Definition - excess amount of fluid in the pleural space (normally up to 25 mL)
Etiology
disruption of normal equilibrium between pleural fluid formation/entry and pleural fluid absorption/exit
pleural effusions are classified as transudative or exudative
distinguish clinically using Light's Criteria (Table), which has a sensitivity of 98% and
specificity of 83% for identifying exudative pleural effusions
Transudative effusions are usually bilateral, not unilateral.
Exudative effusions can be bilateral or unilateral.
Laboratory Values in Transudative and Exudative Pleural Effusion ("Light's Criteria and Modified Light's Criteria")
All criteria for transudate must be fulfilled to be considered a transudative effusion. If any one of the criteria for exudates is met – it is an exudate.
Transudative Pleural Effusions
• pathophysiology: alteration of systemic factors that affect the formation and absorption of pleural fluid (e.g. increased capillary hydrostatic pressure, decreased plasma oncotic pressure)
• etiology
CHF: usually right-sided or bilateral cirrhosis
nephrotic syndrome, protein losing enteropathy, cirrhosis
pulmonary embolism (may cause transudative but more often causes exudative effusion)
peritoneal dialysis, hypothyroidism, CF, urinothorax
Exudative Pleural Effusions
• pathophysiology: ↑ permeability of pleural capillaries or lymphatic dysfunction
• etiology (see Table)
Exudative Pleural Effusion Etiologies
Signs and Symptoms
• often asymptomatic
• dyspnea: varies with size of effusion and underlying lung function
• pleuritic chest pain
• inspection: trachea deviates away from effusion, ipsilateral decreased expansion
• percussion: decreased tactile fremitus, dullness
• auscultation: decreased breath sounds, bronchial breathing and egophony at upper level, pleural friction rub
Investigations
CXR
must have >200 mL of pleural fluid for visualization on PA film
lateral: >50 mL leads to blunting of posterior costophrenic angle
PA: blunting of lateral costophrenic angle
dense opacification of lung fluids with concave meniscus
decubitus: fluid will shift unless it is loculated
supine: fluid will appear as general haziness
thoracentesis: indicated if pleural effusion is a new finding; be sure to send off blood work (LDH, glucose, protein) at the same time for comparison)
risk of re-expansion pulmonary edema if >1.5 L of fuid is removed
inspect for colour, character, and odour of fluid
analyze fluid (see Tables)
pleural biopsy: indicated if suspect TB, mesothelioma, or other malignancy (and if cytology negative)
± U/S: detects small effusions and can guide thoracentesis
treatment depends on cause, ± drainage if symptomatic
CT can be helpful in differentiating parenchymal from pleural abnormalities
CT Features of Malignant Effusion
• Multiple pleural nodules
• Nodular pleural thickening
CT Features of Exudative Effusion
• Loculation
• Pleural thickening
• Pleural nodules
• Extrapleural fat of increased density
Appearance of Pleural Fluid
• Bloody: trauma, malignancy
• White: chylothorax, empyema
• Black: aspergillosis, amoebic liver abscess
• Yellow-green: rheumatoid pleurisy
• Viscous: malignant mesothelioma
• Ammonia odour: urinothorax
• Food particles: esophageal rupture
Treatment
• thoracentesis
• treat underlying cause
• consider indwelling pleural catheter or pleurodesis in refractory effusions
Analysis of Pleural Effusion