Hemorrhagic infarction is always pyramidal in shape with its base at the surface and apex directed inward. It varies in size but is sharply circumscribed, dense, dark-red in color, and projects under the pleura above the surrounding tissue. Its borders coincide accurately with those of the lobules, never limited to a portion of a lobule. On section, it appears very dark-red or almost black, distinguished by its clearly defined pyramidal shape, smooth surface from which fluid blood can be scraped, great density, and localization at the periphery. A plugged artery is often found at the center — secondary thrombosis. Microscopic examination reveals alveoli filled with coagulated blood, capillaries compressed and empty. Subsequent changes involve purulent circumscribed inflammation separating the affected portion from surrounding parts. The softened mass is surrounded by a narrow yellow line limited by a zone of redness gradually disappearing toward the periphery. Progressive suppuration may detach the mass into a cavity that cicatrizes and heals, or decomposition sets up gangrene with greenish-brown fluid in cavities lined by shreds of pulmonary tissue. Pleurisy often accompanies such conditions.
Embolism infarction results from plugging of a branch of the pulmonary artery, resembling hemorrhagic variety but not sharply defined; it merges gradually into healthy tissue and is seldom large due to partial plugging of larger branches being rapidly fatal or leading to no infarction. Embolic infarctions occur only with bland thrombus exerting purely mechanical influence; septic material leads to small abscesses (embolic pneumonia), sometimes alone present, occupying periphery or center of lung indifferently.
Inflammation forms include fibrinous and cellular types. Fibrinous pneumonia affects whole lobes diffusely, progressing through stages from engorgement to resolution with gradual density reduction, granular character loss, and yellow coloration. Microscopic examination reveals fatty degenerated cells and viscid fluid into which fibrine has been converted; cavities may arise due to disorganization.
Cellular pneumonia includes catarrhal (broncho-pneumonia) and cheesy forms. Catarrhal pneumonia is lobular with small gray or grayish-yellow spots in reddened lung substance, progressing uniformly in later stages. Chronic form is common, characterized by oedema, grayish color, minute light yellow spots, highly albuminous fluid.
Cheesy pneumonia progresses through red to yellow stages, dry cut surface, density, and finely granular appearance; alveolar contents consist of large epithelioid cells closely aggregated together — old and young desquamated epithelium. Metastatic pneumonia occurs as multiple peripheral nodules beneath pleura, often terminating in abscesses with septic or malignant character leading to foul exudation.
<Callout type="important" title="Critical Identification">Hemorrhagic infarction is distinguished by its pyramidal shape and sharply defined borders, while embolic infarctions are less distinct and merge into healthy tissue.</Callout>
Fibrinous pneumonia progresses through stages with characteristic changes in color and consistency. Cellular forms include catarrhal and cheesy types, each with unique microscopic features and progression patterns.
<Callout type="warning" title="Dangerous Decomposition">Decomposition can set up gangrene leading to cavities filled with greenish-brown fluid, lined by shreds of pulmonary tissue.</Callout>
Metastatic pneumonia often results in abscesses with septic or malignant character, setting up inflammation and foul exudation.
Key Takeaways
- Hemorrhagic and embolic infarctions have distinct characteristics for identification.
- Fibrinous pneumonia progresses through stages with specific microscopic features.
- Cellular forms of pneumonia include catarrhal and cheesy types, each with unique patterns.
Practical Tips
- Identify hemorrhagic infarction by its pyramidal shape and sharply defined borders.
- Recognize fibrinous pneumonia's progression from red to yellow stages.
- Differentiate cellular forms based on microscopic features of alveolar contents.
Warnings & Risks
- Decomposition can lead to gangrene with cavities filled with greenish-brown fluid.
- Metastatic pneumonia often results in abscesses with septic or malignant character.
Modern Application
While the detailed anatomical descriptions are foundational, modern medical imaging and diagnostic techniques have advanced triage capabilities. However, understanding these historical classifications remains crucial for accurate diagnosis and treatment planning in emergency settings.
Frequently Asked Questions
Q: What distinguishes hemorrhagic infarction from embolic infarction?
Hemorrhagic infarction is sharply defined with a pyramidal shape, while embolic infarctions are less distinct and merge gradually into healthy tissue.
Q: How does fibrinous pneumonia progress through stages?
Fibrinous pneumonia progresses from engorgement to resolution, characterized by changes in color (red to yellow) and consistency, with density reduction and granular character loss.
Q: What are the microscopic features of cheesy pneumonia?
Cheesy pneumonia's alveolar contents consist of large epithelioid cells closely aggregated together — old and young desquamated epithelium, progressing through red to yellow stages with dry cut surface and finely granular appearance.