Differentials
Pneumonia
SIGNS / SYMPTOMS
No differentiating signs or symptoms.
INVESTIGATIONS
CXR: consolidation without associated effusion.
Uncomplicated parapneumonic effusion
SIGNS / SYMPTOMS
No differentiating signs or symptoms.
INVESTIGATIONS
Pleural fluid: serous in appearance.
Gram stain and culture: negative.
Pleural fluid pH: >7.2.[1]
Lung abscess
SIGNS / SYMPTOMS
Cough productive of foul-smelling sputum.
INVESTIGATIONS
CXR: cavitating lung lesion with air-fluid level.
Contrast-enhanced thoracic CT: demonstrates thick-walled irregular cavity with indistinct boundary between abscess and normal lung, vessels may be visible passing through the abscess.[33]
Malignant pleural effusion
SIGNS / SYMPTOMS
Longer history of symptoms.
Past medical history of cancer which may be known to be metastatic.
Caution is required as malignancy and infected pleural effusions can coexist.
INVESTIGATIONS
Pleural fluid pH in both malignant and infected effusions: <7.2.
Thoracentesis pleural fluid cytology: may demonstrate malignant cells.
CXR: may demonstrate primary tumor.
Thoracic ultrasound: may demonstrate pleural thickening and nodularity.
CT scan: findings suggestive of malignant pleural effusion are pleural thickening extending onto the mediastinum, circumferential pleural thickening, nodularity, and pleural thickening >1 cm.
Chylothorax
SIGNS / SYMPTOMS
No infective symptoms.
INVESTIGATIONS
Pleural fluid: remains milky in appearance when centrifuged, in empyema debris settles out on centrifuge.
Pleural fluid: triglycerides >110 mg/dL, levels of 50 to 110 mg/dL should be followed by lipoprotein analysis for the detection of chylomicrons.
Esophageal rupture
SIGNS / SYMPTOMS
Recent history of vomiting or retching.
INVESTIGATIONS
Pleural fluid: contains food debris and amylase of salivary origin.
CXR: may show hydropneumothorax.
CT scan: may demonstrate esophageal wall thickening, mediastinal widening, and a pleural space gas-liquid level.
Oral contrast-enhanced CT: may show contrast within the mediastinum.
Esophagram with gastrograffin: reveals the location of rupture. An empyema can often develop secondary to the esophagram.
Hemothorax
SIGNS / SYMPTOMS
History of anticoagulation or bleeding diathesis.
Close temporal relationship with thoracic trauma or iatrogenic intervention in the pleural space.
Caution is required as a hemothorax may become secondarily infected.
INVESTIGATIONS
Pleural fluid: frankly bloody.
Pleural fluid hematocrit: >50% of peripheral blood hematocrit.
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