The diaphragm separates the chest and abdominal cavities and is the main muscle of respiration. A common finding on chest X-ray is elevation of the diaphragm which means that the muscle is higher then is usually found. The diaphragm is usually smooth and dome shaped found on both sides of the chest at roughly the same position or slightly different. The causes are varied and the chest X-ray is a often where this diagnosis is found. This can be an incidental finding or related to the cause of your breathing symptoms.
The diaphragm can be elevated when the lung above it is smaller then it should be. Perhaps a piece of the lung has been removed for some reason like cancer. There could be a piece of the lung that is collapsed, called atelecatasis. These causes will be seen on the chest X-ray and can be suggested in the diagnosis.
The diaphragm itself can also be the cause of the elevation. The diaghragm is controlled by the phrenic nerve which travels from the neck, through the chest next to the heart and then to the diaphragm. You can imagine lesions or abnormalities could damage or pinch the nerve. Cancers, traumas, pneumonia or other inflammatory process involving the nerve, or direct compression by an aneurysm or other process.
Another cause is called diaphgramic eventration in which a part of the diaphgram is elevated causing a bulge instead of a smooth contour. This is caused by parts of the dipahgram not having muscle fibers, resulting in stretching. This appearance can have other possibilities such as a mass, hernia or pneumonia.
Abnormalities pushing up against the diaphragm from below can also cause it to look elevated on a chest X-ray. The liver is positioned just below the diaphragm, so a mass of the liver or around it can cause the diaphragm to be elevated. On the left side, a big stomach filled with food or gas can cause the diaphragm to appear elevated. Sometimes distended colon can also come underneath the diaphragm and cause it to look elevated.
Other diagnosis can mimic an elevated diaphragm. This can be a tumor of the diaphragm or pleura covering the diaphragm. A subpulmonic effusion is when fluid collects underneath the lung and may look like an elevated hemidiaphragm. A hernia of the diaphragm can also mimic an elevated diaphragm.
In confusing cases where a list of possibilities is proposed, a ct scan be done and will be definitive. Most of the time, unfortunately the cause is not identified and the finding is chronic and does not contribute to the reason for the chest X-ray. Your clinical doctor will determine the next best course of testing based on your history and presentation.