Serous Membrane
Visceral and parietal division, approximately equal surface area. Each is 1 layer of mesothelial cells, basement membrane, connective tissue, microvessels and lymphatics

Mesothelial Cells
Single layer, pleomorphic. Surface microvilli, more dense on visceral side of pleura

Opening between cells, 2-12 um, only on the parietal surface. The usual exits into lymphatic lacunae for liquid, protein, and cells

Blood Supply
Some controversy. Human visceral pleura supplied by systemic bronchial vessels, drain through fairly large capillaries to pulmonary veins. Parietal blood from adjacent chest wall, drainage to bronchial veins; diaphragmatic pleura supply from nearby arteries, drainage to inferior vena cava and brachiocephalic trunk

More dense lower and toward the mediastinum. Drainage toward hilum either via lung or pleura itself. Stomata lead to lacunae which form valves. Drain to mediastinum via intercostal route depending on origin. Visceral pleural drainage to middle mediastinal nodes or posterior (lower lobes)

Physiologic Principles

Misconceptions or Recent Advances

True Concepts


Fluid accumulates in pleural space.

Irrespective of the nature of fluid, radiologically they will look similar. You are looking at pleural effusion on left.

Radiological criteria are:

Compare the Costophrenic angle before and after clearance of effusion.

Note also lack of identifiable left diaphragm before and visible diaphragm after clearance of fluid (Silouhette sign principle).

Pleural Effusion

Physical Findings

  1. Mediastinum is in midline to start with and gradually gets shifted to opposite site as the pleural pressure becomes positive.
  2. Chest Expansion decreases on the side of effusion due to decreased ventilation.
  3. Resonance is dull and flat to percussion. Dullness is most in posterior base in erect position. Flatness is recognized by tapping the chest with flat of your hand. Traubes space will be obliterated on left sided effusions.
  4. Breath Sounds are decreased since the ventilation to that hemithorax is decreased. Fluid is a good conductor of sound. If there is underlying consolidation a good bronchial breathing will be heard over the effusion. In massive effusions with completely atelectic lung and patent airways one can also hear bronchial breathing over the effusion.
  5. Voice Transmission decreases and follows breath sound characteristics. Egophony is noted along the upper margin of the fluid. This is probably due to a thin film of fluid separating pleural space.
  6. Adventitious Sounds: None
  7. Hemithorax size is larger due to loss of negative pressure in pleural space.
  8. Effort of Ventilation: Respiratory rate increases and use of accessory muscles can be recognized.
  9. Effect on Function: Can lead to central cyanosis.


Pleural Fluid Analysis (Diagnostic Tests)


Percutaneous Pleural Biopsy


Open Biopsy


Specific Diagnoses


Selected Exudates (There are many other causes besides these )


  1. Light RW: Pleural Disease, 2nd edition. Philadelphia, Lea and Febiger, 1990.
  2. Light, RW et al: Parapneumonic effusions. Am J Med 69:985- 986, 1980.
  3. Sahn SA: State of the art: The pleura. Am Rev Respir Dis 138:184-234, 1988.
  4. Sahn, SA, Good, JT Jr: Pleural fluid pH in malignant effusions. Ann Intern Med 108:345-349, 1988.