Pleural fluid cytology was taken as confirmation of malignancy only in the presence of a confident histopathology opinion reporting confirmed malignant cells on cytology ± immunostaining as required. In these cases, no further investigation to establish diagnosis was required. Negative pleural fluid cytology was not taken as definitive proof of benign aetiology (hence clinical follow-up as below was pursued).

*All patients with a diagnosis of benign disease were followed up for a period of 12 months (at our institution or the referring institution), in which time there was no evidence of malignancy developing within the pleura or elsewhere as the cause of the presenting pleural effusion.

†Two patients underwent non-diagnostic percutaneous pleural biopsy and subsequent diagnostic thoracoscopy. These patients are only listed once as thoracoscopic biopsies.