VIVA: Pathology - Gastrointestinal Flashcards
Describe the common causes of bowel obstruction
4/7 to pass:
- Adhesions
- Hernia
- Malignancy
- Volvulus
- Intussusception
- Mesenteric infarct
- Strictures (e.g. due to Crohn’s, radiation, mesenteric ischaemia)
How does a hernia form, and cause a bowel obstruction?
- Weakness/defect in abdominal wall* leading to protrusion of serosa-lined pouch of peritoneum (hernial sac)
- Visceral protrusion* (small bowel, large bowel, or omentum most often involved)
- Entrapment of hernia sac in a narrow neck* causes pain
- Persistent obstruction leads to venous stasis and oedema, which can cause incarceration and strangulation
- Common locations include inguinal, femoral, incisional and umbilical
*needed to pass + 2 others
Describe some important clinical sequelae of bowel obstruction
- Intestinal perforation *
- Intestinal ischaemia *
- Peritonitis
- Sepsis
- Abscess
- Electrolyte disturbance
- Vomiting and aspiration
- Death
*needed to pass
Which bacterial class does Escherichia coli belong to?
E. coli is a Gram negative bacillus which is a facultative anaerobe; it is also a normal GI commensal
What is the difference between an endotoxin and an exotoxin?
Endotoxins:
- Lipopolysaccharides in the outer membrane of the cell wall of Gram negative bacteria which cause injury via the host immune response
Exotoxins:
- Proteins that are secreted by the bacterium and cause direct injury
List some types of infections that can be commonly caused by E. coli
3 to pass:
- UTI
- Prostatitis
- Epididymo-orchitis
- Infectious enterocolitis
- Cholecystitis
- Bacterial peritonitis
What are the infectious causes of gastroenteritis? Give examples
- Viral*:
- Norovirus
- Rotavirus
- Adenovirus - Bacterial*:
- Cholera
- Campylobacter
- Shigella
- Salmonella
- Enteric typhoid fever
- Yersinia
- E. coli
- C. difficile - Parasitic*:
- Ascaris
- Strongyloides
- Necator
- Ancylostoma
- Trichuris
- Enterobius
- Schistosomiasis
- Intestinal cestodes
- Entamoeba
- Giardia
- Cryptosporidium - Mycobacterial*
*2/4 categories with 1 example from each to pass
What are non-infectious causes of enterocolitis?
2 to pass:
- Cystic fibrosis
- Coeliac disease
- Autoimmune enteropathy
- Inflammatory bowel disease
- Irritable bowel syndrome
- Ischaemic gut
- Diverticulitis
- Lactase (disaccharidase) deficiency / lactose intolerance
- Environmental enteric dysfunction
Describe the classification of major categories of diarrhoea
- Secretory*:
- Isotonic stool
- Persists during fasting
- E.g. cholera - Osmotic*:
- Excessive osmotic force exerted by unabsorbed luminal solutes
- Abates with fasting
- E.g. sorbitol - Malabsorptive*:
- Generalised failure of nutrient absorption associated with steatorrhoea
- Abates with fasting
- E.g. chronic pancreatitis - Exudative*:
- Secondary to inflammatory disease
- Characterised by purulent, often bloody stools
- Persists during fasting
- E.g. IBD
*2/4 to pass
What is pseudomembranous colitis?
- Colitis caused by overgrowth of C. difficile* (can also be caused by Salmonella, C. perfringens type A, Staph aureus)
- Associated with antibiotic use
- Forms a pseudomembrane* made up of adherent layer of inflammatory cells and debris
*needed to pass
What are the risk factors for development of pseudomembranous colitis?
2/3 to pass:
- Advanced age
- Hospitalisation
- Antibiotic treatment
What are the clinical features of pseudomembranous colitis?
- 30% of hospitalised patients colonised, but most asymptomatic
- Fever *, leucocytosis, abdominal pain *, cramps, hypoalbuminaemia, watery diarrhoea *, dehydration, rarely gross bloody diarrhoea
- Diagnosis usually via detection of toxin
- Treated with metronidazole, vancomycin
*needed to pass
What conditions can lead to infarction of the bowel?
- Acute arterial obstruction*:
- Atherosclerosis
- Aortic aneurysm
- Hypercoaguable state
- OCP use
- Embolism - Intestinal hypoperfusion*:
- Cardiac failure
- Shock
- Dehydration
- Vasoactive drugs - Systemic vasculitis:
- Henoch Schonlein purpura
- Wegener’s granulomatosis - Mesenteric venous thrombosis:
- Hypercoaguable state
- Invasive neoplasm
- Cirrhosis
- Trauma
- Abdominal masses - Miscellaneous:
- Radiation
- Volvulus
- Stricture
- Amyloid
- Diabetes
*2 from each to pass + 2 total from other categories
What are the clinical features of ischaemic bowel?
- Severe pain* (may be transient)
- Tenderness
- Peritonism
- Nausea and vomiting
- Bloody diarrhoea
- Melaena
- Shock
- Hyper/hypothermia
- Sepsis
- needed to pass + 3 others
What parts of the bowel are most susceptible to ischaemic injury and why?
- Watershed zones*:
- Splenic flexure, sigmoid colon, rectum
- Located at end of arterial supply - Surface epithelium:
- Villi more at risk than crypts (intestinal capillaries run from crypts up villi to surface)
*needed to pass + explanation
