Inflammatory bowel disease Flashcards
What is the primary function of the large intestine?
- Removes water from all indigestible gut contents
- Turns chyme into a semi-solid
What are the other functions of the large intestine?
- Production of certain vitamins
- Microbiome contains lots of commensal bacteria
- Acts as temporary storage until defecation
Where does the colonic mucosa get the majority of its nutrients from?
- Not from blood
- Short chain fatty acids derived from fermentation of dietary fibre
- The by-products of this fermentation include CO2, methane and hydrogen gas
Outline the relationship of the large intestine with the peritoneum
- Ascending and descending colon are retro-peritoneal
- Transverse colon and sigmoid colon have their own mesenteries
Outline the relationship of the rectum with the peritoneum
- Upper 1/3 is intra-peritoneal
- Middle 1/3 is retroperitoneal
- Lower 1/3 has no peritoneum
Outline the arterial supply of the mid-gut
- Supplied by branches of superior mesenteric artery
- Ileo-colic branch supplies caecum (small intestine)
- Right colic branch supplies ascending colon
- Middle colic branch supplies transverse colon
Outline the arterial supply of the hindgut
- Supplied by branches of inferior mesenteric artery
- Left colic branch supplies descending colon
- Sigmoid branch supplies descending colon and sigmoid colon
- Superior rectal artery supplies upper 1/3 of rectum
Outline the venous drainage of the midgut
- Drains into superior mesenteric vein
Outline the venous drainage of the hindgut
- Drains into inferior mesenteric vein
Outline the venous drainage of the rectum
- Upper 1/3 drains into superior rectal vein (IMV)
- Middle and lower 1/3s drain into systemic venous system
- This is a site of portosystemic anastomosis (i.e. varices can occur here)
Compare the structure of the large intestine with the structure of the small intestine
- Large intestine is much shorter
- Large intestine is much wider
- Has crypts, not villi
Describe the muscular walls of the large intestine
- External longitudinal muscle is incomplete
- Instead it is divided into 3 distinct bands called taeniae coli
- Haustra are sacculations caused by contraction of taeniae coli
Give an overview of water absorption in the large intestine
- Facilitated by ENac channels (like in DCT)
- Induced by aldosterone
- <100mls water excreted in faeces each day bu 1500mls enter colon each day
- Most absorption in proximal colon
- Much tighter tight junctions allows a bigger gradient to form and means there’s less back diffusion of ions
What is the broad definition for inflammatory bowel disease?
- Group of conditions characterised by idiopathic inflammation of the GI tract
What are the 2 common types of IBD?
- Crohn’s disease
- Ulcerative colitis
Give an overview of Crohn’s disease
- Affects anywhere in GI tract from mouth to anus
- Ileum involved in most cases
- Transmural
- Skip lesions (areas in between affected areas of bowel)
Give an overview of Ulcerative colitis
- Begins in rectum
- Can extend to involve entire colon
- Continuous pattern
- Mucosal inflammation (superficial)
What other issues are associated with IBD?
- MSK pain e.g. arthritis
- Skin e.g. erythema nodosum, pyoderma gangrenosum, psoriasis
- Liver/biliary tree e.g. primary sclerosing cholangitis
- Eye problems
What are the causes of IBD?
- Genetic
- Gut organisms (altered interaction)
- Immune response
- Antibiotics
- Infections
- Smoking (though this slightly suppresses UC)
- Diet
What might you see in a classic presentation of Crohn’s disease?
- Multiple loose stools per day
- Not bloody
- Weight loss
- Right lower quadrant pain
- Maybe joint pains
- Tender mass due to scarring
- Mild perianal inflammation/ulceration
- Low grade fever
- Mild anaemia
What pathology does Crohn’s disease cause?
- Skip lesions
- Hyperaemia
- Mucosal oedema
- Discrete superficial ulcers
- Deeper ulcers
- Transmural inflammation
- Thickening of bowel wall
- Narrowing of lumen
- Cobblestone appearance
- Fistulae
What causes the cobblestone appearance seen in Crohn’s disease?
- Inflamed oedematous tissue in between linear ulcers
What are fistulae?
- Abnormal connections between 2 epithelium lined surfaces
- In Crohn’s can be bowel-bowel/bladder/vagina/skin
What microscopic details would you see in Crohn’s disease?
- Granuloma formation
- Organised collection of epithelioid macrophages
How would we investigate Crohn’s disease?
- Bloods - check for anaemia
- CT/MRI scans - check for bowel wall thickening, obstruction, extramural problems
- Barium enema/follow through - identify strictures
What would be seen on a colonoscopy in someone with Crohn’s?
- Gross pathological changes
- Skip lesions
- Cobblestone appearance
- Fistulae
- Strictures
- Less blood than in ulcerative colitis
What might you see in a typical presentation of ulcerative colitis?
- Multiple bloody stools per day
- Mucus in stools
- Weight loss
- Mild lower abdominal pain/cramping
- Mildly tender abdomen
- No perianal diseases
- Normal temperature
What microscopic changes can be seen in histology of ulcerative colitis?
- Chronic inflammatory infiltrate of lamina propria
- Crypt abscesses (neutrophilic exudate in crypts)
- Crypt distortion
- Irregular shaped glands with dysplasia
- Dark crowded nuclei
- Reduced numbers of goblet cells
What pathological changes occur in ulcerative colitis?
- Pseudopolyps can develop after repeated episodes of inflammation then healing
- Non-neoplastic
- Loss of haustra due to inflammation
How do we investigate ulcerative colitis?
- Bloods - anaemia, serum markers
- Stool cultures
- Colonoscopy
- Plain abdominal radiographs
- Barium enema (mild cases only)
- CT/MRI (less useful in diagnosing uncomplicated UC)
What is indeterminate colitis?
- Even after diagnostic evaluation, there are disorders that cannot be classified
- Occurs in 10% of cases
Outline the distinguishing characteristics of Crohn’s vs UC
- Crohn’s disease occurs anywhere in GI tract, UC only in rectum/colon
- Only UC involves rectum
- 25% patients have gross bleeding in Crohn’s, 75% in UC
- 75% patients have perianal disease in Crohn’s, this is rare in UC
- Fistula formation in Crohn’s only
- Potential for malnutrition in Crohn’s only
Outline the pathological features of Crohn’s vs UC
- Transmural inflammation occurs in Crohn’s but is rare in UC
- Granulomas seen in 75% of Crohn’s cases but not in UC
- Fibrosis common in Crohn’s only
- Crypt abscesses common in UC but rare in Crohn’s
Outline the endoscopic changes in Crohn’s vs UC
- Skip lesions in Crohn’s but continuous mucosal involvement in UC
- Aphthous ulcers common in Crohn’s but rare in UC
- Linear ulcers common in Crohn’s but rare in UC
- Friable mucosa common in UC but rare in Crohn’s
- Cobblestone appearance seen in severe cases of Crohn’s but not at all in UC
- Fistula common in Crohn’s but not seen in UC
- Narrowing common in Crohn’s but rare in UC
What can be seen in radiology of Crohn’s disease?
- On barium follow through can sometimes see long strictures
- String sign of kantour
What are the radiological features of UC?
- Double contrast enema
- Featureless descending and sigmoid colon
- Lacking haustral markings
- Lead pipe colon
- Continuous lesions without skipping
- Whole colon
- Mucosal inflammation
- Causes granular appearance
What are the treatment options for IBD?
- Aminosalicylates (sulfasalazine) - for flares and remission
- Corticosteroids (prednisolone) - fore flares only
- Immunomodulators (azathioprine) for fistulas/maintenance of remission
- Faecal transplants help with UC
What are the surgical treatments for Crohn’s disease?
- Not curative
- Strictures/fistulas
- As little bowel removed as possible
- Small intestine can’t be too short otherwise pt ends up with permanent diarrhoea
- Every time you do surgery, you risk causing adhesions
What are the surgical treatments for ulcerative colitis?
- Curable (colectomy) - entire colon removed and ileum connected directly to rectum
- Carried out if inflammation is not settling/there are precancerous changes/toxic megacolon
