Stephen, there are quite a few possible causes of a pleural effusion (a collection of fluid in the chest cavity). Neoplasia (a tumor, e.g.) is just one possible cause. It can also arise secondary to heart disease, a lack of albumin in the body, lung lobe torsion, infection, a ruptured lymphatic duct, and bleeding into the chest cavity. The fluid that was removed must be analyzed by our pathologist; in particular, for its cellularity. Cells seen may have come from a tumor that wasn't readily visible in X-rays and so the diagnosis of a tumor can be made in that manner. If so, the type of tumor will dictate whether or not the tumor can be removed.
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