Pulmonary edema, pneumonias

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Pulmonary Edema and Pneumonias

I. Pulmonary Edema

1. Definition

Pulmonary edema is a condition characterized by abnormal accumulation of fluid in the lung interstitium and alveolar spaces, leading to impaired gas exchange and respiratory insufficiency.

2. Pathogenesis

Fluid accumulation occurs when the balance between:

  • Hydrostatic pressure
  • Oncotic pressure
  • Capillary permeability
  • Lymphatic drainage

3. Classification

A. Cardiogenic Pulmonary Edema

Caused by increased hydrostatic pressure due to heart disease.

Common causes:

  • Left-sided heart failure
  • Mitral valve disease
  • Acute myocardial infarction
  • Hypertensive crisis
  • Cardiomyopathies

B. Non-cardiogenic Pulmonary Edema

Caused by increased capillary permeability.

Common causes:

  • Acute respiratory distress syndrome (ARDS)
  • Sepsis
  • Severe trauma
  • Inhalation of toxic gases
  • Near drowning
  • Acute pancreatitis

4. Morphology

Gross Features:

  • Heavy, wet lungs
  • Frothy, blood-tinged fluid on section

Microscopic Features:

  • Alveoli filled with pale eosinophilic fluid
  • Capillary congestion
  • In chronic cases: hemosiderin-laden macrophages (“heart failure cells”)

5. Clinical Features

  • Dyspnea, orthopnea
  • Cough with pink frothy sputum
  • Cyanosis
  • Crackles on auscultation

6. Complications

  • Hypoxemia
  • Secondary infections
  • Pulmonary fibrosis (chronic cases)
  • Respiratory failure

II. Pneumonias

1. Definition

Pneumonia is an inflammatory disease of the lung parenchyma, primarily involving the alveoli, usually caused by infectious agents.

2. Etiological Classification

A. Bacterial Pneumonia

  • Streptococcus pneumoniae (most common)
  • Staphylococcus aureus
  • Klebsiella pneumoniae
  • Haemophilus influenzae

B. Viral Pneumonia

  • Influenza virus
  • RSV
  • SARS-CoV-2
  • Adenovirus

C. Atypical Pneumonia

  • Mycoplasma pneumoniae
  • Chlamydia pneumoniae
  • Legionella pneumophila

D. Fungal Pneumonia

  • Candida
  • Aspergillus
  • Histoplasma

3. Anatomical (Morphological) Classification

A. Lobar Pneumonia

Involves entire lobe of lung.

Stages:

  1. Congestion
  2. Red hepatization
  3. Gray hepatization
  4. Resolution

Common organism: Streptococcus pneumoniae

B. Bronchopneumonia

  • Patchy consolidation around bronchioles
  • Often bilateral
  • Common in children and elderly

C. Interstitial (Atypical) Pneumonia

  • Involves alveolar septa
  • Minimal alveolar exudate
  • Usually viral or Mycoplasma

4. Pathogenesis

  1. Entry of organism into alveoli
  2. Activation of alveolar macrophages
  3. Recruitment of neutrophils
  4. Formation of inflammatory exudate
  5. Impaired gas exchange

5. Morphology

Gross:

  • Consolidated areas
  • Firm, airless lung tissue

Microscopy:

  • Alveoli filled with neutrophils, fibrin, bacteria
  • Septal thickening (interstitial pneumonia)

6. Clinical Features

  • Fever, chills
  • Productive cough
  • Chest pain
  • Dyspnea
  • Leukocytosis

7. Complications

  • Lung abscess
  • Empyema
  • Bacteremia and sepsis
  • Organization → pulmonary fibrosis
  • Respiratory failure


CITATION:

  • Robbins & Cotran Pathologic Basis of Disease, 10th Edition
    • Kumar, V., Abbas, A. K., Aster, J. C.
    • Robbins & Cotran Pathologic Basis of Disease, 10th Edition
  • Fishman’s Pulmonary Diseases and Disorders
    • Fishman, A. P. et al.
    • Fishman’s Pulmonary Diseases and Disorders, 5th Edition
    • McGraw-Hill