Pleural Effusion -Etiology, Pathogenesis and Types

Etiology and Pathogenesis

a. Increased hydrostatic pressure in visceral pleura

• Congestive heart failure

b. Decreased oncotic pressure

• Nephrotic syndrome

c. Onstruction of lymphatic drainage from the visceral pleura

• Lung cancer

d. Increased vessel permeability of visceral pleural capillaries

• Pulmonary infarction, pneumonia

e. Metastasis to the pleura

• Metastatic breast cancer

Types of Pleural Effusion

1. Transudates

Transudate is the ultrafiltrate of plasma involving disturbances in Starling pressures. Examples include:

i.    Increased hydrostatic pressure in congestive heart failure

ii.    Decreased oncotic pressure in nephrotic syndrome

2. Exudates

Exudate is the protein rich and cell rich fluid present due to an increased vessel permeablity in acute inflammation. Examples include cases of pneumonia, tuberculosis, infarction, metastasis.

3. Chylous

Chylous indicates interruption of the thoracic duct.

Etiology

i.    Malignancy (most common)

Blocks lymphatic drainage

ii.    Trauma

Iatrogenic tear during surgery or pathologic

iii.    Turbid, milky appearance

• Due to chylomicrons (diet-derived triglyceride
• Chylomicrons form a supranate in a test tube after refrigeration

iv.    PF triglyceride > 110 mg/dL is diagnostic

4. Pseudochylous

i.    Turbid, milky appearance

ii.    Caused by inflammation with increasd amount of necrotic debris

PF cholesterol increased

iii.    Most commonly caused by rheumatoid lung diseaes

Laboratory distinction of transudates versus exudates

i.    Pleural fluid and serum concentration of lactate dehydrogenase (LDH) and protein are most useful.

Ratio of pleural fluid protein and LDH to serum protein and LDH increased sensitivity and specificity

ii.    Additional criteria

1. pH >7.4 indicates a transudate
2. pH <7.4 indicates an exudate

Clinical findings

i.    dullness to percussion

ii.    absent breath sounds

iii.    absent vocal tactile fremitus

iv.    contralaeral shift of the mediastinunm

Only large effusions

Imaging

Blunting of the costophrenic angle

Pleural fluid (PF) transudates versus exudates

Component	Transudate	Exudate
PF protein/serum protein	<0.5	>0.5
PF LDH/serum LDH	<0.6	>0.6
PF LDH	<200 U/L	>200 U/L

LDH, lactate dehydrogenase; PF, pleural fluid