What is the mediastinum?
Anterior mediastinal 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.
Middle mediastinal masses
- 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.
Posterior mediastinal masses
- 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 tumor
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).
Almost 40% of people who have mediastinal tumors experience no symptoms. Most are found when a chest x-ray is performed for another reason.
- Shortness of breath
- Chest pain or fullness
- Night sweats
- Coughing up blood
- Weight loss
- Chest x-ray: not very specific, but leads to further testing
- Computed tomography (CT) scan of the chest: the appearance of the mass suggests what the diagnosis is
- Magnetic resonance imaging (MRI) of the chest: may help define the relationship of mediastinal masses to
The tests most commonly used to diagnose and evaluate a mediastinal tumor include:
- Blood Tests:
- Alpha feto protein (AFP), beta HCG, LDH
- Tissue Biopsy
- 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
Type Histologic description
A Tumor in which foci having features of type A thymoma are admixed with foci rich in lymphocytes
B1 Tumor resembles normal functional thymus; combines large expanses having an appearance practically indistinguishable from that of normal thymic cortex with areas resembling thymic medulla
B2 Tumor in which neoplastic epithelial component appears as scattered plump cells with vesicular nuclei and distinct nucleoli among a heavy population of lymphocytes; perivascular spaces are common and sometimes very prominent; a perivascular arrangement of tumor cells resulting in a palisading effect may be seen.
B3 Thymoma predominantly composed of epithelial cells having a round or polygonal shape and exhibiting no or mild atypia; they are admixed with a mild component of lymphocytes, resulting in a sheetlike growth of the neoplastic epithelial cells
C Thymic tumor exhibiting clear-cut cytologic atypia and a set of cytoarchitectural features no longer specific to the thymus, but rather analogous to those seen in carcinomas of the other organs; type C thymomas lack immature lymphocytes; whatever lymphocytes may be present are mature and usually admixed with plasma cells
The treatment of mediastinal cancers depends on the type of tumor and its location:
- Usually treated with resection. Earlier stage tumors need no chemotherapy or radiation. More advanced tumors are treated with preoperative treatment to shrink the tumors before an operation. If the final pathology report shows the thymoma is stage 3w, then post-op chemotherapy and radiation treatment are often recommended.
- Surgery: Traditionally, removal of the thymoma required a median sternotomy (8-inch incision made on the front of the chest). It is the standard incision used for heart surgery. We usually do minimally invasive surgery to remove thymomas 6 cm (2.5 in) or less.
- Are treated with chemotherapy or chemotherapy and radiation.
- The role of surgery is to make a diagnosis by mediastinotomy or mediastinoscopy
- In the posterior (back) mediastinum are treated surgically.
Benefits of minimally invasive surgery for mediastinal tumors
Compared to open surgery, minimally invasive surgery, such as video-assisted thoracoscopy (VATS) mediastinoscopy, offers patients:
- Decreased postoperative pain
- Shorter hospital stay
- More rapid recovery and return to work
Possible complications of minimally invasive surgical treatment include:
- Damage to the surrounding structures ( heart, pericardium (sac around the heart) or nerves (Phrenic or recurrent laryngeal causing hoarseness