Pathology of Alimentary Tract 2 (Ruminant Forestomachs/ Glandular stomach)

Ruminant Forestomachs
1. Forestomachs: Rumen, Reticulum, Omasum
2. Note: Postmortem putrfactive changes occur rapidly (Gas distension, Sloughing of mucosa)
3. Functional Disorders
  1. Bloat (Ruminal Tympany)
    1. Failure to expel fermentation gases
    2. Pathogenesis:
      1. Primary:
        "Frothy bloat"
        Due to formation of stable foam in Rumen (follows ingestion of excess high protein lucerne/clover or high concentrate, low roughage diet
      2. Secondary:
        Mechanical/functional obstruction of oesophagus (oesophageal stricture) -> accumulation of gas
        Vagus indigestion (Traumatic reticuloperitonitis, liver abscess, chronic suppurative bronchopneumonia)
        Recurrent laryngeal nerve & Vagus nerve => Vagal function => Reduced Rumen Motility
        Neoplasia (Lymphoarcoma, Papillomas)
    3. Overdistension of Rumen & Reticulum with fermentative gases
      1. Increased intra-abdominal pressure
        Congestive heart failure
        Compression of diaphragm
        Resp. failure
        "Bloat line" cranial to thoracic inlet
        Reduced return of blood flow to heart
        Blood is dark (Hypoxic) & clots poorly
        Congestion, Oedema & subcutaneous haemorrhage of head & neck tissues
  2. Runminal Acidosis (Grain overload)
    1. Ruminitis may develop => allow thromboemboli to travel to the Liver => Hepatic abcessation
      1. Histologically: Microvesicles containing mainly neutrophils occur in the epithelium of the rumen papillae
        May be focal erosions/ulcerations
        Damaged mucosa may be colonized by fungi (e.g. Mucor/Rhizopus/Absidia app.) or bacteria (e.g. Fusobacterium necrophorum)
4. Inflammation
  1. Traumatic Reticulitis "Hardware disease"
    1. Ingestion of sharp objects (e.g. wire, nails)
    2. 1) Fall to floor or reticulum => Insignificant
    3. 2) Contractions force foreign body into wall of reticulum:
      1. => Mild suppurative or Granulomatous reticulitis +/- Peritonitis
        Localized => Adhesions
    4. 3) Foreign body penetrates Cranial wall (rumen contractions) :
      1. => Acute Peritonitis, Local Fibrous adhesions
        => Penetrates Diaphragm (Fibrinopurelent pleurisy, pneumonia, pericarditis)
        Fusobacterium, Actinomyces spp.
    5. Inflammatory process around Reticulum (may) => vagus indeigestion & ruminal stasis
    6. => Purulent fluid build up => Cardiac Failure
  2. Ruminitis (Bacterial or Mycotic)
    1. Bacterial
      1. Lactic Acidosis
        Opportunistic pathogens (Take advantage of acidotic lesions & other disturbances of rumen flora)
      2. Mechanical Injury to Rumen
        Ex. Traumatic Reticuloperitinitis
        Damage to Rumen wall => Infiltration of bacteria (GI colonizers)
      3. Fusobacterium necrophorum, Trueperella pyogenes, Actinobacillus lignieresii
    2. Mycotic
      1. Abx, Lactic Acidosis
      2. Vascular invasion -> Thrombosis -> Infarction
      3. Haematogenous -> Placentitis -> Abortion
      4. Mucor/Rhizopus/Absidia
    3. Gross: Multiple, dark red areas of swollen paillae, Coagulative necrosis of papillae, Serofibrinous exudate
    4. Histologically: Coagulative necrosis of papillae, marked neutrophil infiltrate
    5. Thromboembolic spread => Form areas of coagulative necrosis & abscesses in Liver
5. Neoplasia
  1. Papillomatosis
    1. Bovine papillomavirus type 4
    2. Usually pedunculated structures in Reticulum/Rumen of Cattle
  2. Squamous cell carcinoma
    1. Thought to develop from papillomas in Cattle in association with ingested carcinogens in Bracken Fern
Pathology of the Glandular Stomach & Abomasum
1. Physical Disturbances
  1. Obstruction
    1. Foreign body
      1. Bones, stones, hair/wool balls (trichobezoars), plant material (phytobezoars)
    2. Pyloric Stenosis
      1. Dogs, Foals, Cats
      2. Congenital Hypertrophy of Pyloric muscle
        => Delayed Gastric emptying & persistent vomiting/regurgitation
      3. Acquired
        Following healed ulcers (foals)
    3. Functional Obstruction
      1. Dysautonomia
        Feline dysautonomia
        Equine Grass sickness
      2. Vagal indigestion (Cattle)
      3. End-stage liver disease (Equine)
    4. Horses DON'T vomit! Stomach will rupture before they vomit
  2. Displacements of the stomach/abomasum
    1. Herniation of Stomach (through diaphragm)
      1. Congenital (Cats)
        Often associated w/ herniation of Liver
        Peritoneo-pericardial diaphragmatic hernia
      2. Acquired (Dogs, Cats)
        RTAs
        Displacement of GI tract into peritoneal cavity
    2. Abomasal Displacement (Cattle)
      1. Ventral & to left of Rumen (LDA)
        85% of Displacements
        Partial obstruction of outflow
        Mild consequences: May not require surgery
      2. To right of Rumen (RDA)
        15% of Displacements
        Acute dilation & volvulus
        Severe consequences: Usually require surgery
        Obstructs outflow from abomasum
      3. Normal location: Close to or just right of the ventral midline
      4. Constriction of blood vessels & trauma to vagus nerve resulting in abomasal distension w/ blood-stained fluid & gas, congested mucosa, infarction
        May rupture => Peritonitis, shock, death
        NOTE: Gastric rupture may be a PM event due to putrefactive gases (Look for evidence of haemorrhage & Peritonitis suggesting antemortem rupture
      5. Predisposing factors:
        Post-parturient Dairy Cows
        Change to grain concentrates in diet (Increased VFAs -> Affect motility)
        Hypocalcaemia (Abomasal atony)
2. Inflammation
  1. Haemorrhagic/necrotizing Abomasitis
    1. Braxy
      1. Sheep/Cattle
      2. Acute abomastitis (Red, thickend, necrotic haemorrhagic mucosa
        Ingestion of frozen food in winter
        Devitalizes gastric mucosa
        Coagulative necrosis of mucosa & deeper structures w/ fibrin, oedema, haemorrhage & sometimes submucosal emphysema
      3. Clostridium septicum (Exotoxin)
  2. Bacterial Gastritis & Gastric Ulceration
    1. Heliobacteriosis
      1. Dogs, Cats
      2. Helicobacter heilmannii, Helicobacter felis
      3. Chronic mucoid gastritis
  3. Hypertrophic Gastritis/ Abomastitis
    1. Chronic hypertrophic gastritis (Dogs)
      1. Chronic retention of gastric fluid & bile reflux
      2. Marked mucosal thickening & convolution of rugae
        Histologically: Marked epithelial hyperplasia, loss of parietal/chief cells, dilation of mucous glands & mixed inflammatory cell infiltrates in lamina propria
    2. Parasitic Gastritis (Osteragiosis)
      1. Cattle: Ostertagia ostertagi
        Sheep: Teladorsagia circumcincta
      2. Acute Gastritis
        Hyperaemia & oedema
      3. Chronic Gastritis
        Nodules (encysted larvae) in abomasal mucosa, "Morocco leather" appearence
      4. Glandular hyperplasia, loss of parietal/chief cells, chronic inflammation associated w/ lymphocytes, plasma cells & eosinophils & larvae
  4. Chronic Atrophic Gastritis (Dogs)
    1. Aetiology uncertain
      1. Mucosal thinning & loss of gastric glands, diffuse mixed inflammtory infiltrate in the lamina propria
3. Ulceration
  1. Pathogenesis
    1. Hypersecretion of acid &/or impaired mucosal barrier
      1. => Mucosal barrier is disrupted -> Pepsin & acid cause Necrosis -> Erosion/ulcers (Erosion of underlying blood vessels -> Haemorrhage
    2. Causes:
      1. NSAIDs
        Corticosteroids (Stress)
        Viral infection (e.g. mucosal disease)
        Foreign bodies
        Intestinal obstruction (reflux of bile)
        Neoplasia
        Idiopathic
        (Local Trauma)
        (Local Ischaemia)
  2. Dogs: NSAIDs, Mast cell tumor (Histamine => HCl hypersecretion), Pancreatic gastrinoma (Tumor derived from Islets -Pancreas -> Gastrin) Azotaemia, Cirrhosis, Bile reflux
  3. Pigs (weaned growers & feeders): Finely ground grain concentrate diets - stratified squamous areas of stomach affected
  4. Horses: Stress/ NSAIDs - stratified squamous epithelium at margo plicatus (adults & foals), glandular area (foals)
  5. Cattle: Periparturient lactic acidosis, Abomasal impaction, displacement or torsion, Mucosal disease - Bleed & perforation
  6. Heal by granulation & fibrosis or perforate
4. Neoplasia
  1. Adenocarcinoma
    1. Malignancy of mucosal epithelium
    2. Most common gastric neoplasm in Small animals
    3. Locally aggressive & spreads via lymphatic vessels to lymph nodes, lung, liver
    4. Thickened, pale tissue, ulcerated of fungating
  2. Squamous cell carcinoma
    1. Commonest gastric tumor in Horses
    2. Large cauliflower-like mass
      1. Metastases & transcoelomic spread
  3. Leiomyoma/Leiomyosarcoma
    1. Smooth muscle neoplasms forming nodular masses
    2. Mainly Dogs
  4. Lymphoma
    1. Diffuse infiltration of Neoplastic lymphocytes
    2. Dogs, Cats, Horses

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Pathology of Alimentary Tract 2 (Ruminant Forestomachs/ Glandular stomach)

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