C16 Gastrointestinal Pathology III

Question 1

Congenital anomalies;
* Segmental anomalies of the intestine - how common, how severe, how they arise, characteristics, most common

Answer 1

• Segmental anomalies
  o Common and varying severity (stenosis to complete atresia)
  o Usually due to segmental ischemia in utero causing necrosis
  o Distention oral to the atresia, aboral segment will be small and empty

Question 2

most common segmental anomaly in horse and cow

Answer 2

• Most commonly atresia coli – spiral colon in Holstein calves, anywhere in foals
  o Genetic, possible association with rectal palpation of cows <42 days gestation?
  o Fail to pass meconium, +/- abdominal distention

Question 3

atresia ani; how it occurs, what species, associations

Answer 3

• Atresia ani
  o Hereditary in calves and pigs, possible in any species
  o Associated with vitamin A deficiency
  o Failure of perforation of the membrane separating the anus
  ectoderm from hindgut, or rectal atresia
  o Can occur alone or with other malformations (not just GI)

Question 4

• Congenital colonic aganglionosis; other name, how it arises, what is it, progression

Answer 4

• Congenital colonic aganglionosis
  o AKA lethal white foal syndrome (overo X overo breeding)
  o Defective neural crest migration means no myenteric plexus
  o No GI motility = stenosis of small colon
  o Distention of oral segments, colic and death within 48 hours

Question 5

acute GI obstructions usually occur where?chronic?

Answer 5

• Acute usually involve the upper SI, chronic involve the ileum and colon

Question 6

possible causes of GI obstructions

Answer 6

o Blockage by a luminal mass
o Stenosis due to a lesion in the wall (intrinsic)
o Extrinsic compression
o Functional (failure of muscle to contract normally), ex
adynamic ileus due to peritonitis or pain, ischemia

Question 7

what is a strangulation obstruction? common example? often accompanied by what other issue?

Answer 7

o Simultaneous obstruction and ischemia
o Ex. pedunculated lipomas in horses

Question 8

consequences of GI obstruction, despite cause

Answer 8

Regardless of cause, consequences are similar
o Fluid and gas distention and ileus oral to obstruction: may cause pressure ischemia
and eventual perforation, severe distention impairs venous outflow (congestion)
o Aboral gut is collapsed and empty

Question 9

consequences of upper GI obstructions

Answer 9

Upper GI obstructions: vomiting, dehydration
o Metabolic alkalosis (lethal if rupture does not happen first)

Question 10

consequences of lower GI obstructions

Answer 10

Lower GI obstructions: less vomiting, milder metabolic disruptions
o Allow more absorption of fluid proximal to obstruction so distention is slower
o Eventually lead to acidosis, dehydration, catabolism (once animal stops eating)
o Cecum/colon impaction in horses often cause ischemia and rupture
o Pigs with rectal stricture can have marked distention of the entire gut and abdomen

Question 11

reasons for aquired stenosis

Answer 11

o Mural abscess/hematoma, neoplasia, post-ulcerative fibrosis

Question 12

common foreign bodies, esp in cats

Answer 12

Foreign bodies
o Literally anything, obstructive by themselves or nidus for enteroliths
o Linear foreign bodies common in cats

Question 13

typical presentation of linear foreign body

Answer 13

-One end becomes fixed (base of tongue, pylorus)
-The free end stretches out and the gut pleats along it due to peristalsis
-This can ‘saw’ through the mucosa

Question 14

colon impaction - is it common? features? consequences?

Answer 14

o Common, features depend on species (but can be fecal impaction in any species)

Question 15

colon impaction in dogs - common signs and cause

Answer 15

o Voluntary suppression of defecation due to pain (inflammation, neoplasia) o Especially common with prostatic neoplasia

Question 16

colon impaction in cats - common signs and cause

Answer 16

o Megacolon in persistent obstipation (but megacolon often idiopathic)
o Manx: spinal cord problems (‘rumpies’ > ‘stumpies’)

Question 17

colon impaction in horses - common characterstics, causes, consequences

Answer 17

o Cecum/colon, mostly at sites of narrowing (pelvic flexure, transverse, small colon)
o Dehydration, coarse hay, dental disease, and sandy soil predisposes
o Can impact with feed, feces, or sand, all predispose to torsion and displacement
o Sand ingestion can cause impaction or chronic colitis

Question 18

how can extrinsic compression obstruction arise

Answer 18

o Neoplasia, abscesses, peritonitis, adipose necrosis (cows)
o Adhesions (develops gradually as the adhesion forms)
o Pedunculated lipomas (horses), incarceration in hernias

Question 19

how can a functional obstruction arise? characteristics?

Answer 19

o Adynamic (paralytic) ileus common: surgery, peritonitis, postpartum (horses)
o Segmental to diffuse, flaccid and distended intestines

Question 20

Torsion vs volvulus?
- what is each
- which is more common?

Answer 20

Torsion:
* Around long axis of organ
* Less common

Volvulus:
* Around mesenteric axis of organ
* More common

Question 21

Mesenteric volvulus
- common cause of sporadic death in what animal?
- which direction
- risk factors?
- what other species / age group, and cause?

Answer 21

o Common cause of sporadic deaths in pigs
o Usually counterclockwise, highly fermentable diet
and rock ingestion predisposes
o Also common in suckling ruminants – rapid eating leads to gas production or hypermotility

Question 22

Intussusception
- what is it?
- what orientation, usually?
- naming convention?

Answer 22

o Telescoping of one segment (intussusceptum) into another (intussuscipiens)
o Usually an oral segment into an aboral one
o Conventionally the intussusceptum is named before the intussuscipiens

Question 23

Intussusception
- age group, cause?
- associated with what?
- causes what? signs?
- limited by what?
- sequelae?
- problems that affect surgical correction?

Answer 23

o Often young animals and idiopathic, can be associated with linear foreign body, parasites, enteritis, previous surgery, mural lesions, or agonal
o Usually cause partial to complete obstruction +/- blood in feces
o 3 layers, length limited by degree of tension on the mesentery
o Tension and compression of mesenteric veins cause infarction of intussusceptum
o Adhesions form and prevent reduction, usually leading to necrosis and gangrene

Question 24

Intussusception
- which part is dilated, vs empty and contracted?
- most common spot in dogs?
- ever in lambs, calves?
- associated with what in horses, and location?

Answer 24

• side of ‘inner’ part may be dilated
• side of ‘outer’ part may be empty and contracted
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  dogs
• Most common
• Usually ileocolic
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  occasional in labs, calves
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  in horses:
• Cecocolic associated with tapeworms, Salmonella, cyathostomes

Question 25

Eventration
- what is it?
- cause?

Answer 25

• Eventration: displacement outside the abdominal cavity
  o Often congenital, ex. schistosomus reflexus, patent umbilicus, diaphragmatic hernia
  o Acquired often related to trauma, can be external, subcutaneous, intramuscular

Question 26

Cecal and colonic dilation, tympany, and torsion
- common in cows? when?
- cattle risk factors? pathogenesis?
- pathogenesis in horse?
- causes what problems?
- sequelae? survivors may get what?

Answer 26

o Uncommon in cows, usually within 2 months postpartum
o High concentrate rations predispose (increased VFAs -> atony -> distention -> rotation)
o Similar pathogenesis in horses
o Compresses abdominal organs, venous return, and diaphragm (dyspnea)
o Painful, may die of hypovolemia or acidosis before rupture occurs
o Acidosis causes mucosal ulceration -> endotoxin absorption -> laminitis in survivors

Question 27

why is the horse colon prone to displacements

Answer 27

• The horse colon is only attached near the cecum (prone to displacements)

Question 28

Right dorsal displacement of the horse colon
- what is this? orientation?
- visible on PM when opened in what position
- how does this progress?
- Tx?

Answer 28

o Pelvis flexure ends up pointing cranially, leading to obstruction and colic
o Visible when carcass is opened in left lateral
o Often starts with pelvic flexure impaction and often some degree of torsion is present
o Surgical correction required
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- Heavy impacted pelvic flexure moves cranioventrally
- This pulls the right colons ventral to the cecum
- Right colons distend with gas, float up and twist

Question 29

Left dorsal displacement (AKA nephrosplenic entrapment) in the horse?
- how does this occur?
- may cause what?

Answer 29

o Left colons move dorsally between the spleen and body wall
o They get stuck between the spleen and kidney, and rotate so the ventral colon is dorsal
o Nephrosplenic ligament laxity predisposes but the cause is usually unknown
o May cause impaction, colonic ischemia, or compress splenic vein (congestion)
o Colic signs are intermittent if not impacted

Question 30

Colonic volvulus in the horse
- common cause of what?
- leads to?
- what happens?
- possible consequences?

Answer 30

o Common cause of colic, leads to venous infarction
o Right ventral colon rotates 270-720°
o If >360°, causes obstruction, ischemia, enterotoxemia
o May involve part of the cecum
o Can lead to postmortem diaphragmatic rupture due to pressure from trapped gas
and/or ingesta

Question 31

Internal hernia
- common?
- anatomy?

Answer 31

o Uncommon, can be through normal or pathological foramina, no hernial sac
o Natural foramen: mostly epiploic foramen SI entrapment in horses
o Omental/mesenteric hernia: entrapment in a tear, usually traumatic and involve SI

Question 32

External hernia
- what is it? anatomy?
- contents?
- sequelae?
- what is incarceration and what may it lead to?

Answer 32

o Natural or acquired hernial sac of peritoneum covered by skin and soft tissue
o Hernial ring at the base connects to the abdomen
o Usually contain omentum, intestine, +/- other organs
o Sequelae depend on location and contents, if freely mobile usually no sequelae
o Fixation (incarceration) due to stenosis, adhesions, or distention is serious, may lead
to necrosis, obstruction, perforation, and peritonitis

Question 33

Ventral abdominal wall hernia
- uncommon in what species?
- anatomy?
- spontaeous when?

Answer 33

o Uncommon in horses and cattle
o Herniation into subcutis
o Spontaneous in late pregnancy (rule out ruptured prepubic tendon) or traumatic

Question 34

Umbilical hernia
- common?
- cause?
- risk factors?
- species?

Answer 34

o Common, congenital, sometimes heritable (Holsteins)
o Patency of the umbilical ring, omphalitis predisposes
o The most common congenital defect in calves but occurs in all species

Question 35

Perineal hernia
- moslty what species, signalment? concurrent dz?
- cause?
- anatomy? possible issue?

Answer 35

o Mostly old male dogs with prostatic enlargement and obstipation
o Weakening of perineal muscles combined with pressure from straining
o Mostly unilateral but can be bilateral
o Usually only contain fat but sometimes bladder is involved and may obstruct

Question 36

Diaphragmatic hernia
- common? cause?
- anatomy? rare issue?

Answer 36

o Common, usually acquired but sometimes congenital
o Liver and SI most likely to herniate, strangulation is rare

Question 37

Inguinal hernia
- inguinal ring anatomy?
- can progress to what in males?
- possibility in bitches?
- 2 main types?
> how they arise
> how common
> how serious, sequelae
> signalment

Answer 37

o Inguinal ring is patent in intact males of all species and in the bitch
o In males, herniation can progress to scrotal hernia (leading to testicular degeneration,
castration complications…)
o In bitches, uterine herniation and strangulation is possible
o Two main types…
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* Direct inguinal hernia
o Herniation through a tear in the peritoneum
o Less common and life-threatening (often cause skin necrosis, become fixed by adhesions and strangulate)
o Most frequent in foals (due to pressure of parturition)
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* Indirect inguinal hernia
o More common, contents are contained in the tunica vaginalis
o Congenital in young animals (more common in male dogs)
o Acquired in adults but often idiopathic (more common in bitches)

Question 38

inchemia and infarction of the GI tract are especially common in what species?

Answer 38

horses

Question 39

if we have intestinal ischemia and infarction, what is the progression of damage?

Answer 39

tips of villi:
- ischemic lesions in 5-10 minutes
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villi:
- Complete epithelial loss and hemorrhage in 1-3 hours
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- Colon less sensitive
> Mild damage 1 hour
> Necrosis 3-4 hours
> Can cause chronic diarrhea and cachexia
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crypts:
- Begin disintegrating in 2-4 hours
- Completely gone in 4-5 hours
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- Tunica muscularis survives for 6-7 hours, contractility permanently lost if ischemic >4-6 hours

Question 40

Ischemia and infarction
- intestinal sample consideration for diagnostics
> timing

Answer 40

MUST FIX QUICKLY FOR DIAGNOSTICS!

Question 41

Ischemia and infarction
- when is reperfusion injury possible?
> resembles what?
> less likely in what species?

Answer 41

• Reperfusion injury is possible if necrosis is not complete and ischemia is transient
  o Resembles hypoxic injury, less likely in pigs and horses

Question 42

Ischemia and infarction
* Sequelae depend on?
- preservation vs loss of crypts?
- complete ischemia?

Answer 42

• Sequelae depend on duration and severity of ischemia
  o Preservation of crypts: regenerates in 1-2 weeks (except necrotic muscularis mucosa),
  inflammation persists until the epithelium is restored
  o Loss of crypts: ulceration and surrounding inflammation, healing by granulation followed by re-epithelialization from adjacent surviving mucosa
  > Extensive ischemic ulcers covering large areas don’t heal (often have a fibrinonecrotic
  covering, act as portals for bacteria)
  > In survivors, chronic ulcers may lead to stricture
  o Complete ischemia: full-thickness necrosis (green-black and friable), proliferation of
  anaerobes (produce toxins and gas), gangrene, endotoxemia

Question 43

The most common cause of GI ischemia?
- why?
- causes?
- appearance?
- sequelae?

Answer 43

• Venous infarction
  o The most common cause of GI ischemia (thin-walled veins compress more easily)
  o Incarcerated hernias, pedunculated masses, torsion, volvulus, intussusception
  o Displacements can progress to infarction (common cause of colic in horses)
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• Edema, congestion, hemorrhage (red-black)
• Sharp demarcation
• Bloody, gaseous contents
• Progressive gangrene turns green-black
• Leads to septic peritonitis regardless of whether it ruptures

Question 44

Arterial thromboembolism in hose
- any other species?
- associated with?
- anatomical location
- appearance?

Answer 44

o Rare other than horses, mostly associated with emboli from secondarily infected thrombi (ex. S. vulgaris)
o Most common at watershed regions with limited collateral circulation
> rectum, pelvic flexure, tip of cecum
o Necrotic areas are grey-brown if there is no reperfusion but resemble venous infarction if reperfused (distribution will be different)

Question 45

Shock gut
- mostly what species?
- pathogenesis?
- leads to?
- appearance?

Answer 45

o Mostly in dogs, hypoxia due to reflex vasoconstriction and capillary dilation
o Leads to pooling of blood, hypotension, and microthrombi
o Congested SI mucosa and hemorrhagic contents

Question 46

Reduced perfusion – NSAIDs
- species?
- how do we get mucosal ischemia?
- range of possible problems?
- in horses, anatomic location
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- what if dehydrated?

Answer 46

o Causes GI ulceration in horses (even at therapeutic levels) and dogs
o Microvascular damage and/or vasoconstriction -> mucosal ischemia
o Ranges from congestion and edema to erosion and ulceration
o In horses, mostly right dorsal colon
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Renal papillary necrosis – common if dehydrated

Question 47

Malassimilation and protein loss
- species?
- causes?
- lead to?
- requirement for diagnosis and prognosis?

Answer 47

• Mostly seen in dogs but also diagnosed in horses and cats
  o Usually idiopathic but many possible causes (neoplasia, amyloid, lymphangiectasia,
  some infectious agents)
  o All lead to chronic diarrhea, weight loss, and hypoproteinemia
  o Biopsy required to diagnose and give a prognosis

Question 48

Amyloidosis
- where is it deposited? visible grossly?
- problems caused?

Answer 48

o Deposited in GI tract in systemic amyloidosis, usually not visible grossly
o Impairs fluid uptake and/or increases
capillary permeability, leading to protein loss

Question 49

Lymphangiectasia in dogs
- usual cause?
- clinical signs due to?
- appearance?
- sequelae?
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- appearance, gross and histo

Answer 49

o Usually due to acquired lymphatic obstruction (inflammation, neoplasia)
o Often no cause can be identified, clinical signs due to malabsorption
o Transmural lymphatic and lacteal dilation +/- lipid laden macrophages
o Hypoalbuminemia leads to ascites and peripheral edema
<><><><>
- Thickened, edematous mucosa with white spots
- Prominent serosal lymphatics
- Dilated crypts with inflammatory cells (‘crypt abscess’)

Question 50

Idiopathic inflammatory bowel disease (IBD)
- species?
- is it a specific disease?
- why can it be hard to confirm?
- hard to differentiate from what other dz?

Answer 50

o Mostly dogs and cats, sometimes horses and cows
o Clinical syndrome rather than a specific disease, likely multifactorial
o Diagnosis of exclusion but hard to confirm due to overlap between pathology and
normal variation, lesions often mild compared to clinical signs
o Inflammation can be hard to differentiate from early lymphoma

Question 51

Eosinophilic enteritis in cats
- common? may be part of what syndrome? age?
- what happens?
- signs?

Answer 51

o Rare, may be part of systemic hypereosinophilic syndrome (middle aged-old)
o Differentiated eosinophils infiltrate many tissues (SI, liver, spleen, LNs - enlarge)
o Severe diarrhea +/- blood, vomiting, weight loss, peripheral eosinophilia

Question 52

Eosinophilic enteritis in horses
- may be part of what disease?
- signs?
- lesions
- cause?

Answer 52

o May be part of multisystemic epitheliotropic syndrome, chronic disease
o Weight loss and diarrhea +/- pancreatitis, dermatitis, no peripheral eosinophilia
o Thickening of GI mucosa anywhere in the tract
o Cause unknown, sometimes GI lesions occur alone