A tuberculous pleural effusion is one of the manifestations of pleural tuberculosis. It can have variable presentation ranging from a largely benign pleural effusion, with potential to completely resolve to a complicated effusion with loculations, pleural thickening and potentially progressing to a tuberculous pleural empyema.
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Pathology
It tends to be a lymphocytic effusion. Build up of fluid in the pleural space occurs as a result of a combination of factors with the inciting factor often being a rupture of a subpleural caseous focus, leading to entry of antigen into the pleural space and with initial inflammatory reaction to the antigen causing an increase in capillary permeability with subsequent influx of proteins which in turn stimulate a higher rate of pleural fluid formation.
Diagnosis
An initial diagnostic aspirate with pleural fluid analysis including biomarkers such as the following may be helpful in the correct clinical context.
- adenosine deaminase: usually above 40 U/L 3
- gamma interferon IFN-ɣ
A definitive diagnosis may require demonstration of evidence of caseating granulomata or microbiological evidence of Mycobacterium tuberculosis on smear or culture.
Radiographic features
CT
Pleural phase CT is probably best at diagnosis in suspected cases. It often shows a pleural effusion and can be accompanied by diffuse thickening of both the visceral and parietal pleura (may give a split pleura sign in this instance 2).
Differential diagnosis
In certain situations consider:
- other forms of pleural empyema
- pleural lymphoma
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