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  1. Lobar pneumonia refers to consolidation of an entire lobe while bronchopneumonia is scattered solid foci in the same or several lobes. 

Bacterial pneumonias occur in three settings:

  1. Community-acquired pneumonia arises outside the hospital.
  2. Nosocomial pneumonia represents an infection spread by organisms in the hospital environment.
  3. Opportunistic pneumonia affects persons whose immune status is compromised.
  1. Most bacteria are normal inhabitants of the oropharynx and nasopharynx and reach alveoli by aspiration of secretions.  Q
  2. Other routes include inhalation from the environment, hematogenous dissemination.
  3. A number of conditions predispose to infection by depressing the host defenses, including cigarette smoking, chronic bronchitis, alcoholism, severe malnutrition, wasting diseases and poorly controlled diabetes. Q
  4. Bacterial pneumonias should be classified on the basis of the etiologic agent, because clinical and morphologic features, and thus therapies, often vary with the causative organism. Q
Pneumococcal pneumonia
Pneumonia caused by Streptococcus pneumoniae remains a significant problem.
  1. Pneumococcal pneumonia is mostly a consequence of altered defense barriers in the respiratory tract.
  2. The aspiration of pneumococci is also promoted by factors that impair the epiglottic reflex, including exposure to cold, anesthesia, and alcohol intoxication.
  3. Lung injury caused by factors such as congestive heart failure and irritant gases also renders the lung more susceptible to pneumococcal pneumonia. Q
  4. The capsule of the pneumococcus provides a defense against phagocytosis by the alveolar macrophages. Q
  1. In the earliest stage of pneumococcal pneumonia, protein-rich edema fluid containing numerous organisms fills the alveoli.
  2. Marked capillary congestion leads to massive outpouring of polymorphonuclear leukocytes.
  3. The firm consistency of the affected lung is reminiscent of the liver, this stage has been aptly named red hepatizationQ
  4. The next phase, involves lysis of polymorphonuclear leukocytes and appearance of macrophages. 
  5. At this stage, the congestion has diminished, but the lung is still firm (grey hepatization)
A number of complications may follow pneumococcal pneumonia:
  1. Pleuritis.
  2. Pleural effusion.
  3. Pyothorax.
  4. Empyema. Q
  5. Endocarditis or meningitis.
  6. Pulmonary fibrosis is a rare complication
  7. Lung abscess is an unusual complication.

Klebsiella Pneumonia
Commonly associated with alcoholism, diabetes and chronic pulmonary disease are also at risk.

K. pneumoniae has a thick, gelatinous capsule, which is responsible for the characteristic mucoid appearance of the cut surface of the lung.  Q
Staphylococcal Pneumonia

  1. Community-acquired staphylococcal pneumonia is uncommon. Q
  2. Pulmonary infection with Staphylococcus aureus is a common superinfection after influenza and other viral respiratory tract infections. Q
  1. Staphylococcal pneumonia is characterized by abscess development.  Q
  2. Multiple small abscesses.
  3. Cavitation and pleural effusions are common complications.
  4. Staphylococcal pneumonia requires aggressive therapy. Q
Mycoplasma pneumoniae causes atypical pneumonia
  1. The onset of insidious, leukocytosis is absent or slight and the course is prolonged.
  2. The infection characteristically causes a bronchiolitis with a neutrophilic intraluminal exudate and an intense lymphoplasmacytic infiltrate in the bronchiolar wall. Q
  3. Mycoplasma difficult to isolate by traditional culture methods.
  4. The diagnosis is often established on detecting M. pneumoniae antibodies or cold agglutinins. Q
  5. Erythromycin is effective.
Tuberculosis is the classic granulomatous infection. Q
The disease is divided into primary and secondary (or reactivation) tuberculosis.
Primary tuberculosis:
The disease is acquired from the initial exposure to M. tuberculosis, most commonly as a result of inhaling infected aerosols generated when a person with cavitary tuberculosis coughs.
  1. The Ghon complex is the first lesion of primary tuberculosis and consists of a peripheral parenchymal granuloma, often in the upper lobes.
  2. When it is associated with an enlarged mediastinal lymph node a Ranke complex is formed.
  3. Microscopically, a granuloma with central caseous necrosis shows varying degrees of fibrosis.
    1. Apical scarring with the appearance of a fibronodular patch or ill-defined reticular shadow in the upper lung fields on chest x-ray is known as "Simon's focus".
    2. PURL'S LESION - Lesion at the apex of lung in chronic cases.  

Assmann’s Focus - Typically apical (site of highest oxygen tension)

Point to be remember:
TB SIMON'S FOCUS - Early hematogenous seedling in apex of lungs

GHON'S COMPLEX - parenchymal subpleural lesion + draining lymphatics + enlarged caseous   lymph nodes in    primary tuberculosis

RANKE COMPLEX - healed lesions in lung parenchyma and hilar lymph nodes undergoing calcification due to TB

RICH FOCUS - tuberculous caseous foci in brain, meninges and spinal cord
Secondary tuberculosis:
This stage represents either reactivation of primary pulmonary tuberculosis or a new infection in a host previously sensitized by primary tuberculosis. Q

  1. A cellular immune response occurs after a latent interval and leads to formation of many granulomas and extensive tissue necrosis. Q
  2. The apical and posterior segments of the upper lobes are most commonly involved.
  3. A diffuse, fibrotic, poorly defined lesion develops. Some erode into a bronchus creates a tuberculous cavity. Q
  4. Tuberculous cavities range in size from under 1 cm in diameter to large, cystic areas.
  5. The tuberculous cavity often communicates freely with a bronchus, and spreads the infection within the lung. Q
Secondary tuberculosis is associated with a number of complications:
  1. Miliary tuberculosis refers to the presence of multiple, small (size of millet seeds), tuberculous granulomas in many organs.
  2. Hemoptysis.
  3. Bronchopleural fistula occurs when a subpleural cavity ruptures into the pleural space. In turn, tuberculous empyema and pneumothorax result. Q
  4. Tuberculous laryngitis.
  5. Intestinal tuberculosis.
Mycobacterium Avium-Intracellulare (MAI):
  1. In patients who have AIDS, the ability to mount a granulomatous reaction may be impaired, and MAI pneumonia is characterized by an extensive infiltrate of macrophages and innumerable acid-fast organisms.
  1. Actinomycosis is caused by infection with actinomycetes, and the usual pulmonary organism is Actinomyces israelii. They are anaerobic filamentous bacteria.  Q
Pathology Q
  1. Lung lesions consist of multiple, small lung abscesses.
  2. The central necrotic area is purulent and contains colonies of organisms, which form sulfur granules.  Q
  3. The colonies consist of thin, branching, filamentous gram-positive bacteria.
  1. Nocardia is a gram-positive filamentous bacteria that causes an acute progressive or chronic bacterial pneumonia. Q
  2. It is frequently encountered in immunocompromised persons, particularly patients with lymphomas, neutropenia, chronic granulomatous disease of childhood and pulmonary alveolar proteinosis. Q

Fungal Infections

  1. Histoplasmosis:
  1. Histoplasmosis
  2. It is caused by inhalation of Histoplasma capsulatum in infected dust, commonly from bird droppings.
  1. Clinical and pathologic similarities to tuberculosis.
  2. Most infections are asymptomatic and result in lesions comparable to the Ghon complex. Q
  3. The organisms are generally not visible on routine stains and are best seen with a silver stain. Q
  4. Immunocompromised persons are at particular risk for dissemination of Histoplasma within the lungs and spread to other organs.
  1. Coccidioidomycosis:
  1. Lesions are limited to a peripheral parenchymal granuloma, with or without lymph node granulomas. Q
  2. Immunocompromised persons may experience rapid progression of the disease. Q
  1. Cryptococcosis:
  1. Results from inhalation of spores of Cryptococcus neoformans. Q
  2. Lung lesions range from small parenchymal granulomas to several large granulomatous nodules. Q
  3. Occur in immunocompromised persons. Q
  1. Aspergillosis:
  1. Infection of the lungs by Aspergillus species, usually Aspergillus niger or Aspergillus fumigatus. Q
  2. Invasive aspergillosis: occurring almost exclusively as an opportunistic infection in persons.
  3. The lungs exhibit patchy, multifocal areas of consolidation. Invasive aspergillosis is a fulminant pulmonary infection that is not amenable to therapy. Q
  4. Aspergilloma (or mycetoma): Aspergillus species may grow in preexisting cavities.
  5. They proliferate to form a fungus ball within these cavities.
  6. The most important symptom being hemoptysis, owing either to the underlying condition, or less commonly, to fungal infection of the cavity wall.

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