Malignant Pleural Effusion and Pleurodesis
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Direct answer
Malignant pleural effusion is pleural fluid caused by tumour involvement of the pleura, most often from lung, breast, ovarian cancer or lymphoma. A single cytology sample can miss malignant cells, so repeat sampling or pleural biopsy is often needed before the diagnosis is confirmed. Symptomatic recurrence is controlled by pleurodesis, usually with talc, or by an indwelling pleural catheter.
What you must remember
- Common primaries: lung cancer is the commonest source overall, while breast and ovarian cancers dominate in women, with lymphoma and mesothelioma also important.
- Exudate pattern: malignant effusions are typically exudative, identified by Light's criteria of pleural protein or LDH ratios.
- Cytology yield: a single thoracentesis gives an incomplete yield, so repeat cytology or closed pleural biopsy is used when suspicion stays high.
- Trapped lung: a non-expandable lung prevents the pleural layers from apposing, and this predicts pleurodesis failure.
- Talc pleurodesis: sterile talc given through a chest drain or by thoracoscopic poudrage is effective in many patients, and pain is a common side effect.
- Indwelling catheter: a tunnelled pleural catheter allows outpatient drainage and suits trapped lung or limited life expectancy.
- Prognosis: a malignant effusion signals advanced disease, so palliative choices should favour quick, minimally invasive relief.
A pathway from effusion to durable control
A 64-year-old woman with breast cancer has breathlessness and a large right effusion that has returned twice after drainage. The aim is to confirm the cause and then choose a method that stops the fluid from coming back.
- Confirm the cause: send fluid for cytology at thoracentesis, and if the result is negative with strong suspicion, proceed to closed pleural biopsy or thoracoscopy.
- Check for trapped lung: a chest radiograph or ultrasound after drainage shows whether the lung re-expands, since a non-expandable lung predicts pleurodesis failure.
- Drain in measured volumes: therapeutic drainage relieves dyspnoea, but rapid large-volume removal risks re-expansion pulmonary oedema, so volumes are limited.
- Choose pleurodesis or a catheter: talc slurry or poudrage suits an expandable lung with reasonable performance status, whereas an indwelling pleural catheter suits trapped lung or failed pleurodesis.
- Treat the primary: systemic therapy for the underlying cancer continues, because controlling the effusion alone does not improve survival.
Where the exam tries to catch you
Most errors come from treating the fluid rather than the cause, or from using the wrong device for a trapped lung.
- Trap: repeating a single negative cytology and calling the effusion benign Correct: one negative sample does not exclude malignancy, so repeat sampling or pleural biopsy is needed.
- Trap: using a chest drain alone for recurrent symptomatic effusion Correct: a drain only empties the pleura, and durable control needs pleurodesis or an indwelling catheter.
- Trap: expecting talc to work in a trapped lung Correct: the lung cannot appose the pleura, so an indwelling pleural catheter is preferred.
- Trap: draining large volumes rapidly Correct: rapid removal can cause re-expansion pulmonary oedema, so drainage proceeds in measured volumes.
Frequently asked questions
Which primaries most commonly cause malignant pleural effusion?
Lung cancer is the commonest cause of malignant pleural effusion overall. Breast and ovarian cancers are the leading primaries in women, while lymphoma and mesothelioma also cause malignant effusions.
Why does a negative pleural cytology not exclude malignancy?
A single cytology sample can miss scanty malignant cells, so the yield at one thoracentesis is incomplete. Repeat cytology or closed pleural biopsy is therefore used when the clinical suspicion of malignancy remains high.
When is an indwelling pleural catheter preferred over pleurodesis?
An indwelling pleural catheter is preferred when the lung is trapped, when pleurodesis has failed, or when life expectancy is short. It allows the patient to drain fluid at home without a prolonged hospital stay.
What is trapped lung and why does it matter for pleurodesis?
Trapped lung is a non-expandable lung held down by fibrous visceral pleura or tumour encasement. Because the pleural surfaces cannot appose, pleurodesis is unlikely to succeed and an indwelling pleural catheter is the usual alternative.
Which criteria classify a pleural effusion as an exudate?
Light's criteria classify an effusion as an exudate if the pleural to serum protein ratio exceeds 0.5, the pleural to serum LDH ratio exceeds 0.6, or the pleural LDH exceeds two-thirds of the upper limit of normal serum LDH. Malignant effusions usually meet these criteria.