Thymoma and Myasthenia Gravis Tumors

The thymus gland is located behind the upper sternum (breast bone) and in front of the heart. It is made up primarily of fatty tissue, white blood cells (lymphocytes), and stromal (epithelial) cells.

The thymus plays an important role in the body’s immune system, producing T lymphocytes (T cells) which are vital to being able to fight infection or foreign bodies. The thymus is at its largest size and greatest activity in infancy and childhood, then shrinking (atrophying) and becoming less functional in adulthood when the gland consists mostly of fatty tissue.

Malfunction of the thymus gland may play a role in the development of some autoimmune diseases which are caused by a hyperactive immune system which attacks the host organism (self).

Two primary tumors originate in the thymus:

Thymomas are derived from the epithelial cells of the thymus gland and may be benign or malignant. Thymomas have been associated with a variety of autoimmune disorders. 15-20% of patients with myasthenia gravis have thymomas.

Other less common associated conditions include:

• red cell aplasia,
• hypogammaglobulinemia
• polymyositis
• systemic lupus erythematosus
• rheumatoid arthritis
• Sjogren syndrome
• thyroiditis

Because of their malignant potential, surgical removal of thymomas is generally advised. Patients with extraocular myasthenia gravis, even without a thymic tumor, have been shown to respond favorably to removal of the thymus gland (thymectomy). Thymic cancer is very rare (only 1.5 cases for every million people) and is more difficult to eradicate than thymomas.

Lymphomas may originate from the lymphocytes of the thymus gland. In the past, very young children with an enlarged thymus gland were often treated with radiation to shrink the gland. As adults, these patients have an increased risk for the development of thyroid cancer and thymic lymphoma.

Symptoms of Thymoma and Myasthenia Gravis

Symptoms of thymoma or thymic cancer may include:

• persistent cough
• chest pain or pressure
• shortness of breath
• muscle weakness
• double vision or drooping eyelids
• swelling of the face or arms
• difficulty swallowing

However, thymoma and thymic cancer do not always present with symptoms. Sometimes these tumors can only be detected with an X-ray.

Diagnosis of Thymoma and Myasthenia Gravis

A careful medical history and physical examination may indicate the risk of thymoma or thymic cancer.

A biopsy is a procedure in which a pathologist examines under a microscope a sample of tissue or cells. A number of different types of biopsies are available, including:

• fine needle aspiration (FNA) biopsy
• core needle biopsy (which removes a larger "core" of tissue than a fine needle)
• incisional biopsy (removal of a piece or part of tissue)
• excisional biopsy (removal of the entire abnormality)

Thymomas have a tendency to spread if their surrounding capsule is violated during either a biopsy attempt or an operation to remove them. For this reason, when there is a strong suspicion of a thymoma, its complete removal, rather than a needle, core or incisional biopsy, is recommended.

A mediastinoscopy and biopsy involves the insertion of a scope behind the sternum (breast bone), and its advancement into the mediastinum, the central portion of the chest cavity. Samples of mediastinal lymph nodes or tumor deposits can be obtained. Some mediastinal lymphomas can be diagnosed using mediastinoscopy. This procedure requires general anesthesia and a small incision at the base of the neck just above the breast bone.

Commonly used imaging studies to evaluate tumors of the thymus gland include:

• Chest X-rays, which depict the interior of the chest but often fail to show the thymus gland which is hidden behind the sternum (breast bone)
• Computed tomography (CT-scans), which produce a series of images of the inside of the body taken at different depths and angles, to reveal a higher level of detail than provided by chest x-rays. . To ensure that your blood vessels and organs show up clearly in these scans, dye may be swallowed or injected into a vein when the CT scan is being performed
• Magnetic Resonance Imaging (MRI scan) in which detailed images of the internal organs and tissues are created using a magnetic field, radiowaves, and a computer.
• Position Emission Tomography (PET scan), which determines how the body is using glucose. Every cell in the body takes in glucose in order to function normally. Tumor cells are often metabolically active (growing faster than normal cells) and therefore take up more glucose. With a PET scan, small amount of radioactive glucose is injected into a vein. The scanner then revolves around the body, identifying areas where glucose uptake is the greatest, often sites of tumor or tumor spread. Areas of increased glucose uptake (brightness) detected with a PET scan may indicate malignancy but can also be caused by inflammation or infection.

Prior to any major chest operation, the ability of the patient to tolerate the procedure is often evaluated. Pulmonary Function Tests (PFTs) assess the function and strength of the lungs. For the most common of these, after forcefully blowing air into a tube, a machine called a spirometer measures the volume of air that the patient is able to hold in the lungs, and the speed with which it can be blown out (exhaled).

Surgical Approaches forThymoma and Myasthenia Gravis

Removal of the thymus gland is called a thymectomy. A variety of operative approaches, often dictated by the size and location of the tumor, are used to remove thymomas and thymic cancers.

• Median sternotomy - dividing the sternum (breast bone) in the midline to gain access to the mediastinum behind and allow partial or complete removal of the tumor.
• Thoracotomy - an incision in the side or back between the ribs to provide access to the chest cavity.
• Video-assisted thoracic surgery (VATS) - use of a small camera and specially designed small instruments inserted between the ribs to work inside the chest and remove tissue while avoiding a thoracotomy.
• Robotic-assisted thoracic surgery - uses a robotic device and a computer to maneuver surgical instruments inserted between the ribs and inside the chest as with VATS. But this device allows surgeons to operate with even greater dexterity through small incisions.