Mediastinal tumors and masses can develop from several different tissues and organs in the center of the chest. At Saint John’s Cancer Institute and Health Center, complex cases can be evaluated by a multidisciplinary team to determine the diagnosis and develop an individualized treatment plan.
What Is the Mediastinum?
The mediastinum is the central area of the chest located between the lungs. It extends from the breastbone, or sternum, in front to the spine in back, and from the lower neck to the diaphragm. This space contains many important structures, including the heart, major blood vessels, trachea, esophagus, lymph nodes, nerves, and thymus.
A wide variety of tumors, cysts, enlarged lymph nodes, and other abnormalities can develop within the mediastinum. Some are benign, while others are cancerous. Determining exactly where a mass is located is an important first step because different types of abnormalities tend to develop in different areas of the mediastinum.
Where Do Mediastinal Tumors Develop?
Using CT and other cross-sectional imaging, physicians divide the mediastinum into three major compartments: the prevascular (anterior), visceral (middle), and paravertebral (posterior) compartments. The location of a mass, along with its appearance on imaging and a patient’s age, symptoms, and medical history, can help narrow the possible diagnosis.
Prevascular (Anterior) Mediastinal Tumors
The prevascular, or anterior, mediastinum is the area behind the breastbone and in front of the heart and major blood vessels. It contains the thymus, fat, lymph nodes, and other structures. Many mediastinal masses occur in this compartment.
Common considerations for a mass in this area include abnormalities of the thymus, lymphoma, germ cell tumors, and thyroid tissue extending into the chest. Imaging can often provide important clues, but additional testing may be needed to determine exactly what type of mass is present.
Thymoma and Thymic Carcinoma
Thymoma and thymic carcinoma are tumors that arise from cells of the thymus. Thymoma is the more common thymic tumor and can range from relatively slow-growing disease to tumors that invade nearby tissues. Thymic carcinoma is less common and generally behaves more aggressively.
Because thymic tumors can differ considerably in their behavior, treatment depends on the tumor type, extent of disease, and whether it can be completely removed. Surgery is an important treatment for many localized thymic tumors, while more advanced disease may require a combination of surgery, radiation therapy, and systemic treatment.
Lymphoma
Lymphoma is a cancer of lymphocytes, a type of white blood cell involved in the immune system. Both Hodgkin lymphoma and non-Hodgkin lymphoma can involve lymph nodes within the mediastinum, sometimes producing a large mass in the anterior chest.
Distinguishing lymphoma from other mediastinal tumors is important because treatment usually relies on systemic therapies rather than surgical removal of the mass. A tissue biopsy may therefore be needed before treatment is planned.
Germ Cell Tumors
Germ cell tumors are uncommon tumors that can develop in the mediastinum, particularly in the anterior compartment. They include several different tumor types that can be benign or malignant and may occur even though the reproductive organs are normal.
Imaging, blood tests for specific tumor markers, and sometimes biopsy can help determine the type of germ cell tumor and guide treatment.
Substernal Goiter and Thyroid Masses
The thyroid gland is located in the lower neck, but an enlarged thyroid, or goiter, can extend downward into the chest and appear as a mediastinal mass. This is called a substernal or intrathoracic goiter.
CT imaging can help determine how far the thyroid extends into the chest and whether it is affecting the trachea, blood vessels, or other nearby structures. Treatment depends on symptoms, size, anatomy, thyroid function, and other clinical findings.
Visceral (Middle) Mediastinal Masses
The visceral, or middle, mediastinum contains structures including the trachea, esophagus, heart, major blood vessels, and lymph nodes. Abnormalities in this area can include enlarged lymph nodes, congenital cysts, and other lesions arising from structures within the central chest.
Bronchogenic Cysts
Bronchogenic cysts are congenital abnormalities that develop during formation of the respiratory system before birth. They are usually fluid-filled and are often discovered incidentally on imaging performed for another reason.
Some bronchogenic cysts never cause problems, while others can enlarge, become infected, or press on the airway or other nearby structures. CT or MRI can help characterize the cyst and its relationship to surrounding anatomy. Treatment is individualized based on symptoms, imaging findings, location, and the potential for complications.
Pericardial Cysts
Pericardial cysts are uncommon, usually benign fluid-filled abnormalities that develop near the membrane surrounding the heart. Many cause no symptoms and are discovered incidentally during chest imaging.
Observation may be appropriate for some patients, while additional evaluation or treatment may be considered when a cyst causes symptoms, changes over time, has uncertain imaging features, or affects nearby structures.
Other Mediastinal Cysts
Other congenital cysts can develop in association with the airway, esophagus, and surrounding structures. Their significance depends on their size, location, appearance, symptoms, and relationship to nearby organs. Some can be monitored, while others may be removed when they cause symptoms, create complications, or cannot be confidently characterized with imaging.
Paravertebral (Posterior) Mediastinal Tumors
The paravertebral, or posterior, mediastinum is the area along the thoracic spine. Masses in this region frequently arise from nerves or tissues surrounding the spine, although other abnormalities can also occur.
Neurogenic Tumors
Neurogenic tumors arise from nerves or nerve-related tissues and are among the characteristic tumors found in the posterior mediastinum. In adults, many are benign, although malignant tumors can also occur.
CT and MRI can help determine the tumor’s location and whether it extends toward the spinal canal or involves nearby structures. Treatment depends on the type of tumor, symptoms, imaging characteristics, and whether there is concern for growth or malignancy.
Symptoms of Mediastinal Tumors
Many mediastinal tumors and masses cause no symptoms and are discovered unexpectedly during a chest X-ray, CT scan, or other imaging performed for a different reason. When symptoms do occur, they often result from the mass pressing on or affecting nearby structures within the chest.
Symptoms can vary depending on the size, location, and type of mass and may include:
- Cough
- Shortness of breath
- Wheezing or noisy breathing
- Chest pain or pressure
- Difficulty swallowing
- Hoarseness
- Coughing up blood
- Swelling of the face, neck, or upper body
- Fever or chills
- Night sweats
- Unexplained weight loss
- Fatigue
These symptoms can occur with many conditions other than a mediastinal tumor. Persistent or unexplained symptoms should be evaluated so that the underlying cause can be identified.
Diagnosis of Mediastinal Tumors
Evaluating a mediastinal mass begins with determining exactly where it is located, what structures are involved, and what type of tumor or other abnormality it may represent. CT imaging is often central to this evaluation, while MRI, PET/CT, blood tests, or other studies may provide additional information depending on the suspected diagnosis.
Not every mediastinal mass requires a biopsy before treatment. Some masses have imaging characteristics and a clinical presentation that strongly suggest a particular diagnosis. In selected patients with a mass that appears to be a completely removable thymic tumor, for example, surgery may provide both the diagnosis and treatment. Other conditions, particularly lymphoma and some germ cell tumors, usually require a specific diagnosis before treatment is started.
CT Scan
A CT scan provides detailed images of the mediastinum and helps physicians determine the size and location of a mass and its relationship to the heart, major blood vessels, airways, lungs, and other nearby structures. Contrast-enhanced CT can provide additional information about blood vessels and the characteristics of the mass.
MRI
MRI can provide additional detail when physicians need to evaluate soft tissues, blood vessels, the spine, or possible involvement of nearby structures. It can be particularly helpful for selected cystic lesions and masses near the spine or other complex anatomy.
PET/CT
PET/CT may be used when certain cancers are suspected or have already been diagnosed. It can help evaluate metabolic activity within a mass and identify disease elsewhere in the body, although not every mediastinal mass requires PET/CT.
Blood Tests and Tumor Markers
Blood tests may help evaluate certain types of mediastinal tumors. When a germ cell tumor is suspected, physicians may measure tumor markers such as alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (beta-hCG). Other laboratory tests may be ordered based on the type of mass being considered and the patient’s overall health.
When Is a Biopsy Needed?
A biopsy removes cells or tissue so they can be examined by a pathologist. Whether a mediastinal mass should be biopsied—and how the biopsy should be performed—depends on its location, imaging characteristics, suspected diagnosis, and proximity to important structures.
Planning the biopsy before the procedure is particularly important. Different diseases require different amounts and types of tissue, and the safest approach should also preserve future treatment options. The goal is to obtain enough tissue for an accurate diagnosis while avoiding unnecessary procedures.
Image-Guided Needle Biopsy
A needle biopsy may be performed using CT or other imaging to guide the needle safely into a mediastinal mass. Tissue samples are then examined by a pathologist. This approach may be appropriate when the mass can be safely reached through the chest wall and adequate tissue can be obtained.
Endobronchial Ultrasound (EBUS)
Endobronchial ultrasound combines bronchoscopy with ultrasound imaging to evaluate structures and lymph nodes next to the trachea and major airways. A needle can be passed through the airway wall to obtain samples without making an incision in the chest.
EBUS can provide a diagnosis for many centrally located mediastinal abnormalities and lymph nodes. Whether it is the best biopsy method depends on the location of the abnormality and the amount and type of tissue needed for diagnosis.
Mediastinoscopy
Mediastinoscopy is a surgical procedure that allows a thoracic surgeon to reach lymph nodes and other structures in the central mediastinum through a small incision near the base of the neck. It can obtain larger tissue samples when less invasive techniques are not appropriate or have not provided enough tissue for diagnosis.
Anterior Mediastinotomy
An anterior mediastinotomy, sometimes called a Chamberlain procedure, provides surgical access to selected masses or lymph nodes in the anterior chest that cannot be adequately reached with other biopsy techniques. It is used selectively as newer minimally invasive and image-guided approaches have expanded the options for obtaining tissue.
Surgical Biopsy
In selected cases, minimally invasive thoracic surgery may be used to obtain a larger tissue sample or remove a mediastinal mass. Video-assisted thoracic surgery (VATS) or robotic-assisted surgery can provide access to areas that may be difficult to reach with a needle or bronchoscope.
Choosing the Right Diagnostic Approach
There is no single biopsy procedure that is appropriate for every mediastinal mass. Physicians consider the location and appearance of the mass, the diseases most likely to cause it, whether sufficient tissue can be obtained safely, and whether surgery may already be the appropriate treatment.
For example, a mass that strongly resembles a localized, removable thymic tumor may proceed directly to surgical resection without a separate preoperative biopsy. When lymphoma is suspected, obtaining enough tissue to accurately classify the lymphoma is particularly important because treatment generally relies on systemic therapy rather than surgical removal of the mass.
A multidisciplinary approach can help coordinate imaging, pathology, pulmonology, thoracic surgery, medical oncology, and radiation oncology when needed so that the diagnostic procedure supports—not complicates—the eventual treatment plan.
Imaging Tests for Mediastinal Tumors
Imaging plays a central role in evaluating mediastinal tumors and masses. In addition to showing where a mass is located, imaging can help physicians determine whether it appears solid or cystic, whether it contains fat or other characteristic features, and whether it involves nearby organs, blood vessels, airways, or other structures.
The appearance and location of a mediastinal mass can sometimes strongly suggest a particular diagnosis and help determine whether additional imaging, blood tests, biopsy, or surgical evaluation is appropriate.
Chest X-Ray
A mediastinal mass may first be discovered unexpectedly on a chest X-ray performed for another reason. An X-ray can show widening or an abnormal contour within the mediastinum, but it generally cannot characterize a mass with the detail provided by CT or MRI.
Computed Tomography (CT)
CT is one of the primary imaging tests used to evaluate a mediastinal mass. It provides detailed cross-sectional images that show the mass’s size, location, internal characteristics, and relationship to the heart, lungs, major blood vessels, airway, and other nearby structures.
When appropriate, intravenous contrast can help physicians evaluate blood vessels and distinguish the mass from surrounding tissues. CT findings can also help determine whether a mass may be safely biopsied and which approach could provide the best access.
Magnetic Resonance Imaging (MRI)
MRI provides detailed images of soft tissues and can be particularly useful when evaluating masses near the spine, nerves, heart, or major blood vessels. It may also help characterize certain cystic abnormalities or clarify whether a tumor involves nearby structures.
PET/CT
PET/CT may be used for selected mediastinal tumors when physicians need additional information about the activity or extent of disease. It can help evaluate some cancers for involvement of lymph nodes or other areas of the body, but it is not necessary for every mediastinal mass.
How Are Mediastinal Tumors Staged?
There is no single staging system for all mediastinal tumors because the mediastinum can contain many different types of cancer. Staging begins after physicians determine what type of tumor is present. A thymic tumor, lymphoma, germ cell tumor, or cancer involving another organ is staged according to the system established for that particular disease.
In general, cancer staging describes how extensive a cancer is, including the size or local extent of the primary tumor, whether nearby structures or lymph nodes are involved, and whether cancer has spread to other parts of the body. This information helps physicians select the most appropriate treatment and provides important information about prognosis.
Staging Thymoma and Thymic Carcinoma
Thymoma and thymic carcinoma are thymic epithelial tumors that develop in the anterior mediastinum. These tumors are staged using a TNM system that considers the extent of the primary tumor (T), whether cancer has spread to regional lymph nodes (N), and whether there are pleural, pericardial, or distant metastases (M).
Earlier-stage thymic tumors are generally confined to the thymus or nearby tissues, while more advanced stages involve progressively greater extension into structures within the chest, lymph nodes, the lining around the lungs or heart, or distant parts of the body.
Stage I Thymic Tumors
Stage I thymic epithelial tumors are localized and have not spread to regional lymph nodes or distant sites. The current TNM system also considers tumor size within this stage.
Stage II Thymic Tumors
Stage II tumors have directly involved certain nearby structures, such as the pericardium, lung, or phrenic nerve, but have not spread to regional lymph nodes or distant sites.
Stage III Thymic Tumors
Stage III disease is divided according to which structures the tumor has invaded. This may include the chest wall, major veins or pulmonary blood vessels, or, in more locally advanced disease, structures such as the aorta, heart muscle, trachea, or esophagus.
Stage IV Thymic Tumors
Stage IV thymic tumors have spread beyond the primary tumor in specific ways. This can include spread to regional lymph nodes, separate tumor deposits along the pleura or pericardium, involvement of deeper lymph nodes, or distant metastases elsewhere in the body.
Why Accurate Staging Matters
Stage is only one part of treatment planning. Physicians also consider the exact tumor type, whether the mass can be completely removed, its relationship to critical structures, the patient’s overall health, and whether surgery, radiation therapy, systemic therapy, or a combination of treatments is most appropriate.
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