SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 011

1. What is the difference between bronchopneumonia and lobar pneumonia?

Bronchopneumonia is a patchy, multifocal bacterial infection centered on bronchioles and adjacent alveoli. It commonly affects infants, elderly individuals, and debilitated patients. Multiple foci of consolidation are scattered throughout one or more lobes, often involving both lungs.

Lobar pneumonia, in contrast, involves uniform consolidation of an entire lobe or a large portion of it. It is classically caused by Streptococcus pneumoniae. Bronchopneumonia is usually caused by organisms such as Staphylococcus aureus, Haemophilus influenzae, or gram-negative bacteria.

Lobar pneumonia progresses through well-defined pathological stages. Bronchopneumonia has a more irregular distribution and variable progression.

Both conditions impair gas exchange and may lead to respiratory failure if severe.

2. List the defense mechanisms that protect against bacterial pneumonia.

The respiratory tract possesses several defense mechanisms that prevent bacterial infection. The nasal passages filter inhaled particles. The mucociliary escalator removes microorganisms trapped in mucus. Cough and sneeze reflexes expel foreign material from the airways. Alveolar macrophages phagocytose inhaled bacteria reaching the alveoli.

Secretory IgA antibodies protect the respiratory mucosa. Complement proteins and neutrophils participate in bacterial killing. Surfactant proteins also contribute to innate immune defense. Normal respiratory flora inhibit colonization by pathogenic organisms.

Intact immunity and effective airway clearance are essential for preventing bacterial pneumonia.

3. Name the four classical stages of lobar pneumonia.

Lobar pneumonia classically progresses through four pathological stages. The first stage is congestion, occurring during the initial 24 hours, characterized by vascular engorgement and edema. The second stage is red hepatization, in which alveoli become filled with red blood cells, neutrophils, and fibrin, giving the lung a liver-like consistency.

The third stage is gray hepatization, during which red blood cells disintegrate while fibrin and leukocytes remain abundant. The fourth stage is resolution, where enzymatic digestion removes the exudate and normal lung architecture is restored.

Macrophages play a major role during resolution. Complete recovery usually occurs if treatment is prompt. Delayed resolution may lead to complications such as abscess formation or fibrosis.

4. Name the main pathologic characteristics of primary atypical pneumonia.

Primary atypical pneumonia is usually caused by viruses, Mycoplasma pneumoniae, Chlamydia, or other atypical organisms. The infection primarily affects the alveolar septa rather than filling alveolar spaces with exudate.

Grossly, the lungs show patchy areas of congestion without extensive consolidation. Microscopically, the interstitium contains mononuclear inflammatory cells, mainly lymphocytes and macrophages. The alveolar walls become thickened because of inflammatory infiltration.

Alveolar spaces contain little or no purulent exudate. Hyaline membranes may develop in severe viral infections.

Symptoms are often milder than in typical bacterial pneumonia despite widespread radiological changes. Most patients recover completely with appropriate treatment.

5. What are the most frequent conditions that predispose to the formation of pulmonary abscess?

Pulmonary abscess is a localized area of suppurative necrosis within the lung producing a cavity filled with pus. Aspiration of oropharyngeal secretions is the commonest predisposing factor, particularly in unconscious or alcoholic patients.

Necrotizing bacterial pneumonia may also lead to abscess formation. Bronchial obstruction caused by tumors or foreign bodies predisposes to secondary infection. Septic emboli from infective endocarditis can produce multiple lung abscesses. Tuberculosis and fungal infections occasionally result in cavitary lesions. Immunocompromised patients are at increased risk. Poor oral hygiene increases aspiration of anaerobic bacteria.

Untreated abscesses may rupture into the pleural cavity or bloodstream, causing serious complications.

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DR.C.GANESAN M.D

PROFESSOR OF MEDICINE