Tuberculous pleurisy can also cause pericardial effusion. Firstly, tuberculous pleurisy is actually caused by the tubercle bacillus, a type of immune response in the human body that manifests as inflammation in the serous cavity. The serous cavities include various types such as the pleura surrounding the lungs, the pericardium around the heart, and the peritoneum in the abdomen. Therefore, tuberculous inflammation can occur in multiple serous cavities, including the pleura, pericardium, and abdominal cavity. Of course, when diagnosing, one cannot solely rely on the presence of effusion in multiple serous cavities to diagnose tuberculous pleurisy. Instead, it is essential to aspirate the pleural fluid and test certain markers in it, such as adenosine deaminase and lactate dehydrogenase. Most importantly, the presence of acid-fast bacilli in the fluid should be checked. If detected, it can generally be diagnosed as tuberculous.