Pneumonia

• It is defined as the inflammation of lungs, with copious exudate filling the alveoli.

Routes of Infection:
1. Respiratory passage (Bronchogenous)
2. Blood
3. Exterior (Penetrating wounds through abdominal cavity, reaching diaphragm → lung)

Etiology:
• Physical irritants, chemical irritants
• Parasites
• Bacteria (Respiratory as well as Blood)

Stages of pneumonia
1. Stage of Congestion:
• Description: This is the initial stage of pneumonia, where there is inflammation and
blood flow increases to the affected area (hyperemia). Fluid leaks into the alveoli (small air sacs
in the lungs), causing edema (swelling).
• Macroscopic Appearance: The lungs appear heavy, red, and swollen.
• Microscopic Appearance: Under a microscope, the alveolar walls are dilated (enlarged)
and filled with blood. The alveoli contain serous (clear) exudate along with a few red blood cells.
2. Stage of Red Hepatization:
• Description: In this stage, the lungs take on a liver-like appearance, hence the term
“hepatization.” The alveoli are filled with red blood cells, white blood cells, and fibrin (a protein
involved in blood clotting), making the affected lung tissue solid.
• Macroscopic Appearance: The affected lung tissue is red, solid, and resembles liver
tissue.
• Characteristics: The affected part is airless and shows a line of demarcation (a visible
boundary) between infected and healthy lung tissue.
3.Stage of Grey Hepatization :
• Definition: This stage follows red hepatization and is characterized by a grey or
yellowish appearance of the lung tissue, as the red blood cells begin to break down.
• Microscopic Details (from image): The alveolus is less filled than the previous stage.
The presence of fibrin, hemosiderin, and breakdown of RBCs leads to a more fluid-like exudate.
These details are highlighted in green and blue ink.
4.. Stage of Resolution (

• Definition: This is the final healing phase, where the exudate begins to clear from the
alveoli, restoring the lung tissue.
• Microscopic Details (from image): Liquefaction and removal of exudate occur, and the
liquefied material may be absorbed through lymphatics or veins or expelled. Microscopically,
exudate disappears and appears granular (terms highlighted in green and orange ink).

Types of Pneumonia: Bronchopneumonia

1. Bronchopneumonia

• Definition: It is the inflammation of lungs involving bronchi or bronchioles along with

alveoli.
• Characteristics: It is characterized by cranioventral consolidation of the lungs.

Etiology

1. Bacteria
2. Viruses
3. Mycoplasmas
4. Fungi
5. Parasites
6. Chemical agents
7. Foreign particles
 • Route of Infection: Infection is mainly through the bronchogenous route.

Pathogenesis

• Before establishing, the pathogens must either overcome or avoid the pulmonary
defense mechanism.
• The first injury occurs in the mucosa of bronchioles and alveoli.
• From here, the inflammatory process can spread downward to distant portions of
alveoli and upward to the bronchi.
• In Bronchopneumonia: The inflammatory exudate collects in the bronchioles and
alveolar lumina, leaving the alveolar interstitium unaffected.
• Spread Mechanism: Through pores of Kohn, the lesions spread to the neighboring
alveoli until all the alveoli in a lobule are involved.
• The inflammatory lesions spread rapidly from lobule to lobule through alveolar pores to
the damaged alveolar walls, until an entire lobe of the lung is involved.

Types of Bronchopneumonia

A. Suppurative Bronchopneumonia

• Definition: Characterized by the presence of purulent or mucopurulent exudate in the

airways and cranioventral consolidation of lungs.
• Inflammation: The inflammation is usually confined to individual lobules. As a result,
the lobular pattern becomes prominent.
• Causes:
• Pasteurella multocida
• Streptococcus spp.
• Bordetella bronchiseptica
• Gross Appearance: The lung presents an alternate pattern of colors (checkerboard
appearance) due to a mix of normal and abnormal lobules.
• Microscopically: There is excessive infiltration of neutrophils and macrophages.
B. Fibrinous Bronchopneumonia

• Definition: If fibrin is the main component of exudate, it is called fibrinous

bronchopneumonia.
• Characteristics: It also has cranioventral distribution, but the exudation is not confined
to the boundaries of individual lobules. Instead, the inflammatory process involves many
adjacent lobules.
• The exudate moves quickly through lung tissue until the entire lobe is affected. It
results in a more severe condition, endangering life.
• Gross Appearance:
• Early Stages: Lung is characterized by severe congestion and hemorrhage, giving it a
red color.
• After a few hours: Fibrin also accumulates on the surface and can give a yellow
appearance (only fibrin), yellowish-brown (fibrin + blood), gray (leukocytes also), resulting in a
marbled appearance.
• Microscopically: There is massive leakage of plasma proteins into the bronchioles and
alveoli. As a result, air spaces are destroyed by fluid and fibrin.

Here is a more structured version of the notes based on the images you provided:

Types of Pneumonia

1. Interstitial Pneumonia

• Definition: A special type of pneumonia characterized by inflammation occurring mainly

in the interstitial areas of the lungs, including the alveolar walls (endothelium, basement
membrane, alveolar epithelium) and adjacent bronchioles.
• Etiology:
1. Damage to alveolar endothelium:
• Caused by inhalation of toxic gases, fumes (e.g., smoke), or viral infections.
• Results in the release of toxic metabolites and free radicals.
2. Vascular endothelium injury:
 2. Vascular endothelium injury:
• Occurs in septicemias or absorption of toxins into the alimentary canal, leading to
bacterial diseases.
3. Inhaled antigens (e.g., fungal spores):
• Combine with circulating antibodies, forming antigen-antibody complexes in alveolar
walls.
• Pathophysiology:
• These factors initiate inflammation, damaging the alveolar wall and capillary
endothelium, causing fibrous exudate in the alveolar septa.
• Increases permeability in alveolar walls, affecting oxygen transfer, leading to hypoxia
and edema in septa.
• Gross Characteristics:
• Lungs do not collapse upon opening of the thorax.
• Color varies from red to pale gray.
• Surface shows visible exudation.
• Secondary bacterial infection may complicate it.
• Consistency of lung is elastic.
• Microscopic Features:
• Alveolar walls and interlobular septa thickened by exudate (serous or fibrinous).
• Interstitial infiltration by neutrophils, lymphocytes, and macrophages.

2. Embolic Pneumonia

• Definition: Characterized by multifocal lesions distributed across pulmonary lobes,

caused by septic emboli.
• Etiology:
• Occurs when septic emboli are trapped in pulmonary vessels, especially alveolar
capillaries, spreading infection to the lung interstitium.
• Gross Characteristics:
• Lungs exhibit numerous small, white foci surrounded by red areas, indicating infection
sites.

3. Granulomatous Pneumonia
 • Definition: Characterized by caseous or non-caseous granulomas in the lungs.
• Etiology:
• Pathogens enter the lungs through airborne particles or bloodstream.
• Pathogens causing this pneumonia are resistant to intracellular killing by phagocytes,
triggering an acute inflammatory response.
• Persistence of pathogens in tissues over extended periods.
• Gross Characteristics:
• On palpation, lungs show a nodular appearance due to granulomatous lesions.
Micro.: Granulomas are composed of a centre of necrotic tissue surrounded by a rim of
macrophages and gaint cells

Mycotic Pneumonia

• Definition: Infection of the lung caused by a variety of fungi, often associated with
Aspergillus fumigatus.
• Commonly Affected Animals: Birds (especially brooder pneumonia) and animals
undergoing prolonged antibiotic therapy.
• Pathogenesis:
1. Spores Entry: Spores enter terminal bronchioles and alveoli.
2. Growth: Spores grow by budding and form septate hyphae.
3. Inflammatory Response: Local inflammation occurs, leading to nodular
bronchopneumonia.
4. Infiltration: The affected area is infiltrated by polymorphs and macrophages.
5. Expansion: The focus expands, involving more lung tissue.
• Gross Findings:
• Lesions: Lungs show nodular lesions.
• Air Sacs: Thickened air sacs may exhibit fungal growth.
• Microscopic Findings:
• Hyphae: Septate hyphae of fungi with inflammatory cells are seen around a central
necrotic area.

Aspiration Pneumonia
 • Definition: Pneumonia caused by the inhalation of foreign materials, such as food or
liquids, into the lungs.

Metastatic Suppurative Pneumonia

• Also Known As: Embolic Pneumonia.

• Lesions: Commonly observed in diaphragmatic lobes.