Pathophysiology of pleural effusions

Question 1

Histology of visceral pleura

Answer 1

primarily CT

contributes to elastic recoil

Question 2

Histology of parietal pleura

Answer 2

thin layer of loose CT
BV + lymphatic lacunae
covered by a thin layer of mesothelial cells
produces/absorbs fluid

Question 3

Lymphatic stoma

Answer 3

exists only within the parietal pleura

removes fluid

Question 4

Normal pleural fluid

Answer 4

about 8 ml/ side

pH 7.6

Question 5

Pressure gradient across pleura

Answer 5

oncotic pressures balanced

hydrostatic pressure +6 cm H2O towards visceral pleura

Question 6

Causes of increased pleural fluid entry

Answer 6

increase in permeability (exudate)
increased microvasculature pressure
decreased pleural pressure (atelectasis)
decreased plasma oncotic pressure (low protein)

Question 7

Causes of increased pleural fluid entry from other organs

Answer 7

Hepatic hydrothorax 
Urinothorax 
Chylothorax (from thoracic duct)
CSF
esophagus
pancreas

Question 8

Decreased fluid exit

Answer 8

impaired lymphatic drainage

Question 9

Clinical features of pleural effusion

Answer 9

SOB
Pleuritic chest pain
asymptomatic

Percussion dull, decreased tactile fremitus
auscultation decreased air entry

Question 10

Imaging of pleural effusion

Answer 10

US: close to 100% sensitive
CT with contrast: pleural surface - thickening, tumours etc
not indicated in every case

Question 11

Tx for pleural effusion

Answer 11

Thoracentesis

Question 12

Pleural fluid analysis

Answer 12

Colour (Frank blood - >50% hematocrit, hemothorax)
Smell
Chemistry - protein, LDH, albumin
WBC-D
Cytology - cancer
pH, glucose
gram stains + cultures

> 85% lymphocytes: TB, cancer, rheumatoid
10% eosinophils: pneumo/hemothorax
neutrophils - infections

Question 13

Light’s criteria

Answer 13

Transutae vs exudate pleural fluid (85% sensitive for exudate)
fluid protein/serum protein >0.5
fluid LDH/serum LDH>0.6
fluid LDH > 2/3 upper limit of normal

Question 14

Transudate pleural effusion

Answer 14

low protein and LDH in pleural fluid
intact endothelial membrane
increased hydrostatic pressure or decreased oncotic pressure

Question 15

Exudate

Answer 15

high protein and LDH in pleural fluid

disruption of endothelial membrane

Question 16

DDx of transudate pleural effusion

Answer 16

LUCKI ME
Liver
Urinothorax
CHF
Kidney
Iatrogenic
Myxedema
Embolic

Question 17

DDx of exudate

Answer 17

everything other than transudate
malignancy
infection
PE
serositis due to CT damage

Question 18

Incidence of pleural effusion (causes)

Answer 18

CHF 37.6%
pneumonia 48% non-cardiac effusions
cancer - 24%

Question 19

Parapneumonic effusion

Answer 19

fluid formation - inflammation/infection of fluid
uncomplicated effusion (exudate)
complicated - pH < 7.2
empyema

Question 20

Empyema

Answer 20

Infection of pleural space leading to fibrous peel around the lung
severe sepsis
Chest tube drainage if complicated (low pH)/empyema
if cannot drain properly, may need surgical decortication

Question 21

Malignant effusion

Answer 21

Primary: mesothelioma (cancer of pleura, secondary to asbestosis)
Metastatic - much more common

Question 22

Pathophysiology of malignant effusion

Answer 22

Direct - hematogenous spread, obstruction of lymphatic drainage
Indirect -
  Hypoproteinemia
 Post-obstructive pneumonitis
 Treatment related
 PE
 thoracic duct obstruction
 pericardial involvement