Respiratory Pathology

Routes of Invasion
1. 1) Aerogenous
  1. Trachea: High speed
    1. Bronchi/bronchioles: Slower speed
      1. => Aerogenous particles settle (Cranioventral areas)
  2. Cranial & Medial lobes
2. 2) Haemotogenous
  1. Random scattering of multifocal lesions
    1. Ex. Metastases
3. 3) Transcoelomic
  1. Ex. Traumatic Reticulitis (Entry through Diaphragm)
Nasal Cavity
1. Normal flora:
  1. Variable (Gram +ve)
    1. Prevent adherence by pathogenic (often Gram -ve bacteria)
2. Circulatory Problems
  1. Epistaxis
  2. Ex. Equine Ethmoid Haematoma
    1. Chronic nasal bleeding
      1. Old horses
        Pedunculated mass in ethmoidal region
        Expansive, but non-neoplastic
        Progressive Ethmoid Haematoma (PEH)
        Gets bigger over time
3. Rhinitis
  1. Infectious (Upper Resp. tract infections)
    1. Viruses
      1. Bacteria
        Fungi
        Ex. Aspergillus fumigatus
        Chronic necrotizing inflammation => destruction of turbinates & septum
        Cryptococcus neoformans
        Nasal cavity often affected
        Sneezing, nasal discharge, nasal swelling (Granulomatous rhinitis)
        +/- Skin, ocular & CNS lesions
        Has a thick, non-staining mucoid capsule
        Ex. Atrophic rhinitis
        Strangles (Streptococcus equi)
        Lymphadentitis, Pharyngitis, Rhinitis, Metastatic abcesses, Guttural pouch empyema, Purpura haemorrhagica
      2. Ex. Feline viral rhinotracheitis, Canine distemper, Infectious Bovine Rhinotracheitis, Equine Rhinovirus
  2. Allergens
  3. Toxins
  4. Trauma/foreign bodies
  5. Classification
    1. Serous
      1. Catharral
        Mucopurulent
        Purulent
        Fibrinous
        Ulcerative
        + Fibrinonecrotic => Full thickness of epithelium exposed
        Fibrin deposits
        Overproduction of Mucous (Goblet cells) + Neutrophil Infiltration => Snotty nose
        Overproduction of mucous by Goblet cells
      2. Overproduction of Serous fluid (by Serous cells)
  6. Chronic Rhinitis
    1. Consequence of Acute Rhinitis failing to resolve
    2. Chronic purulent rhinitis
    3. Nasal Polyps
  7. Allergic Rhinitis
    1. Hypersensitivity to inhaled allergens
    2. Nasal epithelium damaged by cytokines
      1. Succeptible to 2ndary bacterial infections
        Eosinophils often the dominant infiltrating leukocyte
4. Pseudostratified columnar epithelium
5. Sinusitis
  1. Common sequel to Rhinitis
  2. Close proximity of sinuses to nasal cavity (Blockage of sinus drainage)
  3. Purulent inflammation of the sinuses -> Chronic (poor drainage)
  4. Dental or peridontal disease (maxillary sinus)
    1. Penetration of infections from dehorning wounds & fractures of the facial bones (Frontal sinus)
6. Neoplasia (Nasal Cavity & Sinuses)
  1. Generally rare (more common in Dogs)
  2. Can arise from any of the tissues in the region
    1. Adenoma/carcinoma (Glands/epthelium)
      1. Sarcoma (Cartilage, bone, connective tissue)
  3. Most are malignant & are usually 2ndarily infected
  4. Ex. Endemic ethmoid tumors (Ruminants): Retroviral origin - Carcinomas
Conducting Airways
1. Larynx & Trachea
  1. Airflow obstruction
  2. Aspiration pneumonia
  3. Necrotic Laryngitis
    1. Ex. Calves: Fusobacterium necrophorum
      1. Friable appearance
    2. Cranial /Ventral lung lobes
      1. Massive inflammatory rxn (rupture onto surface)
  4. Laryngeal Chondritis
    1. Texels & Southdowns (Other breeds)
    2. Rams > Ewes
    3. Chronic suppuration w/in the arytenoid cartilages of the larynx resulting in swelling & occlusion of the lumen (of larynx)
  5. Filaroides Osleri
    1. Parasite (Canine)
    2. Nodules around tracheal bifurcation
    3. Foreign body nodular rxn develops around dead parasites
  6. Tracheitis
    1. Thickening, hyperplasia of lamina propria
      1. 2ndary bacterial infections
        Clumps of necrotizing debris
    2. Runny nose, runny eyes
    3. High morbidity, low mortality
    4. Ex. Infectious Bovine Rhinotracheitis
  7. Non-inflammatory Tracheal Diseases
    1. Tracheal Collapse
      1. Dorsoventral tracheal flattening
        Tracheal ligament has become stretched
        Older, small breed dogs
    2. Tracheal Neoplasia (Uncommon)
2. Bronchi
  1. Bronchitis
    1. Acute
    2. Chronic
      1. Goblet cell hyperplasia & hypersecretion
        Squamous metaplasia
        Bronchiectasis
        Permanent dilation of bronchi (as a result of accumulation of purulent exudate in the lumen)
        Partial rupture of bronchial walls (irreversible)
        Usually 2ndary to chronic bronchitis
        Grape bunch appearance
      2. Dogs:
        Chronic cough
        Excess airway exudate
        Thickened mucosa
        Chronic inflammation
        => Stimulation of muscular hypertrophy in walls of small arteries
        Pulmonary hypertension => Cor pulmonale (RT heart failure)
  2. Infectious tracheobronchitis (Kennel Cough)
    1. Common
    2. Persistent tracheobronchial inflammation
      1. If severe => Rhinitis or Bronchopneumonia
    3. Bordetella bronchiseptica
      1. PI2
        CAV2
  3. Bronchioles
    1. Epithelium highly susceptible to injury:
      1. Presence of Clara cells (contain oxidases that can locally generate metabolites that are toxic)
        Vulnerability to free radical damage
    2. Bronchiolitis
      1. Bronchiolar Obstruction
        Bronchioles much more prone to obstruct when inflamed than Bronchi
        Not much cartilage (rigid structure) -> Fills w/ inflammatory cells
        Where collateral ventilation is poor (Ruminants) obstructed bronchiole -> Atelectasis
      2. Extension of or concurrently w/ Bronchitis & Pneumonia
      3. Certain viral infections (pulmonary toxicity)
      4. When exudate cannot be cleared -> infiltration by fibroblasts -> development of organized polyp-like masses w/in the bronchiolar lumen => Bronchiolitis Obliterans
Alveoli
1. Structure
  1. Simple squamous epithelium
    1. Type 1 Pneumocytes: Flattened, fried egg, cover 97% of septal surface
    2. Type 2 Pneumocytes: Cuboidal, cover approx. 3% of septal surface
      1. Produce Surfactant
      2. Progenitor of Type I & Type II Pneumocytes
        Repair surface of lungs (Damage)
2. Response to Injury
  1. Aveolar Epithelialisation
    1. Marked lung damage (Type II Pneumocytes predominate)
  2. Hyaline Membrane Formation
    1. Severe & Acute lung disease
    2. Stain pink
3. Pneumonia
  1. Consolidation = altered texture of lung (firmer) due to accumulation of exudates (fluid & cellular infiltrate)
  2. Inflammation that takes places in the alveoli & their walls
  3. Classification via:
    1. Nature of inflammatory process
      1. Aetiological agent
        Pattern
  4. Bronchopneumonia
    1. From terminal bronchioles
      1. Aerogenous portal of entry => Cranioventral
    2. Common (Bacterial, Mycoplasmal)
    3. Neutrophils & cell debris =>
      1. Sequella:
        Resolution (mucociliary escalator, resolves 3 -4 weeks)
        Progression => Chronic Suppurative Bronopneumonia
        Consequences:
        Bronchiectasis
        Pulmonary abcessation
        Pleuritis & adhesions
        Atelectasis or overinflation
        BALT hyperplasia
    4. Fibrinous Bronchopneumonia
      1. Acute (tends to be more severe than suppurative)
      2. => Sudden death (possible) - toxaemia (Pasteurella)
      3. => Fibrosis & adhesions (b/w visceral & parietal pleura)
    5. Bronchointerstitial Pneumonia
      1. Hybrid of Bronchopneumonia & Interstitial Pneumonia
      2. Caused by viruses damaging both airway & alveolar epithelial cells (Ex. RSV)
  5. Interstitial Pneumonia
    1. Inflammation primarily in alveolar walls
    2. Haematogenous spread (Most cases)
      1. Diffuse damage
    3. (May)=> Protein & fluid exudation => Hyaline membrane formation
    4. Exudative phase followed by proliferative phase (Type II pneumocytes proliferate to replace damaged Type I cells)
    5. Acute
      1. May be transient (Ex. viral infections)
      2. May be severe & associated with life threatening pulmonary oedema (Ex. Acute Resp. distress syndrome -ARDS)
      3. Examples:
        Fog Fever (Acute Bovine Pulmonary Oedema & Emphysema)
        Adult beef cattle
        Autumn (change to lush pasture)
        Ingestion of Tryptophan (3 methyl indole) in rumen
        Local generation of Free Radicals => Necrosis of Type I Pneumocytes
        Hyaline formation => Acute interstitial Pneumonia => Chronic Interstitial Pneumonia
        Paraquat Poisoning
        Weed killer (uncommon)
        Dogs & Cats
        Acute & Chronic lesions
        Extrapulmonary lesions
        Necrosis of adrenal zona glomerulosa
        Necrosis of Renal tubular epithelium
    6. Chronic
      1. Dominated by fibrosis of alveolar walls & proliferation of Type II Pneumocytes
  6. Embolic Pneumonia
    1. Haematogenous spread
    2. Most often Caudal (Can occur anywhere)
      1. B/c more lung tissue
    3. Oriented around blood vessels (Embolis must come in vascular supply)
  7. Granulomatous Pneumonia
    1. Dominated by macrophages, +/- giant cells
    2. Varying associated lymphocytes & neutrophils
    3. Multiple granulomas scattered throughout the lungs
  8. Pulmonary Abscesses
    1. 1) Extension from Pneumonia
    2. 2) Septic emboli
      1. Ex. Suppurative mastitis
    3. 3) Aspiration of foreign material
    4. 4) Direct penetration
      1. Ex. Traumatic reticulocarditis
  9. Enzootic Pneumonia
    1. Young animals in close contact (Calves, Lambs & Pigs)
  10. Parasitic Disease
    1. Dictyocaulus viviparus
      1. Lifecycle
        Penetration phase
        In transit
        Prepatent phase
        Sequential alveolitis -> bronchiolitis -> bronchitis
        Patent Phase
        Parasitic bronchitis & pneumonia
        Postpatent Phase recovery
        Acute signs due to:
        Alveolar epithelialisation
        Superimposed infection
      2. Wedge-shaped lesions
    2. Dictyocaulus filaira
    3. Dictyocaulus arnfeldi
      1. Common (rarely clinical disease)
      2. Horses & Donkeys
      3. Gross pathology
        Raised focal over-inflated areas in the caudal lung lobes
      4. Histology
        Central parasites & associated chronic catharral bronchitis
        Hyperplastic bronchial epithelium & surrounding lymphoid infiltration
    4. Metastrongylus (Pigs)
    5. Muellerius capillaris
      1. Common (rarely clinical sig.)
      2. Firm "lead shot" nodules
      3. Dorsal regions of caudal lobes
    6. Aerostrongylus abstrusus
      1. Cat lungworm
      2. Firm, yellow nodules in parenchyma
      3. Eggs & larvae -> Foreign body type Rxn
      4. Chronic coughing & airway Eosinophilia (can resemble asthma)
    7. Angiostrongylus vasorum (Heart worm)
      1. Pulmonary arteries & RT ventricle
      2. Dogs & Foxes
      3. Can cause proliferative change in blood vessels => Pneumonia => Pulmonary Oedema & Hypertension
    8. Echinococcus granulosus
      1. Intermediate stage (Lungs)
      2. Little clinical significance
        Zoonosis & carcass condemnation
        Hydatid Cyst
    9. Hypersensitivity Diseases
      1. Type I Hypersensitivity
        Mast cell mediated (Through Ag- IgE complexes)
        => Degranulation
        Constriction of airways
        Feline Asthma/ Allergic Bronchitis
        Inhaled Ags
        Recurrent episodes of bronchoconstriction
        Inflammation (Eosinophil dominated)
        +/- Circulating Eosinophilia
        Pulmonary Infiltration w/ Eosinophilia
        Dog
        Predominance of Eosinophils in airways
        Inhaled Ags
      2. Type III Hypersensitivity
        Ag-Ab Complex mediated
        Can settle in alveolar blood vessels
        Extrinsic Allergic Bronchio-alveolitis
        Repeat inhalation of spores
        Chronic inflammation
        Thickening of alveolar septae
        Housed Dairy Cows (Winter)
        Diffuse Fibrosing Alveolitis (DFA)
        COPD - Chronic Obstructive Pulmonary Disease (SPAOPD -Summer pasture associated)
        Chronic coughing, poor performance
        Airway inflammation, excess mucus
        Heaves (Heave line)
        Gross:
        Affected lungs unremarkable (except in extreme cases - alveolar emphysema)
        Histologically:
        Chronic generalized bronchitis
        Plugging of airways w/ mucous, inflammatory cells, goblet cell metaplasia & smooth muscle hypertrophy
  11. Aspiration Pneumonia
    1. Inhaling foreign particle
    2. Severity depends on nature of material (ex. food), bacterial load, & distribution w/in lungs
    3. Can develop into Severe Necrotizing pneumonia => Gangrenous pneumonia
      1. Abscesses
  12. Gangrenous Pneumonia
    1. Tissue becomes necrotic -> invaded by putrefactive saphrophytes (Ex. Clostrdia)
      1. Dead tissue undergoes Liquefactive Necrosis
    2. Usually Iatrogenic or as a sequel to aspiration pneumonia
  13. Lipid Pneumonia
    1. Endogenous
      1. Cats > Dogs
      2. Subclinical
      3. Accumulation of lipids (surfactant) in pulmonary macrophages -> multifocal white nodules
    2. Exogenous
      1. Associated w/ inhalation of oil, paraffin, etc.
      2. Rxn dominated by macrophages which fill the alveoli
      3. Interstitial thickening (mononuclear cells & fibrosis) - Inflammation
  14. Uraemic Pneumonia
    1. Sever uraemia => increased permeability of the blood -air barrier
    2. (May) => Pulmonary Oedema
    3. (May) => Degeneration & calcification of smooth muscle & connective tissue
Pulmonary Oedema
1. Protection Mechanisms
  1. Impermeable epithelium & junctions
    1. Interstitial pressure in alveolar septae lower than intraalveolar pressure
      1. Efficient lymphatic drainage
      2. Pushes fluid out of alveoli
2. Excessive fluid in the lung
3. Begins as Interstitial Oedema
  1. Expansion of perivascular, peribronchial & peribronchiolar fascia & distension of interstitial lymphatics
  2. Interstitial compartment overwhemled => fluid floods airspces => Alveolar oedema
4. Causes
  1. Increased capillary or Type I epithelial permeability
    1. Systemic toxins
    2. Shock
    3. Inhaled caustic gases
  2. Increased capillary hydrostatic pressure (cardiogenic oedema)
    1. LT sided or Biventricular Heart failure
    2. Increased hydrostatic pressure -> pushes fluid into lungs
  3. Decreased plasma oncotic pressure (Hypoalbuminaemia)
    1. Proteins keep fluid in plasma (Decreased proteins -> fluid leaves vascular compartment -> Lungs)
Pulmonary Haemorrhage
Embolism, Thrombosis & Infarction
1. Lung supplied by BOTH Pulmonary & Bronchial Arteries
  1. Infarction doen NOT usually follow embolism or thrombosis, UNLESS pulmonary circulation is already compromised
    1. Usually occur w/ emboli/thrombosis during general circulatory collapse or passive congestion of heart failure
Pulmonary Hypertension
1. Caused by LT -> RT vascular shunts or Increased resistance of the pulmonary vascular system
2. Most commonly a sequel of:
  1. Widespread fibrosis in the lung
    1. Chronic bronchitis or bronchiolitis (stimulates hypertrophy in the walls of small arteries)
3. Severe, Prolonged => Cor Pulmonale
  1. RT-sided Heart failure 2ndary to primary lung disease
Neoplasia
1. Pulmonary Tumors
  1. Metastatic: Common
    1. OPA (Ovine Pulmonary Carcinoma)/ Jaagsiekte
      1. Retrovirus induced cancer
      2. Intensive management systems - Aerosol transmission
      3. 'Wheelbarrow test'
      4. Well differentiated carcinoma
      5. Can get dry forms of OPA (cells not so active in producing surfactant)
  2. Primary: Relatively Rare
    1. Dogs & Cats
2. Bronchial papilloma
3. Bronchial adenoma/carcinoma
  1. Arising from major airways
4. Bronchioloalveolar adenoma/carcinoma
  1. Arising from small airways or alveolar parenchyma (either secretory bronchiolar cells or Type II epithelial cells)
  2. Carcinoid
    1. Neuroendocrine cells (Rare in animals)
5. Mesothelioma
  1. Most common in Calves (can be congenital)
  2. Often causes Thoracic effusion
  3. Multiple nodular masses on pleural surface & visceral surface
  4. Dx can be difficult due to cytological similarity of reactive & neoplastic mesothelial cells

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Respiratory Pathology

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	Created by melian.yates over 10 years ago