Unilateral Pleural Effusion

Toms Franquet, MD, PhD

DIFFERENTIAL DIAGNOSIS

Common

Parapneumonic Effusion
Neoplastic Diseases
- Mesothelioma
- Primary Lung Cancer
- Breast Cancer
- Pleural Metastases
- Lymphoma
Hepatic Cirrhosis
Pancreatitis
Trauma

Less Common

Pulmonary Embolism
Myxedema
Rheumatoid Pleuritis
Chylothorax
Renal Disease
HIV Infection

Rare but Important

Catamenial Hemothorax
Yellow Nail Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Pleural effusions result from pleural, parenchymal, or extrapulmonary disease
- Transudative effusions: Imbalance of hydrostatic and oncotic forces
- Exudative effusions: From pleural diseases or decreased lymphatic drainage
CT generally more sensitive than radiography for detection of relatively small volumes of pleural fluid
Pleural pseudotumor: Accumulation of pleural fluid within interlobar fissure; vanishing tumors: Disappearance of effusions after treatment
- Fluid in fissure has curvilinear edge concave to hilum
- Minor fissure pseudotumor may be mistaken for pulmonary mass
Large and massive pleural effusions are more likely to be malignant
- Half of malignant effusions do not reveal any pleural finding apart from effusion
- Pleural nodules and circumferential pleural thickening are highly specific for malignancy
Ultrasonography: Useful to demonstrate pleural loculations
- Fibrinous septations are better visualized on ultrasound than on CT scans

Helpful Clues for Common Diagnoses

Parapneumonic Effusion
- Bacteria
  - In CAP, most commonly associated organisms are gram-positive aerobic bacteria
  - In nosocomial infections, gram-negative aerobes (H. influenzae, E. coli, P. aeruginosa, and Klebsiella)
  - CECT: Pleural thickening and loculated fluid; split pleura sign of empyema: Fluid between enhancing thickened pleural layers
- Tuberculosis
  - Thick pleural rind: Usually unilateral
- Fungi
  - Rare causes of pleural effusion
Neoplastic Diseases
- Mesothelioma
  - Pleural thickening (89%)
  - Unilateral pleural effusion (87%)
  - Mediastinal pleural thickening (85%)
- Primary Lung Cancer
  - Almost always ipsilateral pleural effusions
  - Infrequently bilateral
- Breast Cancer
  - Ipsilateral pleural effusion in 83% of cases
- Pleural Metastases
  - Adenocarcinoma most common tumor to metastasize to pleura
  - Thymomas may result in pleural dissemination: “Drop metastases”
  - CT: Irregular pleural thickening and small nodules at interlobar fissures
  - CECT: Variable enhancement
- Lymphoma
  - Prevalence of pleural disease in both Hodgkin and non-Hodgkin lymphoma is similar (26-31%)
  - Usually occurs as part of disseminated disease
  - Contrast enhancement of parietal pleura
  - Coexistent involvement of parietal pleura, paraspinal region, and extrapleural space
Hepatic Cirrhosis
- Associated with transdiaphragmatic movement of ascites
- Right-sided, unilateral 70%; left sided 15%; bilateral 15%
- Small to massive
Pancreatitis
- Usually left-sided (70%) or bilateral (15%)
- > pleural fluid amylase level is not specific indicator of pancreatitis
- Pleural amylase values may be elevated in
  - Acute pancreatitis, pancreatic pseudocyst, rupture of esophagus, and ruptured ectopic pregnancy
  - Approximately 10% of malignant effusions have raised pleural amylase levels (especially adenocarcinoma)
Trauma
- CT of acute hemothorax: Fluid-fluid level or increased density of pleural fluid

Helpful Clues for Less Common Diagnoses

Pulmonary Embolism
- Pleural effusions in 30-50% of patients
  - Unilateral and small (85%)
  - Pleuritic pain: 75% of patients with pleural effusion
- No specific pleural fluid characteristics
  - Pleural fluid red blood cell count > 100,000/mm³ suggests malignancy, pulmonary infarction, or trauma
Myxedema
- Massive cardiomegaly (pericardial effusion) and thoracic inlet mass (goiter)
- Unilateral or bilateral pleural effusions; small to moderate in size
Rheumatoid Pleuritis
- Middle-aged men with positive rheumatoid factor
Chylothorax
- Presence of chyle in pleural space: Malignancy (lymphoma and metastases), trauma, post-surgery, tuberculosis, LAM, sarcoidosis, and amyloidosis
Renal Disease
- Peritoneal or hemodialysis
  - Like ascites-related pleural effusions, usually on right
HIV Infection
- Causes of effusions: Kaposi sarcoma (30%), parapneumonic effusion (28%), tuberculosis (14%), Pneumocystis jiroveci pneumonia, and lymphoma

Helpful Clues for Rare Diagnoses

Catamenial Hemothorax
- Occurs in 14% of patients with pleural endometriosis
  - 85-90% occur on right (only 5% occur bilaterally)
Yellow Nail Syndrome
- Rhinosinusitis, pleural effusions, bronchiectasis, lymphedema, and yellow nails