Medical Content Created by the Faculty of the
Harvard Medical School
Some infections and diseases cause fluid to accumulate in the space between the lung and the rib cage or between the lung and the diaphragm. This collection of fluid is called a pleural effusion. A pleural effusion might be detected on a chest x-ray. Sampling this fluid is important because it enables doctors to understand what caused the fluid to collect and how to treat the problem. The fluid can be sampled with a needle.