The mediastinal is surrounded by the middle part of the chest, defined by the breastbone in front, the spine in back, and the lungs on each side. The mediastinal contains the heart, aorta, esophagus, thymus and trachea. It is divided into 3 parts: the anterior (front), middle, and posterior section (back):
Types of Masses
Thymoma: The most common anterior mass is a thymoma. There are different types of thymomas. They are generally seen on CT as a round, encapsulated mass, and rarely recur. The larger irregular masses, malignant thymic carcinomas are much more aggressive and have a much worse prognosis.
Lymphoma: is a cancer that arises in cancer-fighting cells called lymphocytes. Lymphoma usually starts in lymph nodes, the spleen or the bone marrow. Infrequently, lymphoma starts in the anterior mediastinum. There are 2 categories of lymphoma: Hodgkin’s disease and non-Hodgkin’s lymphoma.
Germ cell: A rare mediastinal mass is a germ cell a tumor. They are very rare. They are usually benign (60 to 70%) and are found in both males and females.
Thyroid mass: substernal goiter remains a significant consideration in the differential diagnosis of mediastinal masses, particularly those located in the anterior mediastinum. Substernal goiter is generally defined as a thyroid mass that has 50% or more of its volume located below the thoracic inlet.
Bronchogenic cyst: Bronchogenic cysts are congenital in nature. They are part of a spectrum of congenital abnormalities of the lung, including pulmonary sequestration, congenital cystic adenomatoid malformation, and congenital lobar hyperinflation (emphysema)
Pericardial cyst: Pericardial cysts are an uncommon benign congenital anomaly in the middle mediastinum. They represent 6% of mediastinal masses, and 33% of mediastinal cysts.
Neurogenic tumor: The most common cause posterior mediastinal tumors arise from nerves. They are usually benign, especially in adults. They are usually on the side of the backbone.
Symptoms of a Mediastinal Tumors
In general, mediastinal tumors are rare. They occur in patients aged 30 to 50 years. In children, tumors are most often found in the posterior (back) mediastinum, arising from the nerves. These mediastinal tumors are typically benign (not cancer).
Most are found when a chest x-ray is performed for another reason.
Shortness of breath
Chest pain or fullness
Coughing up blood
Diagnosis of Mediastinal Tumors
The tests most commonly used to diagnose and evaluate a mediastinal tumor include:
Alpha feto protein (AFP), beta HCG, LDH
CT-guided needle biopsy: may make the diagnosis
Mediastinoscopy: provides a sample of the tissue for the middle mediastinum. Does not help with posterior or anterior mediastinum. This is an out patient procedure under general anesthesia done through a 1-inch incision in the neck.
Anterior mediastinotomy (Chamberlain procedure): Just beside the sternum, an incision is made in the chest to get a piece of tissue from the mass.
EBUS (EndoBronchial UltraSound): is an outpatient procedure done without incisions. The tissue is obtained with a needle aspiration so only a small amount of tissue can be obtained so often enough tissue in not obtained through with a procedure.
The choice of test for diagnosis depends on the appearance on the CT scan. If an anterior mediastinal mass looks like a thymoma, the mass is usually resected if it does not look to be invading surrounding body parts. If an anterior mediastinal mass looks like lymphoma, the biopsy approach is mediastinoscopy (if nodes look involved) or anterior mediastinotomy if there is an anterior mediastinal mass and if the nodes look normal.
Modified Masaoka clinical staging of thymoma
I Macroscopically and microscopically completely encapsulated
IIA Microscopic trans capsular invasion
IIB Macroscopic invasion into surrounding fatty tissue or grossly adherent to but not through mediastinal pleura or pericardium
III Macroscopic invasion into neighboring organs (ie, pericardium, great vessels, or lung)
IVA Pleural or pericardial dissemination
IVB Lymphogenous or hematogenous metastasis
WHO histologic classification
Treatment of Mediastinum Tumor
The treatment of mediastinal cancers depends on the type of tumor and its location. Options include: