The mediastinum is the compartment of the chest between the lungs. The anterior mediastinum is the part closest to the sternum or breast bone. The anterior mediastinum is below the collar bone and extends 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.
What does the normal anterior mediastinum look like?
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. This is a an area where in normal cases, not much is going on other than a bit of thymus gland.
Thymic tissue in the anterior mediastinum
This is normally present and gradually diminishes in size with age. There is often fat within the remaining gland as we get older. Sometimes the remaining gland can be larger then expected for age, nodular or even mass like. This can present diagnostic challenges.
Symptoms of anterior mediastinal mass
These are often not helpful in reaching a specific diagnosis but tell us something may be going on in the chest. Patients can have cough, shortness of breath, coughing up blood, fever, chills, and chest pain.
Anterior mediastinal mass differential diagnosis
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 cyst, carcinoma, carcinoid and so on. The gland can also enlarge and this is called hyperplasia.
Enlarged lymph nodes can be seen with lymphoma which is a cancer of the lymphatic system. Lymph nodes can also enlarge for other reasons such as infection or spread of cancer from other locations in the body.
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.
Soft tissue density in the anterior mediastinum
This tells us that there is soft tissue in the anterior mediastinum. Soft tissue refers to the consistency of the tissue. The tissue does not represent bone, fat, fluid or air. It is similar in consistency to muscles. This does not tell us a specific diagnosis on its own.
Imaging appearance of anterior mediastinal mass
The radiologist can sometimes 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 in the lower neck. 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.
Many tumors of the anterior mediastinum will not have any features which allow a specific diagnosis.
How can we know if the mass is cancer?
A cancer or 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. Often a biopsy will be needed to confirm the diagnosis.
What further testing is needed for diagnosis?
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.
Anterior mediastinal mass: summary
Anterior mediastinal masses can vary from benign cysts to aggressive cancers. Normal structures such as the thymus gland can enlarge and sometimes cause diagnostic challenges. Imaging will play an important role in diagnosis and directing the next steps.