A 75 year old man with no past medical history presents with increasing shortness of breath over 6 months. He previously worked at a shipyard where he had significant exposure to asbestos. He has a large right-sided pleural effusion. Pleural aspiration is performed and reveals an exudate but cytopathological examination identifies no malignant cells. CT scanning reveals circumferential pleural thickening but no other abnormalities. Which test is most likely to give a diagnosis?

Direct visualisation and targeted biopsy of any pleural lesion provides the best chance of a tissue diagnosis. Mesothelioma cannot b~ diagnosed on cytopathological examinatipn of pleural fluid. Bronchoscopy would not help with pleural disease but may be helpful if there were an endobronchial lesion with pleural metastases. Echocardiogram is not c6nsidered helpful because there is pleural thickening as well as a right-sided pleural effusion, so heart failure is an unlikely cause.