S7: IBD & distal tract pathology Flashcards
Describe the arterial supply of the large intestine
Midgut component – superior mesenteric artery
Ileocolic – caecum
Right colic – ascending colon
Middle colic – transverse colon
Hindgut component – inferior mesenteric artery
Left colic – descending colon
Sigmoid – descending colon
Superior rectal artery – upper 1/3 rectum
Describe the venous drainage of the large intestine
Midgut drains into the superior mesenteric vein
Hindgut drains into inferior mesenteric vein
Rectum:
Upper 1/3 drains into superior rectal vein
Middle and lower 1/3s drain into systemic venous system – site of portosystemic anastomosis
Describe the longitudinal muscle of the large intestine
External longitudinal muscle is incomplete:
- three distinct bands (teniae)
- haustra are sacculations cause by contraction of teniae coli
Describe water absorption in the colon
Facilitated by ENaC Similar to principle cells of the late distal convoluted tubule Most absorption in proximal colon Much tighter tight junctions: -allows bigger gradient to form -less back diffusion of ions
Define inflammatory bowel disease
Group of conditions characterised by idiopathic inflammation of the GI tract
Affect function of the gut
Describe Crohn’s disease
Affects anywhere in GI tract, but ileum involved in most cases
Transmural – affects whole gut wall
Skip lesions
Describe ulcerative colitis
Begins in rectum & can extend to involve entire colon
Continuous pattern
Mucosal inflammation
Describe other symptoms which are common with inflammatory bowel disease
MSK pain – arthritis
Skin – erythema nodosum, pyoderma gangrenosum, psoriasis
Liver/biliary tree – primary sclerosing cholangitis
Eye problems
Describe macroscopic and microscopic features of Crohn’s disease
Macroscopic – skip lesions, hyperaemia, mucosal oedema, discrete superficial ulcers, deeper ulcers, transmural inflammation, fistulae & cobblestone appearance
Microscopic – granuloma formation (if this is found – definite diagnosis is Crohn’s)
Describe investigations for Crohn’s
Bloods – anaemia
CT/MRI – bowel wall thickening, obstruction & extramural problems
Barium enema/follow through – used less now
Colonoscopy – gross pathological changes can be seen
Describe pathological changes which occur in UC
Chronic inflammatory infiltrate of lamina propria
Crypt abscesses (neutrophilic exudate in crypts)
Crypt distortion – irregular shaped glands with dysplasia, darker crowded nuclei
Reduced number of goblet cells
Pseudopolyps can develop after repeated episodes
Loss of haustra
Describe investigations for UC
Bloods – anaemia & serum markers Stool cultures Colonoscopy Plain abdominal radiographs Barium enema CT/MRI – less useful for diagnosing uncomplicated UC
What is indeterminate colitis?
Even after diagnostic evaluation, 10% have disorders that cannot be classified
Describe radiological features of Crohn’s
Barium follow through – sometimes see long strictures
String sign of kantour
Describe radiological features of UC
Featureless descending and sigmoid colon – lacking haustral markings & lead pipe colon
Continuous lesions without skipping
Whole colon
Mucosal inflammation – causes granular appearance
Describe surgical treatment for inflammatory bowel disease
Crohn’s – not curative, strictures/fistulas, as little bowel removed as possible
UC – curable (colectomy) -> inflammation not settling, precancerous changes & toxic megacolon
Describe the presentation of Crohn’s
Multiple non-bloody loose stools/day Weight loss Right lower quadrant pain 15-30 year old Smoking makes it worse
Describe the presentation of UC
Multiple bloody stools/day
Middle abdominal pain
20-30 year old
Smoking can help
Define diarrhoea
Symptom and occurs in many conditions
Loose/watery stools
More than 3 times a day
Acute diarrhoea (less than 2 weeks)
Describe the pathophysiology of diarrhoea
Unwanted substance in gut stimulates secretion and motility to get rid of it
Primarily down to epithelial function (secretion) rather than increased gut motility
Colon is overwhelmed and cannot absorb the quantity of water is receives in the ileum
Describe diarrhoea due to osmotic causes
Gut lumen contains too much osmotic material (malabsorption)
Ingested material that is poorly absorbed
Inability to absorb nutrients
Will settle if you stop consuming offending substance
Other: too little absorption of sodium
Describe diarrhoea due to secretory causes
Electrolyte transport is messed up
Too much secretion of ions
Cause of diarrhoea will affect the messenger systems that control ion transport -> infectious toxins
Diarrhoea continues in response to fasting
Describe constipation
Suggestive if hard stools, difficulty passing stools or inability to pass stools
Straining, lumpy/hard stools, feeling of incomplete evacuation, feeling of obstruction or blockage & having fewer than three unassisted bowel movements a week
Risk factors: female, certain medications, low level of physical activity & increasing age
Describe the pathophysiology of constipation
Normal transit constipation (often related to other psychological stressors)
Slow colonic transport
Defaecation – cannot coordinate the muscles of defaecation/disorders of the pelvic floor or anorectum
Describe treatments for constipation
Psychological support Increased fluid intake Increased activity Increased dietary fibre Fibre medication Laxatives
Describe the anatomy of the appendix
Diverticulum off the caecum
Separate blood supply to caecum - ileocolic branch of SMA
Can be different locations of the appendix – retro-caecal, pelvic, sub-caecal & para-ileal
Describe the pathophysiology of appendicitis
Blockage of appendiceal lumen creates a higher pressure in the appendix
Causes venous pressure to rise (causing oedema in walls of appendix) – makes it harder for arterial blood to supply appendix -> ischemia in walls of appendix & bacterial invasion follows
Alternative explanation: viral/bacterial infection causes mucosal changes that allow bacterial invasion of appendiceal walls
Describe the symptoms of appendicitis
Poorly localised peri-umbilical pain Anorexia Nausea/vomiting Low grade fever After 12-24 hours, pain is felt more intensely in right iliac fossa (if appendix is retro-caecal or pelvic may not get this pain – might get supra-pubic pain, right sided rectal/vaginal pain instead)
Describe the signs of appendicitis
Appear slightly ill
Slight fever/tachycardia
Generally lie quite still as peritoneum is inflamed
Localised right quadrant tenderness
Rebound tenderness in right iliac fossa (relatively specific)
Describe diagnosis and treatment of appendicitis
Blood tests
History/physical examination – if classic, this may be enough
In non-classical presentations – CT scan will show distended appendix that doesn’t fill with contrast
Treatment – open appendicectomy or laparoscopic appendicectomy
Describe diverticulosis
Asymptomatic
Occurs in colon
Outpouchings of mucosa and submucosa herniate through the muscularis layers
Occurs along where nutrient vessels penetrate the bowel wall
Thought to be caused by increased intra-luminal pressure
Describe acute diverticulitis
Diverticula become inflamed or perforate +/- bleeding and abscess formation
Pathophysiology is similar to that involved in appendicitis
Uncomplicated – inflammation and small abscesses confined to colonic wall
Complicated – larger abscesses, fistula & perforation
What is diverticular disease?
The patient experiences pain but there is not inflammation or infection
Describe the symptoms and signs of acute diverticulitis
Symptoms: abdominal pain at the site of inflammation, fever, bloating, constipation & haematochezia
Signs: localised abdominal tenderness, distension, reduced bowel sounds & signs of peritonitis
Describe the diagnosis and treatment for acute diverticulitis
Diagnosis – blood tests, USS, CT scan
Treatment – antibiotics, fluid resus, analgesia & surgery if perforation or large abscesses need to be drained
Describe the anatomy of the rectum
Continuous band of outer longitudinal muscles
Curved shape anterior to sacrum
Parts of it are covered in peritoneum
Temporary storage of faeces prior to defaecation
Describe the blood supply to the rectum
Arterial supply – several arteries that form a plexus -> superior, middle & inferior rectal arteries
Venous drainage – portal drainage through superior rectal vein & systemic drainage through internal iliac vein
Describe the anatomy of the anal canal
Narrowed portion of the GI tract that continues from the rectum
Starts at the proximal border of the anal sphincter complex
Puborectalis sling changes the direction of anatomy -> anal canal points posteriorly
Contains the dentate line
-above: visceral pain receptors, columnar epithelium
-below: somatic pain receptors, stratified squamous epithelium
Describe the anal sphincter complex
Internal involuntary sphincter – thick circular smooth muscle, under autonomic control
External anal sphincter – striated muscle
-nerve supply from pudendal nerve
What are the anal cushions?
Anus contains a complex venous plexus, which is divided into 3+ areas of tissues = anal cushions
Play a role in anal continence
What are haemorrhoids?
Symptomatic anal cushions
Internal haemorrhoids – caused by loss of connective tissue support, above dentate line (relatively painless, bleed bright red/pruritis)
External haemorrhoids – swelling of the anal cushions which may then thrombose, below dentate line (very painful)
Describe the treatment for haemorrhoids
Increased hydration/high fibre diet
Avoid straining
Rubber band ligation
Surgery
Describe anal fissures
Linear tear in the anoderm – passing of hard stool, pain on defecation & haematochezia (blood in stool)
Underlying causation – high internal anal sphincter tone & reduced blood flow to anal mucosa
Treatment – hydration, dietary fibre, analgesia, warm baths & medication trying to relax the internal anal sphincter
List common causes of haematochezia
Diverticulitis Angiodysplasia Colitis Colorectal cancer Anorectal disease Upper GI bleeding
Describe melaena
Black tarry stools – offensive smelling
Due to haemoglobin being altered by digestive enzymes and gut bacteria
Common causes – upper GI bleeding -> peptic ulcer disease, variceal bleeds, upper GI malignancy
Uncommon causes – gastritis & Meckel’s diverticulum
