胸膜炎（Pleurisy）是一种胸膜腔疾病。可分为感染性、肿瘤性和变态反应性胸腔积液。感染性的胸膜炎一般由结核、化脓性细菌、真菌、寄生虫引起。渗液机理可分为漏出性、渗出性。按积液性质可分为出血性、乳糜性、胆固醇性、脓性。正常人的胸膜腔有少量液体，是由毛细血管的动脉端滤过形成，起润滑作用，通过再吸收回到血液系统。病理情况下滤过与再吸收过程的平衡被打破，就产生积液。胸膜炎的诊断可通过X射线、肉眼、细胞学、生物化学、病因学的方法。

Pleurisy (also known as pleuritis) is an inflammation of the pleurae, the membranes of the pleural cavity surrounding the lungs. There are many possible causes of pleurisy but viral infections spreading from the lungs to the pleural cavity are the most common. The inflamed pleural layers rub against each other every time the lungs expand to breathe in air. This can cause sharp pain when breathing, also called pleuritic chest pain. The condition may either be primary or secondary and is often associated with a pleural effusion.