Specific causes of pleural effusion
In addition to classic pulmonary and cardiac pathologies, effusion often develops against the background of systemic disorders:
- Renal diseases: Exudative effusion is possible in uremia, often combined with pericarditis. Nephrotic syndrome causes bilateral fluid accumulation due to hypoproteinemia. Peritoneal dialysis can lead to transdiaphragmatic fluid transfer (more often on the right), which is characterized by a diagnostically high glucose level. A rare condition is urinothorax (urinothorax), occurring in ipsilateral obstructive uropathy.
- HIV/AIDS: In immunocompromised patients, effusion is most commonly caused by pneumonia or non-Hodgkin lymphoma.
- Chylothorax (Chylothorax): Associated with damage or obstruction of the thoracic duct (thoracic duct). The effusion has a milky color due to chylomicrons (triglycerides). Non-traumatic causes are headed by lymphomas, and traumatic causes by iatrogenic surgical injuries.
Pleural empyema: from exudate to pleural peel
Empyema (empyema) is a purulent exudate, most commonly of parapneumonic origin. The natural course of an undrained process goes through three stages:
- Exudative stage: freely flowing fluid with high cellularity (>15,000 leukocytes/mL).
- Fibrinopurulent stage: formation of pronounced adhesions and fibrous strands that are well visualized on ultrasound, impeding drainage.
- Organizational stage: formation of a thick fibrous pleural peel (pleural peel). At this stage, percutaneous drainage is ineffective, and surgical decortication is required.
On CT, empyema is characterized by the split pleura sign (split pleura sign). An important difference from lung abscess: empyema causes lung compression, whereas an abscess causes pulmonary tissue destruction and has a thick, irregular wall.
Diagnostic imaging of pleural thickening
Pleural thickening can be benign (outcome of hemothorax, asbestos exposure) or malignant (mesothelioma, metastases).
| Method | Role and specific signs |
|---|---|
| US | Assessment of the pleural stripe. Helps differentiate loculated effusion from true thickening (using color Doppler). Malignancy is indicated by pleural nodularity. |
| CT | Main modality. Reliable signs of malignancy: circumferential thickening, nodularity, parietal pleural thickness >1 cm, involvement of the mediastinal pleura. |
| MRI | Diffusion-weighted MRI (DW-MRI) reveals the pleural pointillism sign — a marker of malignancy. MRI is also ideal for diagnosing thoracic endometriosis. |
Thoracentesis and drainage rules
Image-guided drainage reduces the rate of complications compared to the "blind" method. The access site is always chosen in the dependent (lowest) part of the accumulation. Needle insertion is performed strictly along the upper margin of the underlying rib to avoid damaging the neurovascular bundle.
Catheter sizes:
- 6–8 F: for simple fluid.
- >8 F (up to 16 F): for viscous, complicated collections under image guidance.
- 36–38 F: surgical drains (e.g., for traumatic hemothorax).
Important limitation: The evacuation procedure is interrupted when a volume of 1.5 liters is reached. Rapid expansion of the collapsed lung can provoke reexpansion pulmonary edema (reexpansion oedema), which develops within several hours.
How to relate the side of traumatic chylothorax and the level of thoracic duct injury: RT – LT. Right-sided = Lower third. Left-sided = Upper two-thirds.
Class and exam questions
How to differentiate empyema from lung abscess on CT?
In empyema, the adjacent lung tissue is compressed (compression), whereas an abscess is characterized by its destruction and the presence of a thick, irregular wall of the lesion itself.
Why is it not allowed to evacuate all fluid at once during pleural puncture?
Removal of more than 1.5 liters of fluid at a time can lead to rapid expansion of a long-collapsed lung and the development of a formidable complication — reexpansion pulmonary edema.
Which effusion parameter requires mandatory chest tube placement?
A strict predictor of the need for drainage is a decrease in pleural fluid pH below 7.2.
What does right-sided effusion indicate in a patient on peritoneal dialysis?
This indicates direct transdiaphragmatic fluid transfer from the abdominal cavity. Such effusion is distinguished by a diagnostically high glucose level.
What else to study on this topic
- Thoracic endometriosis: MRI findings and magnetic susceptibility artifacts
- Split pleura sign on CT in empyema
- Evaluation of anterior mediastinal masses in children (lymphomas, leukemias, teratomas)
- Congenital venolobar syndrome (scimitar syndrome) and IVC drainage anomalies
- CT signs of malignant mesothelioma and staging
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