Meckel's diverticulum & intestinal obstruction

Question 1

What is the cause of Meckel’s diverticulum?

What is Meckel’s diverticulum - where?

Answer 1

• Caused by a remnant of the embryological vitelloinstestinal duct (2% of population have it)
• Only 2% of people with Meckel’s develop symptoms
• The diverticulum is 2cm long, on the antimesenteric border of the bowel, 20 inches from the ileocecal valve
• It may be lined by gastric acid secreting epithelium, or heterotropic pancreatic tissue

Question 3

What are the possible patholigical effects of Meckel’s diverticulum?

Answer 3

• Caecal volvulus​
  
  • part of the colon twists on its mesentery, resulting in acute, subacute, or chronic colonic obstruction
  • ​If tethered to the umbilicus, the diverticulum may act as the apex of a volvulus to present like a volvulus with obstruction
• Intussusception
  
  • Part of the intestine folds into the section next to it​
  • ​Often gangrenous by the point of operation
• Appendicitis
  
  • ​Diverticulum becomes inflamed, presenting identical to appendicitis (sometimes also with umbilical cellulitis)
• Peptic ulceration
  
  • ​Pain around umbilicus that is related to mealtimes, due to ulceration of the gastric acid secreting epithelium
• A sinus tract may also exist between the diverticulum and the umbilicus (patent viteloointestinal duct)

Question 4

Describe the signs and symptoms in a patient with intestinal obstruction

Answer 4

Symptoms:

• Vomiting
  
  • Undigested food suggests gastric outlet obstruction
  • Bilous vomiting suggests upper small bowel obstruction
  • Faeculent vomiting (thicker/foul-smelling) suggests more distal small bowel obstruction
• Pain
  
  • Colicky abdominal pain in early obstruction
  • Pain may be absent in long-standing obstruction
• Constipation
  
  • May not be absolute (no passage of wind) in proximal obstruction

Signs:

• Distention
• Tinkling bowel sounds
• Dehydration
• Central resonance to percussion, dull flanks
• Scars: previous surgery causing adhesions
• Palpable mass (causing obstruction)
• NO abdominal tenderness (unless strangulation)

Question 5

List the common causes of small bowel obstruction

Answer 5

• Adhesions (80%) - extramural
• Hernias - extramural
• Crohn’s disease - intramural
• Intussusception (part of the intestine folds into the section next to) - intramural

Question 6

List the common causes of large bowel obstruction

Answer 6

• Carcinoma of the colon - intramural
• Diverticular disease - intramural
• Sigmoid volvulus - extramural
• Constipation (forgein body or faecal impaction ect) - intraluminal

Question 7

What are the complications of bowel obstruction?

Answer 7

• The bowel wall becomes oedematous (tissue with excess interstitial fluid) and distends
• Bacteria proliferate in the obstructed bowel
• As the bowel distends, vessels become stretched and the blood supply is compromised, leading to strangulation (→ ischaemia & necrosis)
• Eventually the bowel will perforate
• Symptoms develop more gradually in large bowel obstruction due to the capacity (even greater if the ileo-caecal valve is incompetent)

Question 8

Interpret these AXRs

Answer 8

Bowel obstruction on AXR; (1) Small bowel obstruction, showing valvulae conniventes crossing a dilated, centrally-located bowel; (2) Large bowel obstruction, with peripherally located dilated bowel segments

Small bowel - >3cm = dilated. The valvulae conniventes run the whole way across the small bowel

Large bowel - >5cm = dilated. The haustra do not run the whole way across the large bowel.

Question 9

What investigations should be done for a patient with suspected small intestinal obstruction?

Answer 9

• Bloods: FBC, U&Es, Amylase, LFTs
• ABG
• Urinalysis
• Supine AXR: distened proximal bowel, absent gas distally
• Erect CXR: fluid levels in small bowel obstruction, air under diaphragm if perforation
• Contrast enema: differentitates obstruction and pseudo-obstruction, can identify the level of obstruction and ileo-caecal competency (gastrograffin may also have therapeutic effect)
• CT scan: can indicate level of obstruction, but cannot always give the diagnosis

Question 11

Compare and contrast small to large bowel obstruction

Answer 11

Vomiting:

• Absent/faeculant in LBO
• Bilous in SBO

Constipation:

• Absolute in LBO
• May not be absolute in SBO

Progression:

• More rapid in SBO

The best differentitator is plain film radiograph of the abdomen