diverticulitis

lower abdominal pain, constipation, diarrhea, flatulence, fever -> can lead to perforation

Colitis

caused by infections (bacterial, viral, protozoal - amebic), necrotizing enterocolitis, antibiotic associated (pseudomembranous), ischemic, idiopathic inflammatory bowel disease (IBS) -> causes diarrhea (mucoid/bloody), abdominal pain (usually below umbilicus), abdominal cramps, tenesmus (painful defecation)

Pseudomembranous colitis (C. difficile)

associated with broad spectrum antibiotic use -> toxin mediated damage -> rectosigmoid colon exhibits raised yellow plaques -> fibrinopurulent necrotic debris (pseudomembranes -> surface epithelium denuded, superficially damaged crypts distended by mucopurulent exudate which erupts to form a mushrooming cloud -> coalescence of these clouds leads to pseudomembrane formation)

Amebic colitis (entamoeba histolytica)

fecal oral route, may resemble IBD, gradual dysentery caused by parasite, chronic destructive colitis with flask shaped ulcers with organisms engulfing red cells -> treat with anti-parasitics

Ulcerative lesions of the intestines

IBS (includes Crohn and ulcerative colitis), peptic ulcers (duodenal), infectious etiology (bacterial - salmonella, TB, CMV in immunosuppressed), ischemic colitis, drugs (NSAIDs - stricture formation is common), tumors

Ulcerative colitis

intermittent rectal bleeding, bloody diarrhea and abdominal pain -> typically continuous colonic involvement

Crohn disease

more variable symptoms than UC that include abdominal pain, fatigue, weight loss and fever -> typically patchy transmural involvement

TB

Langhan's type giant cells, chronic abdominal pain, multifocal involvement (jejunum to ileum, TI most common) -> anular circular or oval ulcers, lying transversely -> single ulcers are large, multiple ulcers smaller -> granulomatous inflammation, often necrotizing

Typhoid

fever, headache, abdominal pain, rash, diarrhea -> longitudinal ulcers, typically over Peyer patches

Idiopathic inflammatory bowel disease

includes Crohn's disease and ulcerative colitis -> chronic relapsing inflammatory disorders of obscure origin ->

Ulcerative colitis

non-granulomatous inflammation limited to colon -> intense lamina infiltrate -> pseudopolyp formation -> affects mucosa and submucosa -> extends in continuous fashion -> starts in rectum, more common in whites 20-25, associated with primary sclerosing cholangitis (PSC) -> HLA-DRB1 association

Ulcerative colitis

10% of cases back wash ileitis, serosa usually normal, mucosa red granular and friable, broad based ulcers, isolated islands of regenerating mucosa bulge in between to create pseudopolyps

Crohn's disease (terminal ileitis, regional ileitis, granulomatous colitis)

granulomatous inflammation that can affect any part of GIT from mouth to anus -> common in US, females more than males, common in Jews -> sharply delimited and transmural involvement by an inflammatory process -> presence of non caseating granulomas -> mucosal fissuring with formation of fistulas

Crohn's disease

small intestine alone 30%, small intestine and colon 40%, colon alone 30% -> creeping up of mesenteric fat because of fibrosis -> mesentery is thickened and fibrotic -> wall is thickened (because of edema, hypertrophy, fibrosis and inflammation) -> long narrow thickened segments of small intestine (radiographically - string sign) -> cobble-stoning of mucosa

Clinical features of IBD

relapsing disorder, attacks of bloody mucoid diarrhea, lower abdominal pain, abdominal cramps, tenesmus -> flare ups with physical and mental stress, fever and weight loss in severe cases, features of malabsorption -> small intestine has features of subacute intestinal obstruction

Extra intestinal manifestations of IBD

seen in both CD and UC (More common in UC) -> can develop even before GI symptoms -> migratory polyarthritis, sacroileitis, ankylosing spondylitis, erythema nodosum, clubbing of finger tips, sclerosing cholangitis -> increased risk of developing malignancy

Ischemic bowel disease

common in elderly, mild features in only mucosal involvement (nausea, vomiting and bloody stools), transmural involvement (severe abdominal pain and tenderness, gangrene, perforation, peritonitis, shock and vascular collapse, mortality high - 50-75%) -> venous vs. arterial insufficiency -> occlusive (arterial thrombosis, arterial embolism, venous thrombosis) or non-occlusive (cardiac failure, shock, dehydration) or miscellaneous (radiation, volvulus, herniation)

Chronic ischemic colitis

insidious, chronic inflammation and fibrosis, stricture formation, common at water shed areas (splenic flexure most common) -> intermittent attacks of pain (intestinal angina) -> can mimic inflammatory bowel disease

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