The mediastinum is the space between your lungs in the chest. The mediastinum has blood vessels, lymph nodes, fatty tissue, nerves and other structures. The mediastinum is between the lungs on a chest x ray as a white area.
Sometimes the mediastinum is described as widened by the radiologist. This can be caused by many different things and your medical history is often helpful. Some of the causes are benign such as more than usual fat accumulation. Other more concerning causes can include bleeding after trauma, tumors, and aneurysms.
The radiologist sees this finding as a widening of the space between your lungs. This is a subjective finding which the radiologist often bases on his experience of looking at thousands of prior chest x rays. Sometimes there are clues to the cause of this appearance, but in most cases, a chest CT is needed to look further. A chest x ray does not provide any details, just a white widened space. The chest CT allows a look inside.
Your history is often helpful. Say for instance you had a bad car accident, then bleeding becomes a concern. In other cases, a lumpy and bumpy contour of the widening suggests that big lymph nodes and cancer may be a cause. If you are a heavy set person, then the appearance may simply be because of fat accumulation. Another dangerous condition can be an aneurysm of the aorta, which passes through the mediastinum. Other masses of the mediastinum which can originate from lymph nodes or other structures can also cause a widened contour either on one side or throughout.
In all cases, a discussion with your physician is essential to better determine the cause and therapy. This is a finding in which the history and physical exam findings are especially important. For example, a widened mediastinum after a car accident may indicate potentially lethal bleeding. Night sweats, fatigue, weight loss may indicate cancer. A well feeling patient without complaints may indicate the finding is due to fat accumulation or even the technique taken for the x ray. It is therefore important to have your doctor closely evaluate you when this finding is described in a chest x ray.