Small bowel Flashcards
Duodenal atresia
Congenital failure of duodenum to canalize –> associated with Down syndrome
Clinical features
- polyhydramnios
- distension of stomach and blind loop of duodenum (“double bubble sign”
- bilious vomiting
Meckel diverticulum
Outpouching of all 3 layers of the bowel wall = true diverticulum –> arises due to the failure of the vitelline duct to involute
Rule of 2s
- seen in 2% of the population –> most common congenital anomaly of the GI tract
- 2 inches long and located in the small bowel within 2 feel 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
Volvulus
Twisting of bowel along its mesentery
- results in obstruction and disruption of the blood supply with infarction
- most common locations are sigmoid colon (elderly) and cecum (young adults)
Intussusception
Telescoping of proximal segment of bowel forward into distal segment
- telescoped segment is uplled forward by peristalsis, resulting in obstruction and disruption of blood supply with infarction –> results in currant jelly stools
- associated with a leading edge (focus of traction)
- in kids, the most common cause is lymphoid hyperplasia (e.g. due to rotavirus); usually arises in the terminal ileum, leading to intussusception into the cecum
- in adults, most common cause is tumor
Small bowel infarction
Small bowel is highly susceptible to ischemic injury
- transmural infarction –> occurs with thrombosis/embolism of the superior mesenteric artery or thrombosis of the mesenteric vein
- mucosal infarction –> occurs with marked hypotension
Clinical features
- abdominal pain
- bloody diarrhea
- decreased bowel sounds
Lactose intolerance
Decreased function of the lactase enzyme found in the brush border of enterocytes
- lactase normally breaks down lactose into glucose and galactose
- presents with abdominal distension and diarrhea upon consumption of milk products; undigested lactose is osmotically active
- deficiency may be congenital (rare autosomal recessive disorder) or acquired (often develops in late childhood) –> temporary deficiency is seen after small bowel infection (lactase is highly susceptible to injury)
Celiac disease
- pathophysiology
- clinical features
Immune mediated damage of small bowel villi due to gluten exposure
- associated with HLA-DQ2 + DQ8
Gluten is present in wheat and grains, its most pathogenic component is gliadin
- once absorbed, gliadin is deamidated by tissue transglutaminase
- deamidated gliadin is presented by antigen presenting cells via MHC class II
- helper T cells mediate tissue damage
Clinical presentation
- children classically present with abdominal distension, diarrhea, and failure to thrive
- adults classically present with chronic diarrhea and bloating
- small, herpes like vesicles may arise on the skin = dermatitis herpetiformis –> due to IgA deposition at the tips of dermal papillae; resolves with gluten free diet
Celiac disease
- lab findings
- treatment
- IgA antibodies against endomysium, tTG, or gliadin –> IgG antibodies are also present and are useful for diagnosis in individuals who have IgA deficiency (increased incidence of IgA deficiency is seen in celiac disease)
- duodenal biopsy reveals flattening of villi, hyperplasia of crypts, and increased intraepithelial lymphocytes
- damage is most prominent in the duodenum –> jejunum and ileum are less involved
Symptoms resolve with a gluten free diet
- small bowel carcinoma and T cell lymphoma are late complications that present as refractory disease despite good dietary control
Tropical sprue
Damage to small bowel villi due to an unknown organism resulting in malabsorption
Similar to celiac disease except…
- occurs in tropical regions (carribean)
- arises after infectious diarrhea and responds to antibiotics
- damage is most prominent in jejunum and ileum (secondary vit V12 or folate deficiency may ensure) –> duodenum less commonly involved
Whipple disease
Systemic tissue damage characterized by macrophages loaded with tropheryma whippeli organisms –> partially destroyed organisms are present in macrophage lysosomes (positive for PAS)
- classic site of involvement is the small bowel lamina propria
- macrophages compress lacteals –> chylomicrons cannot be transferred from enterocytes to lymphatics –> results in fat malabsorption and steatorrhea
- other common sites of involvement include synovium of joints (arthritis), cardiac valves, lymph nodes and CNS
Abetalipoproteinemia
Autosomal recessive deficiency of apolipoprotein B-48 and B-100
Clinical features
- malabsorption –> due to defective chylomicron formation (requires B-48)
- absent plasma VLDL and LDL –> requires B-100
Carcinoid tumor
Malignant proliferation of neurendocrine cells = low grade malignancy
- tumor cells contain neurosecretory granules that are positive for chromogranin
- can arise anywhere along the gut –> small bowel is the most common site
- grows as a submucosal polyp like nodule
- often secretes serotonin
- serotonin released into the portal circulation and metabolized by liver monoamine oxidase (MAO) into 5-HIAA –> excreted in the urine
Metastasis of carcinoid tumor to the liver allows serotonin to bypass liver metabolism
- serotonin is released into the hepatic vein and leaks into systemic circulation via hepato-systemic shunts, resulting in carcinoid syndrome and carcinoid heart disease
- carcinoid syndrome –> characterized by bronchospasm, diarrhea and flushing of skin; symptoms can be triggered by alcohol or emotional stress, which stimulates serotonin release from the tumor
- carcinoid heart disease –> characterized by right sided valvular fibrosis (increased collagen) leading to tricuspid regurg and pulmonary valve stenosis –> left sided valve lesions are not seen due to presents of MAO in the lung (metabolized serotoinin)
Acute appendicitis
Acute inflammation of the appendix –> most common cause of acute abdomen
- related to obstruction of the appendix by lymphoid hyperplasia (kids) or a fecalith (adults)
Clinical features
- periumbilical pain, fever and nausea –> pain eventually localizes to right lower quadrant = McBurney point
- rupture results in periotonitis that presents with guarding and rebound tenderness
- periappendiceal abscess is a common complication
