Pathology of Intestinal Obstruction Flashcards
Where can obstructions of the GIT occur?
At any level of the GIT
Which organ of the GIT is most commonly involved with mechanical obstructions? Why?
Small intestine is most often involved because of its relatively narrow lumen
What are examples of the most common mechanical obstructions?
Hernias
Intestinal adhesions
Intussusception
Volvulus
What is a less common example of mechanical obstruction?
Luminal masses
What are the clinical manifestations of mechanical obstructions?
Abdominal pain and distention
Vomiting
Constipation
What is intussusception?
When a segment of bowl is drawn into a distal segment
What causes intussusception?
Peristalsis pushes a part of bowel distally into an adjacent segment, causing it to telescope
What is the pathogenesis behind intussusception?
- Associated with leading edge
- Telescoped segment is pulled forward by peristalsis, resulting in obstruction
- The mesentery and blood vessels accompany the bowel and can become compressed, leading to edema, ischemic damage, and entrapment
Where is intussusception most common to arise (which region?)
Ileocecal region
In adults, what serves as the leading edge for intussusception?
Tumor or polyps
In children, what is the leading edge for intussusception?
Lymphoid hyperplasia (enlargement of lymphoid tissue) due to rotavirus or adenovirus infection
What is volvulus?
Twisting of the bowel along its mesentery
What is the result of volvulus?
Results in obstruction and disruption of the blood supply with infraction
What are the most common location for volvulus to occur in elderly and young ones?
Sigmoid colon –> elderly
Cecum –> young adults
What is the etiology behind volvulus? (3)
- Pregnancy –> fetus can cause displacement and twisting of the colon
- Chronic constipation –> Hirshsprung disease
- Abdominal adhesions
What are adhesions?
Bands of fibrous tissue (from previous surgery) that can connect
What are different examples of adhesions?
- The loops of the intestines to each other
- Intestines to other abdominal organs
- Intestines to the abdominal wall
How do adhesions cause obstructions?
- Kinking or angulating the bowel
- Directly compressing the lumen
What is Hirschprung disease?
Dilation of the colon which results from the congenital absence of ganglion cells, usually in the wall of the rectum
What is is the epidemiology of Hirschprung disease?
Occurs in 1 of 5000 live births
More common in males, but tends to be more severe in females
What is the pathogenesis of Hirschprung disease?
- Mutations in the receptor tyrosine kinase RET
- Disruption in normal migration of neural crest cells from cecum to rectum
- This produces a distal intestinal segment that lacks both Meissner submucosal plexus and Auerbach plexus myenteric plexus
- This aganglionic segment is permanently contracted because of the absence of tonic relation neural stimuli
- As a result, fecal contents cannot readily enter the contracted area
What is the gross morphology of Hirschprung disease?
Progressive dilation as a result of the distal obstruction
What is the histology of Hirschprung disease like?
Absence of ganglion cells in the affected segment
What are the clinical features of HIrschprung disease?
Failure to pass meconium in the immediate postnatal period followed by obstructive constipation
What are the complications of Hurschprung disease?
- Enterocolitis
- Fluid and electrolyte disturbances
- Perforation
- Peritonitis
What causes the formation of an abdominal hernia?
Abdominal herniation may occur through any weakness or defect in the wall of the peritoneal cavity, including inguinal and femoral canals, umbilicus, and sites of surgical scarring
What is a hernia sac?
Protrusion of serosa-lined pouch of peritoneum
What is the pathology of abdominal hernias?
- Pressure at the neck of the pouch may impair venous drainage, leading to stasis and edema
- These changes increase the bulk of the herniated loop, leading to permanent entrapment
- Over time, there is a compromise of arterial supply and venous drainage (strangulation), leading to ischemic necrosis (infection) and gangrene
What is diverticulosis?
Refers to acquired pseudodiverticular outpouchings of the colonic mucosa and submucosa through the muscularis propria
What are the predisposing factors of divertciculosis?
Age (rare in people < 30)
Low fibre diet
Use of corticosteroids
Use of NSAIDs
What is the pathogenesis of divericulosis?
- Diet low in fiber, reduces the stool bulk
- Elevation in intramural pressure in the sigmoid colon
- Unique structure of colonic muscularis propria (where nerves, arterial vasa recta, and their CT) sheaths penetrate the inner circular muscle coat to create discontinuities in the muscle wall
What is the gross morphology of diverticulosis?
- Small
- Flask-like outpouching (0.5 to 1 cm)
- Regular distribution between Taeniae coli
What is the histopathology of diverticulosis?
Diverticula have a thin wall composed of:
1. Flattened and atrophic mucosa
2. Compressed submucosa
3. Attenuated muscularis propria (often absent even)
What is pseudo-obstruction?
In pseudo-obstruction, symptoms and signs of obstruction occur but without any of the mechanical lesions
What are the two types of pseudo-obstruction?
- Primary pseudo-obstruction
- Secondary pseudo-obstruction
What is primary pseudo-obstruction?
Smooth muscle may become replaced by fibrous tissue leading to profoundly altered motility
It may occur as a familial condition
What is secondary pseudo-obstruction?
- May arise as a complication of well0-defined systemic disease
- Scleroderma, which interferes with normal smooth muscle function
- Amyloisosis and endometriosis may similarly affect the muscularis and cause secondary pseudo-obstruction
WHat is the end result of pseudo-obstruction?
Impair gut motility by affecting smooth muscle cells and/or their neural inputs
