Fluid in the chest on X-ray can mean that there is fluid in the lung (edema), or around it (pleural effusion). There can also be fluid in other parts of the chest like in the mediastinum, along the chest wall or under the skin. Fluid in the chest does not tell us exactly where the fluid is. It also does not indicate the reason for it. Fluid in the chest can cause problems with breathing and distress.
On chest X-ray, fluid in the lungs or pulmonary edema can be caused by heart and non heart related causes. In practice, the most common reason I see edema related to heart troubles is with left heart failure. Other heart related causes include arrhythmias, inflammation of heart muscle, and problems of the mitral valve. Non heart related causes of fluid in the lungs are many. Everything from fluid overload, drowning, transfusions, high altitude, drugs including many others.
On chest X-ray, fluid in the lungs can be subtle and seen as scattered extra white lines in the lungs or confluent white densities spreading peripherally depending on the severity. The cause of the edema is not generally known from the X-ray . The clinical history is more helpful. The appearance of fluid in the lungs on X-ray can also be seen with other conditions like infection.
Fluid around the lungs accumulates in the pleural space. There are numerous causes of the fluid accumulation. The fluid can form from heart failure, liver disease, cancer, clots to the lung, pneumonia, tuberculosis, trauma in addition to many others. It is often not possible to tell the cause from an X-ray alone. It is also not possible to tell what the consistency of the fluid is. Like if it’s blood, pus or simple fluid. The history of the patient is helpful.
Fluid in the pleural space has a characteristic appearance on chest X-ray with small amounts of fluid first blunting the space between the lung and periphery of the diaphragm. As more accumulates, it rises upward and appears to opacity the lung. Large collections can cause a white out appearance of the chest.
Fluid can also accumulate in the center of the chest or mediastinum. This can occur after surgery, from infections or trauma. This is often not detected on chest X-ray but on CT. Fluid can accumulate along the chest wall from trauma, infections, or following surgery. This is also not well seen on X-ray and CT is needed to make the diagnosis. Fluid can also accumulate under the skin for various reasons.
Fluid in the chest on X-ray does not tell us where the fluid is exactly or what the cause is. Fluid can accumulate anywhere in the chest but is most common in the lungs and around it. Other collections of fluid are best diagnosed with CT. Fluid is treated based on where it is and what the cause is. Sometimes treating the underlying condition will cause the fluid to resolve and other times it needs to be taken out, like when it accumulates around the lung in some cases.