Pathology of the peritoneal cavity Flashcards
Developmental and acquired abnormalities of the peritoneal cavity
Atresia
- ani
- coli
Megacolon
Atresia
Anomalous development of the intestinal wall with occlusion of the lumen.
E.g. atresia ani (imperforate annus – most common congenital defect of the lower GIT) and atresia coli (most common segmental anomaly of the intestine in domestic animals).
Animals are unable to defecate, develop peritonitis.
Megacolon
Diffuse dilation of the colon, usually faecal-filled colon.
It can be congenital or acquired in dogs and cats.
If congenital – lack of myenteric plexuses (Hirschsprung’s disease), due to absence of neuroblast migration to colorectal myenteric plexuses.
If acquired – secondary to damage to the colonic innervation (traumatic – struck by automobiles).
Hernia
a loop of intestine protruding through a normal hole e.g. umbilical or scrotal.
Rupture
protrusion through an abnormal hole, usually traumatic.
Pathogenesis of a strangulated hernia/rupture
Usually umbilical / inguinal. Peritoneum usually intact and thus easy to treat.
Ruptures often have damaged peritoneum and this may twist round to strangulate bowel producing same effect as volvulus.
Rupture of diaphragm in small animals with stomach and intestines passing into thorax.
Eventration
Protrusion of abdominal viscera through an open abdominal wall.
Volvulus / torsion of the intestine
These are rare in dogs.
Volvulus is twisting of the intestine on its mesenteric axis (long axis). Twist in loop of intestine, which is intensely congested, often almost black. Torsion of the intestine is a rotation along its long axis.
Mostly in young animal especially dogs.
Pathogenesis of volvulus/torsion of the intestine
Normally affects small intestine.
Loop of bowel twists through 180 degrees around mesentery to produce obstruction of lumen.
Bowel becomes rapidly distended proximal to obstruction and produces rapid death.
First venous return is shut off but arterial flow is still present and bowel becomes engorged with blood.
Bowel becomes hypoxic.
Toxic material and bacteria pass through the anoxic wall of bowel.
Intussusception
Intussusception is when one segment of intestine becomes telescoped into the immediately distal segment of intestine.
Where is the most common location of an intussusception in the dog?
Ileocolic
Clinical signs of intussusception
Less acute type of obstruction.
Produces intermittent diarrhoea and go downhill in few days.
If you palpate abdomen may feel “Cumberland sausage” effect (abdominal palpation in small animal, rectal in large).
Pathology of intussusception
When operate or at post mortem see large sausage shaped distension of length of intestine.
Pathogenesis of intussusception
Blood supply cut off producing necrosis of bowel.
There is often functional obstruction to bowel.
May be adhesions between layers of mucosa.
May slough off internal portion by digestion and heal or may rupture leading to peritonitis and death.
Associated with intestinal irritability and hypermotility e.g. change in diet, bacterial infection, parasites, foreign bodies, neoplasms, handling of the small intestine during surgery.
Adhesions (fibrinous) occur after approximately 24 hours and then cannot pull the intussusception apart.
Clinical signs of intestinal obstruction
May be acute or slowly developing.
Not many clinical signs - vomiting (in animals which can vomit).
Emergency situation as many individuals die from shock very rapidly (sometimes complicated by bowel rupture and peritonitis).
Severity of symptoms and rapidity of progression depends on level of obstruction.
○ High: Fluid accumulates proximally to obstruction. Vomiting produces loss of chloride and potassium with development of metabolic alkalosis.
○ Low: More chronic. Some resorption of fluid and electrolytes.
Metabolic acidosis eventually from starvation and muscle metabolism.
