Pathoma Small Bowel

Question 1

duodenal atresia

Answer 1

*congenital failure of small bowel to canalize
*associated with Down syndrome
*clinical features:
-polyhydramnios
-distension of stomach and blind loop of duodenum (“double-bubble” sign)
-bilious vomiting

Question 2

Meckel Diverticulum

Answer 2

*outpouching of all 3 layers of bowel wall (TRUE diverticulum)
*arises due to failure of vitelline duct to involute

*Rules of 2’s:
-seen in 2% of the population (most common congenital anomaly in GI tract)
-2 inches long and located in the small bowel within 2 ft of the ileocecal valve
-can present during the first 2 years of life with bleeding (due to heterotopic gastric mucosa), volvulus, intussusception, or obstruction (mimics appendicitis); however, most cases are asymptomatic

Question 3

volvulus

Answer 3

*twisting of bowel along its mesentery
*results in obstruction & disruption of blood supply (infarction)
*most common locations are sigmoid colon (elderly) and cecum (young adults)

Question 4

small bowel infarction

Answer 4

*small bowel is highly susceptible to ischemic injury
-transmural infarction occurs with embolism/thrombosis of SMA or thrombosis of mesenteric vein
-mucosal infarction occurs with marked hypotension
*clinical features: abdominal pain, bloody diarrhea, decreased bowel sounds

Question 4

intussusception

Answer 4

*telescoping of proximal segment of bowel into distal segment:
-telescoped segment is pulled forward by peristalsis, resulting in obstruction and disruption of blood supply with infarction

*associated with a leading edge (focus of traction):
-in children: most common cause = lymphoid hyperplasia (terminal ileum to cecum)
-in adults: most common cause = tumor

Question 5

lactose intolerance

Answer 5

*decreased function of the lactase enzyme found in the brush border of enterocytes
*presents with: abdominal distension and diarrhea upon consumption of milk products; undigested lactose is osmotically active
*deficiency may be congenital or acquired; temporary deficiency is seen after small bowel infection

Question 6

celiac disease - pathogenesis

Answer 6

*immune-mediated damage of small bowel villi due to gluten exposure
*associated with HLA DQ2 and DQ8
*pathogenic component of gluten = GLIADIN
*gliadin is DEAMIDATED by tTG
*deamidated gliadin is presented by APCs via MHC II
*helper T cells mediate tissue damage

Question 7

celiac disease - lab findings

Answer 7

*IgA antibodies against endomysium, tTG, or gliadin (IgG antibodies useful if IgA deficient)
*duodenal biopsy reveals flattening of villi, hyperplasia of crypts, and increased intraepithelial lymphocytes
*damage most prominent in duodenum (jejunum and ileum are less involved)

Question 8

celiac disease - clinical presentation

Answer 8

*children: abdominal distension, diarrhea, and failure to thrive
*adults: chronic diarrhea & bloating
*small, herpes-like vesicles may arise on skin (dermatitis herpetiformis); due to IgA deposition at tips of dermal papillae; resolves with gluten free diet
*all symptoms resolve with gluten free diet (small bowel carcinoma and T-cell lymphoma present with refractory disease, despite good dietary control)

Question 9

tropical sprue

Answer 9

*damage to small bowel villi due to an unknown organism resulting in malabsorption
*similar to celiac disease, except:
-occurs in tropical regions
-arises after infectious diarrhea and responds to antibiotics
-damage is most prominent in jejunum & ileum (contrast to celiac, where duodenum most involved)
-secondary B12 or folate deficiency may ensue

Question 10

Whipple disease

Answer 10

*systemic tissue damage characterized by macrophages loaded with Tropheryma whippelii organisms
*partially destroyed organisms are present in macrophage lysosomes (positive for PAS)
*classic site of involvement = small bowel lamina propria
-results in fat malabsorption & steatorrhea (because macrophages compress lacteals)
*other common sites of involvement include synovium of joints, cardiac valves, lymph nodes, and CNS

Question 11

abetalipoproteinemia

Answer 11

*autosomal recessive deficiency of apolipoprotein B-48 and B-100
*clinical features:
-malabsorption (due to defective chylomicron formation - requires apo B-48)
-absent plasma VLDL and LDL (require apo B-100)

Question 12

carcinoid tumor

Answer 12

*malignant proliferation of neuroendocrine cells; low-grade malignancy [tumor cells contain neurosecretory granules that are positive from CHROMOGRANIN]
*can arise anywhere in the gut; small bowel is most common site [grows as a submucosal polyp-like nodule]
*often secretes SEROTONIN (broken down in the liver by MAO into 5-HIAA, which is excreted in the urine)
*METASTASIS of carcinoid tumor to the liver allows serotonin to bypass liver metabolism (results in carcinoid syndrome and carcinoid heart disease)

Question 13

carcinoid syndrome

Answer 13

*only occurs once the carcinoid tumor metastasizes to the liver
*characterized by bronchospasm, diarrhea, and flushing of skin
*sx can be trigged by alcohol or emotional stress
*carcinoid heart disease = R-sided valvular fibrosis (deposition of collagen in valves); leads to tricuspid regurgitation and pulmonary valve stenosis