How Likely Is It CAT Scan To Pick Up A

How likely is it CAT scan to pick up a lung cancer if there is pleural effusion present? In other words, does the pleural effusion prevent the visualization of the potential tumor? How about in the case of a partially collapsed lung? Husband has a pleural effusion which is coming up inconclusive on cytology but he has had four separate CAT scans in a short time and none of which are showing any suspicious mass.