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

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

1. Ruminant Forestomachs

   • Forestomachs: Rumen, Reticulum, Omasum
   • Note: Postmortem putrfactive changes occur rapidly (Gas distension, Sloughing of mucosa)
   • Functional Disorders
     • Bloat (Ruminal Tympany)
       • Failure to expel fermentation gases
       • Pathogenesis:
         • 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
         • 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)
       • Overdistension of Rumen & Reticulum with fermentative gases
         • 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
     • Runminal Acidosis (Grain overload)
       • Ruminitis may develop => allow thromboemboli to travel to the Liver => Hepatic abcessation
         • 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)
   • Inflammation
     • Traumatic Reticulitis "Hardware disease"
       • Ingestion of sharp objects (e.g. wire, nails)
       • 1) Fall to floor or reticulum => Insignificant
       • 2) Contractions force foreign body into wall of reticulum:
         • => Mild suppurative or Granulomatous reticulitis +/- Peritonitis
           • Localized => Adhesions
       • 3) Foreign body penetrates Cranial wall (rumen contractions) :
         • => Acute Peritonitis, Local Fibrous adhesions
           • => Penetrates Diaphragm (Fibrinopurelent pleurisy, pneumonia, pericarditis)
             • Fusobacterium, Actinomyces spp.
       • Inflammatory process around Reticulum (may) => vagus indeigestion & ruminal stasis
       • => Purulent fluid build up => Cardiac Failure
     • Ruminitis (Bacterial or Mycotic)
       • Bacterial
         • Lactic Acidosis
           • Opportunistic pathogens (Take advantage of acidotic lesions & other disturbances of rumen flora)
         • Mechanical Injury to Rumen
           • Ex. Traumatic Reticuloperitinitis
           • Damage to Rumen wall => Infiltration of bacteria (GI colonizers)
         • Fusobacterium necrophorum, Trueperella pyogenes, Actinobacillus lignieresii
       • Mycotic
         • Abx, Lactic Acidosis
         • Vascular invasion -> Thrombosis -> Infarction
         • Haematogenous -> Placentitis -> Abortion
         • Mucor/Rhizopus/Absidia
       • Gross: Multiple, dark red areas of swollen paillae, Coagulative necrosis of papillae, Serofibrinous exudate
       • Histologically: Coagulative necrosis of papillae, marked neutrophil infiltrate
       • Thromboembolic spread => Form areas of coagulative necrosis & abscesses in Liver
   • Neoplasia
     • Papillomatosis
       • Bovine papillomavirus type 4
       • Usually pedunculated structures in Reticulum/Rumen of Cattle
     • Squamous cell carcinoma
       • Thought to develop from papillomas in Cattle in association with ingested carcinogens in Bracken Fern

2. Pathology of the Glandular Stomach & Abomasum

   • Physical Disturbances
     • Obstruction
       • Foreign body
         • Bones, stones, hair/wool balls (trichobezoars), plant material (phytobezoars)
       • Pyloric Stenosis
         • Dogs, Foals, Cats
         • Congenital Hypertrophy of Pyloric muscle
           • => Delayed Gastric emptying & persistent vomiting/regurgitation
         • Acquired
           • Following healed ulcers (foals)
       • Functional Obstruction
         • Dysautonomia
           • Feline dysautonomia
           • Equine Grass sickness
         • Vagal indigestion (Cattle)
         • End-stage liver disease (Equine)
       • Horses DON'T vomit! Stomach will rupture before they vomit
     • Displacements of the stomach/abomasum
       • Herniation of Stomach (through diaphragm)
         • Congenital (Cats)
           • Often associated w/ herniation of Liver
             • Peritoneo-pericardial diaphragmatic hernia
         • Acquired (Dogs, Cats)
           • RTAs
             • Displacement of GI tract into peritoneal cavity
       • Abomasal Displacement (Cattle)
         • Ventral & to left of Rumen (LDA)
           • 85% of Displacements
           • Partial obstruction of outflow
             • Mild consequences: May not require surgery
         • To right of Rumen (RDA)
           • 15% of Displacements
           • Acute dilation & volvulus
             • Severe consequences: Usually require surgery
             • Obstructs outflow from abomasum
         • Normal location: Close to or just right of the ventral midline
         • 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
         • Predisposing factors:
           • Post-parturient Dairy Cows
             • Change to grain concentrates in diet (Increased VFAs -> Affect motility)
               • Hypocalcaemia (Abomasal atony)
   • Inflammation
     • Haemorrhagic/necrotizing Abomasitis
       • Braxy
         • Sheep/Cattle
         • 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
         • Clostridium septicum (Exotoxin)
     • Bacterial Gastritis & Gastric Ulceration
       • Heliobacteriosis
         • Dogs, Cats
         • Helicobacter heilmannii, Helicobacter felis
         • Chronic mucoid gastritis
     • Hypertrophic Gastritis/ Abomastitis
       • Chronic hypertrophic gastritis (Dogs)
         • Chronic retention of gastric fluid & bile reflux
         • 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
       • Parasitic Gastritis (Osteragiosis)
         • Cattle: Ostertagia ostertagi
           • Sheep: Teladorsagia circumcincta
         • Acute Gastritis
           • Hyperaemia & oedema
         • Chronic Gastritis
           • Nodules (encysted larvae) in abomasal mucosa, "Morocco leather" appearence
         • Glandular hyperplasia, loss of parietal/chief cells, chronic inflammation associated w/ lymphocytes, plasma cells & eosinophils & larvae
     • Chronic Atrophic Gastritis (Dogs)
       • Aetiology uncertain
         • Mucosal thinning & loss of gastric glands, diffuse mixed inflammtory infiltrate in the lamina propria
   • Ulceration
     • Pathogenesis
       • Hypersecretion of acid &/or impaired mucosal barrier
         • => Mucosal barrier is disrupted -> Pepsin & acid cause Necrosis -> Erosion/ulcers (Erosion of underlying blood vessels -> Haemorrhage
       • Causes:
         • NSAIDs
           • Corticosteroids (Stress)
             • Viral infection (e.g. mucosal disease)
               • Foreign bodies
                 • Intestinal obstruction (reflux of bile)
                   • Neoplasia
                     • Idiopathic
                       • (Local Trauma)
                         • (Local Ischaemia)
     • Dogs: NSAIDs, Mast cell tumor (Histamine => HCl hypersecretion), Pancreatic gastrinoma (Tumor derived from Islets -Pancreas -> Gastrin) Azotaemia, Cirrhosis, Bile reflux
     • Pigs (weaned growers & feeders): Finely ground grain concentrate diets - stratified squamous areas of stomach affected
     • Horses: Stress/ NSAIDs - stratified squamous epithelium at margo plicatus (adults & foals), glandular area (foals)
     • Cattle: Periparturient lactic acidosis, Abomasal impaction, displacement or torsion, Mucosal disease - Bleed & perforation
     • Heal by granulation & fibrosis or perforate
   • Neoplasia
     • Adenocarcinoma
       • Malignancy of mucosal epithelium
       • Most common gastric neoplasm in Small animals
       • Locally aggressive & spreads via lymphatic vessels to lymph nodes, lung, liver
       • Thickened, pale tissue, ulcerated of fungating
     • Squamous cell carcinoma
       • Commonest gastric tumor in Horses
       • Large cauliflower-like mass
         • Metastases & transcoelomic spread
     • Leiomyoma/Leiomyosarcoma
       • Smooth muscle neoplasms forming nodular masses
       • Mainly Dogs
     • Lymphoma
       • Diffuse infiltration of Neoplastic lymphocytes
       • Dogs, Cats, Horses

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