Briefly describe the pleural space.
- Width: 1 mm (under normal circumstances)
- Visceral pleura covers: 1) surface of lungs, 2) interlobar fissure
- Parietal pleura: 1) the surface of chest wall, 2) diaphragm, 3) mediastinum
What are the differences b/t the visceral and parietal pleura?
- Both composed of:
1. Mesothelial layer
2. Basement membrane
3. CT with blood vessels, lymphatics, nerves
- Remember: visceral is LTD (loose cells, tight junction, dense microvilli)
Normal pleural fluid
- Thin layer of fluid: 10-27 micro-m thick (quantity: 1-20 ml)
- Clear, odorless
- Nucleated cells (< 1,500 /m L)
1. 70-80% macrophages, mesothelial cells, monocytes
2. 2% polymorphonuclear leukocytes;
3. 10% lymphocytes
- Protein concentration: 1 - 1.5 g/dL; colloid oncotic pressure (COP) 8 cmH20
- Function: lubrication of the pleural surface (as they glide together as you breathe)
What pressures are important in the formation of a pleural effusion?
- Fluid formation follows the Starling equation
F = K [(Pc - Ppl) - (πc - πpl)
- q depends on a combination of
1. Hydrostatic (P),
2. Colloid osmotic (π),
3. Tissue pressure, and
4. Lymphatic drainage
- Hydrostatic and colloid osmotic pressures most important
- Remember: a pleural effusion is just devo of fluid in the pleural space
How does fluid move in the pleural space?
- Gradient exists between these two pleura
1. Moves from the parietal (systemic circulation; inter-costal arteries) to the visceral (pulmonary circulation)
2. High hydrostatic pressure (100 mL/hr fluid formation) -> low hydrostatic pressure (300 mL/hr fluid absorption)
- Parietal pleura promotes mvmt of fluid into the pleural space via mesothelial junctions
How are proteins and cells removed from the pleural space?
- Proteins, particles, cells are removed by the lymphatics
- Parietal pleura has: stomata -> lymphatic lacunae -> lymphatic ducts -> lymphatics -> mediastinal lymph nodes
- Cells, proteins all have to be removed by the parietal pleura itself
At a basal level, what causes pleural effusion? 2 types?
- Changes in hydrostatic-tissue forces or in oncotic pressure gradient across the pleural space lead to:
1. INC fluid formation (parietal and visceral) and/or
2. DEC fluid resorption (visceral)
- Pleural effusions are divided into:
1. Exudates (rich in protein)
2. Transudates (low in protein)
What are 2 hydrostatic and 2 oncotic changes that can lead to pleural effusion? Exudate types?
Describe an example of pleural effusion due to INC hydrostatic pressure.
- Congestive heart failure (CHF) -> transudative effusion
1. Quantity of effusion proportional to elevation in pulm artery capillary wedge pressure (> 24mmHg)
- Pressure gradient:
1. Oncotic pressure gradient NOT AFFECTED
2. PAP hydrostatic > colloid oncotic
3. Visceral pleura shift from fluid absorption to fluid formation
- Common characteristics: frequently bilateral, cardiomegaly
Describe an example of pleural effusion due to DEC oncotic pressure.
- Malnutrition or renal loss, i.e., nephrotic syndrome
- Decreased production
- Decreased plasma oncotic pressure:
1. Oncotic pressure gradient decreased
2. Hydrostatic pressures NOT AFFECTED
3. Hydrostatic forces from parietal and visceral pleura are unopposed with fluid formation from both sides
- Transudative effusion
Describe an example of pleural effusion due to DEC intrapleural pressure.
- Atelectasis: most common in ICU
- Increased negative pleural pressure:
1. Oncotic pressure gradient not affected
2. Hydrostatic tissue forces pressure gradient > oncotic pressure gr.
3. Increased fluid formation from both sides
- Transudative effusion
Describe an example of pleural effusion due to increased permeability.
- Inflammation, infection, and/or cancer
- Increased vascular permeability:
1. Protein-rich exudate with increased COP in pleural space
2. Oncotic pressure gradient decreased
3. Hydrostatic pressures NOT AFFECTED
4. Increased fluid formation from both sides
What are some of the possible physical exam signs of pleural effusion?
- Physical signs will depend on the size of the effusion
1. Small: may not see anything
2. Moderate: 1) diminished or absent tactile fremitus, 2) diminished or absent breath/voice sounds, 3) dull to percussion
3. Large: 3 signs + contralateral tracheal shift (e.g., away from the effusion)
What are some of the common causes of pleural effusion?
What are the most common malignant causes of pleural effusion?
- Proximity to the pleura -> easier for them to disseminate into the pleural space
What are the radiographic findings for pleural effusion?
- Two major forces control the arrangement of free fluid in the pleural space: (1) gravity and (2) elastic recoil of lung
- Fluid gravitates first at the base of the hemidiaphragm, particularly posteriorly where the sinus is deepest
- As fluid increases it spills into the costophrenic angle (250cc to be visible on PA CXR) and creates a meniscus sign on chest X-ray (see attached image)
- Depends on how much fluid is in there
What happens to pleural effusion fluid in lateral decubitus position?
Free layering by gravity
How should radiographic abnormalities affect the interpretation
- Without other radiographic abnormalities:
1. Tuberculosis, viral pleurisy, pancreatitis
2. Metastatic carcinoma, Meig’s syndrome
3. Lupus, rheumatoid (auto-immune disorders)
4. Pulmonary embolism
5. Nephrotic syndrome, cirrhosis (low albumin)
- With radiographic abnormalities:
1. Parapneumonic effusion -> type of pleural effusion that arises as a result of a pneumonia, lung abscess, or bronchiectasis
2. Carcinoma of the lung, lymphoma, mesothelioma metastatic carcinoma (lymphangitic, hematogenous)
3. Pulmonary embolism with infarction
4. Congestive heart failure
When might you get a bilateral pleural effusion?
- With cardiomegaly:
1. Congestive heart failure (80%): attached image -> chest film from pt being treated for CHF shows a large R pleural effusion and a smaller L side effusion (will improve w/INC diuretics; echo showed EF of 25-30%)
- Without cardiomegaly:
2. Lupus, rheumatoid arthritis (auto-immune disorders)
3. Nephrotic syndrome
4. Esophageal rupture
5. Cirrhosis with ascites (underlying hypoalbuminemia)
What do you see here?
- Pleural effusion on chest CT
- Atelectasis of the lung on the left image