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.
Intestinal foreign bodies - incidence
Quite common in dogs, rare in other species (as tend to lodge in oesophagus or in ruminants in one of the stomachs).
Clinical signs of intestinal foreign bodies
Obstruction at pylorus produces repeated vomiting.
Lower down less dramatic effect but still a problem if in middle of small intestines.
May be vague signs, some vomiting and off food.
Diagnosis of intestinal foreign body
for a while (up to several days) may not show up well radiographically (unless radio-opaque).
May also be objects that are semi solid or soft. E.g. string, plastic bags, stringy things like pieces of material- particularly in puppies.
Make all of intestines have knotted appearance (may appear like gastritis) - may be seen in horses with baler twine.
Pathogenesis of intestinal foreign body
In intestines smooth round objects such as golf balls lodge especially near the pylorus or lower down.
Occasionally in cattle (piece of rope or piece of tarpaulin) produces a tangled mass in rumen.
Clinical signs of an obstructing tumour in the intestines
Occasional vomiting, intermittent diarrhoea over several weeks.
Pathogenesis of an obstructing tumour in the intestines
Seen occasionally in cat (rarer in dog) usually towards end of intestines - e.g. ileocaecocolic valve.
Gut proximal to tumour becomes thickened due to hypertrophy of smooth muscle as a result of trying to force ingesta past progressively narrowing lumen.
Produces “hose pipe intestine”.
See with carcinoma, lymphoma, mast cell tumour, leiomyoma and other tumours.
Pathogenesis of infarction in the intestines
Relatively rare as good anastomosing blood supply to bowel.
Now mainly seen in small animals, especially dogs and cats, due to road traffic accidents producing infarct in gut.
Also with renal disease, particularly nephrotic syndrome where there is a prothrombotic state in the circulation generally due to loss of anticoagulant proteins in urine.
There is often a functional obstruction at point of infarction.
Pathology of an intestinal infarction
See sharply delineated dark areas in bowel that are flaccid with loss of tone.
These become necrotic followed later by peritonitis.
Rectal prolapse
Downward discplacement of the instestines through the rectum and anus
Paralytic ileus
Neurogenic obstruction
Or adynamic ileus, is a non-mechanical hypomotility resulting in functional obstruction of the bowel.
Stasis of gut flow due to failure of peristalsis.
No real obstruction - pseudo-obstruction.
Causes of paralytic ileus
Anything which stops peristalsis, e.g. damage to nerve supply to intestine (autonomic nervous system), pain, abnormal metabolism, toxaemia and electrolyte imbalance such as hypocalcaemia, hypomagnesaemia, and hypokalaemia.
Also diabetes mellitus, uraemia, tetanus and lead poisoning.
Pathology of neurogenic ileus
Bowel flaccid, loss of tone of smooth muscle, bowel distended with fluid.
Pathogenesis of neurogenic ileus
Intestine susceptible to neurogenic damage during an operation, peritonitis, shock, severe pain, abnormal stimulation of splanchinc nerves, toxaemia, uraemia, tetanus, heavy metal poisoning.
Peristalsis fades away over a few days producing paralytic (adynamic) ileus.
Particularly occurs if bowel handled roughly, or if serosa gets cold and dry at surgery.
Very difficult to start peristalsis again but will sometimes respond to pharmacological or electrical stimulation.
Peritonitis
Inflammatory exudate presents in abdominal cavity.
May contain large amounts of fluid.
With paralytic ileus, intestines fill with fluid, which contributes to hypovolaemic shock.
Bowel is flaccid with loss of tone and congestion.
Adhesions between loops of bowel may develop.
Causes of peritonitis
Several causes e.g. Feline Infectious Peritonitis (FIP), urine in abdomen, gastric rupture, perforating gastric ulcers, cholecystitis / gallbladder rupture, intussusception, volvulus, gastric or intestinal torsions.
FIP
Feline infectious peritonitis
a fatal disease of cats.
Two presentations of disease: “wet form” (fibrinous polyserositis) and “dry form” (pyogranulomas).
Affects principally young and old cats
12% of feline deaths are associated with FIP
Due to a coronavirus related to TGE of pigs
Pathogenesis of FIP
Feline coronavirus within salvia on shared bowls and utensils/faeces /mutation of endogenous coronavirus
Viral replication in epithelial cells of the intestine/lymph nodes
Infected macrophages
Viraemia
Endothelial cells are activated secondary to up-regulation of MHC
Systemic vasculitis
Peritonitis, granulomatous nephritis, pleuritis, uveitis, meningitis, etc.
Diagnosis of FIP
Clinical signs
□ Progressive weight loss
□ Abdomen distension
□ Behavioural changes
□ Etc.
Macroscopic and microscopic lesions (cytological findings)
IHC
Ascites
Hydroperitoneum
Oedema in the peritoneal cavity characterised by clear to slightly yellow (straw) fluid with a small amount of protein.
It is a transudate.
Causes could be the same as other oedemas e.g. increased intravascular hydrostatic pressure, decreased intravascular osmotic pressure, decreased lymphatic drainage, and increased microvascular permeability.
Haemoperitoneum
It refers to the presence of frank blood within the peritoneal cavity.
It can be the result of rupture of a large blood vessel in the cavity, rupture of spleen, liver or a splenic haemangiosarcoma.
Chyloperitoneum
It is the presence of chyle in the peritoneum.
This is rare, can be due to obstruction or trauma to the thoracic duct.
Pyoperitoneum
Pus in the peritoneal cavity, usually as a result of a peritonitis.
Pyopneumoperitoneum refers to the presence of pus and gas in the peritoneal cavity.
