Non-cancerous tumours of the thymus

A non-cancerous (benign) tumour of the thymus is a growth that does not spread (metastasize) to other parts of the body. Non-cancerous tumours are not usually life-threatening. They may be removed with surgery and do not usually come back (recur). Non-cancerous tumours of the thymus are rare.

There are a few types of non-cancerous tumours of the thymus.

A thymic cyst is a sac filled with fluid that is within the thymus or made up of thymus tissue. It is found in the mediastinum or neck.

A thymic cyst can be congenital or acquired.

• Congenital thymic cysts are present at birth. They usually have only a single space of fluid.
• Acquired thymic cysts can happen along with thymomas or other tumours of the thymus. They can also happen after a thoracotomy or after radiation therapy for Hodgkin lymphoma. Most acquired thymic cysts have many small spaces of fluid within a cyst.

Thymic cysts don’t usually cause any symptoms. They are often found when an imaging test is done for other health reasons.

Surgery may be used to remove a thymic cyst, especially when it is associated with cancer such as thymoma or lymphoma.

A thymolipoma is a tumour of the front mediastinum made up of fat and thymus tissue. It tends to grow slowly, but can get to be very large.

Most thymolipomas don’t cause any symptoms. They are usually found when an imaging test is done for other health reasons. If a thymolipoma grows very large, it may cause coughing, trouble breathing and chest pain.

Treatment for thymolipoma may be surgery to remove the tumour.

Thymic hyperplasia is an abnormal growth of the thymus and the thymus becomes enlarged. It is often described with other non-cancerous tumours of the thymus, but it is not an actual tumour.

Thymic hyperplasia is associated with myasthenia gravis and other autoimmune diseases. It may happen in children with Hodgkin lymphoma after chemotherapy.