A small fluid density shadow in the bilateral thoracic cavity usually refers to the presence of a small amount of fluid distribution in the thoracic cavity, which requires prompt medical treatment once detected. Bilateral pleural fluid densities are a kind of descriptive term for imaging examinations. Bilateral pleural fluid densities are usually found during CT examinations, and they are mainly characterized by double dorsal curved low-density shadows with clear boundaries, and are usually accompanied by other lung pathologies. The severity of the disease is usually determined by the amount of pleural effusion, and when the amount of fluid on both sides of the chest cavity is relatively small, the lung tissue can be self-absorbed. When pleural effusion occurs, it is important to consult a doctor and follow the doctor’s instructions for proper treatment.