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 co-exist.
INVESTIGATIONS
Pleural fluid pH in both malignant and infected effusions: <7.2.
Thoracentesis pleural fluid cytology: may demonstrate malignant cells.
CXR: may demonstrate primary tumour.
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.
Oesophageal 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 oesophageal wall thickening, mediastinal widening, and a pleural space gas-liquid level.
Oral contrast-enhanced CT: may show contrast within the mediastinum.
Oesophagram with gastrograffin: reveals the location of rupture. An empyema can often develop secondary to the oesophagram.
Haemothorax
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 haemothorax may become secondarily infected.
INVESTIGATIONS
Pleural fluid: frankly bloody.
Pleural fluid haematocrit: >50% of peripheral blood haematocrit.
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