The mediastinum is the compartment of the chest between the lungs. The anterior mediastinum is the part closest to the sternum or breast bone and below the collar bone extending down to the covering of the heart. Abnormalities of this compartment of the chest can be predicted based on the contents which include: the thymus, lymph nodes and in abnormal cases, an enlarged thyroid gland.
On CT, the appearance of the anterior mediastinum often depends on the age but there is overlap. The thymus gland often becomes smaller and smaller as we age, becoming nearly all fat as we get into our 40s and beyond. The lymph nodes are usually small or not visible in normal cases. The thyroid gland is usually confined to the neck in normal cases. This is a an area where in normal cases, not much is going on other than a bit of thymus gland.
In abnormal cases, a mass or enlarged lymph nodes are found. The appearance of the mass will allow the radiologist to suggest a diagnosis or at least narrow it to some of the more likely possibilities. For example, there are many different kinds of masses that originate from the thymus gland such as hyperplasia, cyst, carcinoma, carcinoid and so on.
Enlarged lymph nodes can be seen with lymphoma which is a cancer of the lymphatic system. Primitive or stem cells can lead to germ cell tumors in the anterior mediastinum. Enlarged thyroid gland called a goiter can extend to the anterior mediastinum. Other masses of the thyroid gland and parathyroid glands can be found in this location. Sometimes an aneurysm of the aorta can extend into this location as well.
The radiologist can often make a specific diagnosis or at least suggest the most likely possibility based on the appearance. For example, a thymic cyst will look like a walled off fluid collection. A thyroid goiter will be seen extending from the thyroid gland. Lymphoma will often have discrete enlarged nodes.
One of the more common germ cell tumors called a teratoma will have different tissues such as fat, calcification, soft tissue, teeth or bone which will give it a characteristic appearance on CT. An aneurysm will be arising directly from the aorta. An aggressive mass will be one that is seen invading other areas of your chest or with spread to other areas such a lymph nodes or bone.
More testing may be needed such as a pet scan, biopsy or even surgery. In all cases, your doctor will need to evaluate your history, blood tests and any other information to come up with the most accurate diagnosis and treatment plan. The range of possibilities is a very wide in this area of the chest. The radiologist will play an important role in diagnosis and directing the next steps.