How can tuberculosis cause fluid to collect around a lung?

Tuberculosis can cause fluid to collect around a lung—a condition known as pleural effusion—when the infection breaks through the lung tissue and enters the pleural space. The pleural space is the area located between the membrane covering the lung and the membrane lining the thoracic cage.12

When a tuberculous infection reaches this space, it triggers an inflammatory response. This inflammation can lead to the accumulation of watery fluid between the two pleural layers. In some cases, this process may be accompanied by pleurisy, which is an inflammation of the pleura that often causes chest pain. If left untreated, the accumulation of fluid can become significant, potentially leading to disabling shortness of breath.321