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Mediastinal Tumors

Mediastinal tumors

Definition

A mediastinal tumor is a growth in the central chest cavity (mediastinum), which separates the lungs and contains the heart, aorta, esophagus, thymus, and trachea. Mediastinal tumors are also known as neoplasms of the mediastinum.

Description

Growths that originate in the mediastinum are called primary mediastinal tumors. Most of them are composed of reproductive (germ) cells or develop in thymic, neurogenic (nerve), lymphatic, or mesenchymal (soft) tissue.

Secondary (metastatic) mediastinal tumors originate in the lung, stomach, esophagus, and trachea, and spread through the lymphatic system to the chest cavity.

Although still relatively rare, malignant mediastinal tumors are becoming more common. Usually diagnosed in patients between 30 and 50 years old, they can develop at any age and arise from any tissue that exists in or passes through the chest cavity.

The mediastinum is traditionally divided into superior, anterior, middle, and posterior compartments, and is also described as having anterosuperior, middle, and posterior divisions. Boundaries of these divisions are not fixed, and they frequently overlap.

The anterosuperior compartment contains a vein and the thymus gland, superior vena cava, aortic arch, and thyroid gland. More than half (54%) of mediastinal tumors in adults and 43% of those in children occur in the anterosuperior compartment.

The middle mediastinum contains the pericardium, heart, nerves of the diaphragm (phrenic nerves), trachea, main bronchial stem, and lung hila. Twenty percent of adult mediastinal tumors and 18% of those in children occur in this division.

The posterior mediastinum contains the sympathetic chain, vagus nerve (which controls the heart, larynx, and gastrointestinal tract), thoracic duct (which drains lymph from the abdomen, legs, and left side of the head and chest), descending thoracic aorta, and the esophagus. Slightly more than one fourth (26%) of adult mediastinal tumors and 40% of those in children occur in the posterior mediastinum.

Each of these compartments also contains lymph nodes and fatty tissue.

Types of cancers

Anterior mediastinal tumors

The most common anterior mediastinal tumors are thymomas, teratomas, lymphomas, and thyroid tissue that has become enlarged or displaced (ectopic).

THYMOMAS.

The cause of most adult mediastinal tumors and 15% of those in children, thymomas almost always form at the spot where the heart and great vessels meet. These tumors usually develop between the ages of 40 and 60.

Mediastinal tumors
Cancer type Occurs in
Thymomas Anterior mediastinum, almost always form where heart and major vessels meet
Teratomas Anterior mediastinum, along the center of the body between the skull and kidneys
Lymphomas Anterior and middle mediastinum
Thyroid tumors Thyroid (anterior mediastinum)
Mesenchymal tumors (soft tissue tumors) Middle mediastinum
Carcinomas Middle mediastinum
Neurogenic tumors (developing in nerve cells) Posterior mediastinum
Malignant schwannomas Posterior mediastinum
Neuroblastomas Posterior mediastinum

About half of the people who have thymomas do not have any symptoms. Between 35 and 50% experience symptoms of myasthenia gravis , such as

  • weakness of the eye muscles
  • drooping of one or both eyelids (ptosis)
  • fatigue

Early treatment of these slow-growing tumors is very effective. Most are benign, but thymomas can metastasize and should always be considered cancerous.

TERATOMAS.

Most common in young adults, teratomas are made up of embryonic (germ) cells that did not develop normally and do not belong in the part of the body where the tumor is located. Found along the center of the body between the skull and kidneys, teratomas account for:

  • 10%-15% of primary mediastinal tumors
  • 70% of germ cell tumors in children
  • 60% of germ cell tumors in adults

Teratomas may be solid or contain cysts. Malignant teratomas usually develop between the ages of 30 and 40, and almost all (90%) of them occur in men.

At least 90% of patients with these tumors experience:

  • chest pain
  • cough
  • fever
  • shortness of breath

but these symptoms may not appear until the tumor has grown very large.

LYMPHOMAS.

These tumors account for 10-20% of anterior mediastinal tumors. Although lymphomas are the second most common mediastinal tumor in children, they are usually diagnosed between the ages of 30 and 40. Nonsclerosing Hodgkin's disease causes most adult mediastinal lymphomas.

Some patients with lymphomas do not have symptoms. Others cough or experience chest pain.

THYROID TUMORS.

Most mediastinal thyroid tumors grow out of goiters and occur in women between the ages of 50 and 60. About 75% of these tumors extend to the windpipe (trachea). The rest extend behind it.

Mediastinal thyroid tumors are encapsulated and do not metastasize.

Middle mediastinal tumors

Tumors of the middle mediastinum include lymphomas, mesenchymal tumors, and carcinomas.

MESENCHYMAL TUMORS.

Also called soft tissue tumors, mesenchymal tumors originate in connective tissue within the chest cavity. These tumors account for about 6% of primary mediastinal tumors. More than half (55%) of them are malignant.

The most common mesenchymal tumors are lipomas, liposarcomas, fibromas, and fibrosarcomas.

Posterior mediastinal tumors

Tumors of the posterior mediastinum include: neurogenic tumors, mesenchymal tumors, and endocrine tumors.

NEUROGENIC TUMORS.

Representing 19%-39% of mediastinal tumors, neurogenic tumors can develop at any age. They are most common in young adults.

Adult neurogenic tumors are usually benign. In children, they tend to be malignant and tend to metastasize before symptoms appear.

MALIGNANT SCHWANNOMAS.

Also known as: malignant sheath tumors, malignant sarcomas, and neurosarcomas, these tumors develop from the tube (sheath) enclosing the peripheral nerves that transmit impulses from the central nervous system (CNS) to muscles and organs.

Usually large and painful, these rare, aggressive tumors may invade the lungs, bones, and aorta.

NEUROBLASTOMAS.

The most common malignant tumors of early childhood, neuroblastomas generally occur before the age of two. These tumors usually develop in the adrenal glands, neck, abdomen, or pelvis.

Neuroblastomas often spread to other organs. Most patients have symptoms that relate to the part of the body the tumor has invaded. Likelihood of survival is greatest in patients who are less than a year old and whose tumor has not spread.

Symptoms

About 40% of people who have mediastinal tumors do not have any symptoms. When symptoms exist, they usually result from pressure on an organ that the tumor has invaded, and indicate that the tumor is malignant.

The symptoms most commonly associated with mediastinal tumors are:

  • chest pain
  • cough
  • shortness of breath

A person who has a mediastinal tumor may be hoarse, cough up blood (hemoptysis ), or have:

  • fatigue
  • difficulty swallowing (dysphagia)
  • night sweats
  • systemic lupus erythematosus
  • inflamed muscles (polymyositis)
  • ulcerative colitis
  • rheumatoid arthritis
  • thyroid problems (thyroiditis, thyrotoxicosis,)
  • fever
  • glandular disorders (panhypopituitarism, adenopathy)
  • high blood pressure
  • low blood sugar (hypoglycemia)
  • breast development in males (gynecomastia)
  • wheezing
  • vocal cord paralysis
  • heart problems (superior vena cava syndrome , pericardial tamponade, arrhythmias)
  • neurologic abnormalities
  • weight loss

and other immune, autoimmune, and endocrine system disorders.

Blood disorders associated with these tumors include abnormally high levels of calcium (hypercalcemia ), abnormally low numbers of:

  • circulating blood cells (cytopenia)
  • normal red blood cells (pernicious anemia)
  • antibodies (hypogammaglobulinemia) and an inability to produce red blood cells (red-cell aplasia).

Diagnosis

Imaging studies

Routine x rays often detect mediastinal tumors. Doctors use computed tomography (CT) scans of the chest to determine tumor size and location, extent of disease, the tumor's relationship to nearby organs and tissues, and whether the tumor contains cysts or areas of calcification.

Magnetic resonance imaging (MRI) is more effective at clarifying the relationship between a tumor and nearby blood vessels, but is far more costly and time-consuming than CT scanning.

Other tests

Injecting radioactive substances into the patient's blood (radioimmunoassay) enables doctors to measure levels of hormones and other substances a tumor secretes and identify specific tumor types, evaluate the effectiveness of therapy, and monitor possible tumor recurrence.

Invasive procedures

Imaging studies play the most important role in initial diagnosis of mediastinal tumors, but before doctors can determine the most effective treatment for any tumor, they must know what kind of cells it contains.

Although invasive diagnostic procedures have been largely replaced by less invasive techniques (such as CT-guided percutaneous needle biopsy ), some patients still require surgery.

MEDIASTINOSCOPY.

Performed under general anesthesia, this relatively simple procedure enables doctors to accurately diagnose 80%-90% of mediastinal tumors, and 95%-100% of anterior mediastinal tumors.

Mediastinoscopy is especially useful in providing the large tissue specimens needed to diagnose lymphomas.

MEDIASTINOTOMY.

Doctors perform mediastinotomy by using a lighted tube to:

  • examine the center of the chest and nearby lymph nodes
  • remove tissue for biopsy
  • determine whether cancer has spread from the spot where it originated.

Similar to mediastinoscopy, this procedure begins with a small incision next to the breastbone, rather than in the patient's neck.

Mediastinotomy also enables doctors to examine the lymph nodes closest to the heart and lungs. Cancer that originates in the left upper lobe of the lung often spreads to these nodes.

THORACOTOMY.

Although some surgeons still perform this procedure to diagnose mediastinal tumors, thoracoscopy may be used instead in certain situations. In a thoracotomy , the physician gains access to the chest cavity by cutting through the chest wall. Thoracotomy allows for study, examination, treatment, or removal of any organs in the chest cavity. Tumors and metastatic growths can be removed, and a biopsy can be taken, through the incision. Thoracotomy also gives access to the heart, esophagus, diaphragm, and the portion of the aorta that passes through the chest cavity.

THORACOSCOPY.

This 100% accurate, minimally invasive procedure is performed under general anesthesia. Enabling the surgeon to view the entire mediastinum, thoracoscopy may be used when a mediastinal tumor touches the mediastinal pleura. However, this procedure has limited applications.

Thoracoscopy cannot be performed on a patient who has thick scar tissue.

Treatment

Doctors use surgery, radiation, and single-agent or combination chemotherapy to treat mediastinal tumors.

Thymomas

A patient whose thymoma is surgically removed (resected) has the best chance of survival. To lessen the likelihood of new tumors developing (reseeding), surgeons do not recommend biopsy, and try to remove the tumor without puncturing the capsule that encloses it.

RADIATION.

Thymomas respond well to radiation, which is used:

  • to treat all stages of disease
  • before or after surgical resection
  • to treat recurrent disease.

The course of treatment lasts three to six weeks. The most common complications of radiation therapy are formation of scar tissue in the lungs (pulmonary fibrosis), inflammation of the pericardium (pericarditis), and inflammation of the spinal cord (myelitis).

CHEMOTHERAPY.

The use of chemotherapy to treat invasive thymomas is becoming more common. One or more drugs may be administered before or after surgery. Synthetic hormones (corticosteroids ) can reverse the progression of tumors that do not respond to chemotherapy.

Teratomas

Teratomas are removed surgically. Chemotherapy and radiation are not used to treat these tumors. The prospect for long-term cure is excellent, and these tumors rarely recur.

Lymphomas

These tumors do not require surgery, except to make the diagnosis. Doctors treat them with chemotherapy and radiation.

Thyroid tumors

Doctors generally treat thyroid tumors with surgical resection, chemotherapy, and/or radiation.

Fibrosarcomas

Fibrosarcomas cannot usually be resected and do not respond well to chemotherapy.

Malignant schwannomas

Multiagent chemotherapy is used to treat these aggressive tumors, which tend to recur following surgery. The 5-year survival rate is 75%.

Neuroblastomas

Because these tumors sometimes regress spontaneously, doctors may postpone treatment if: the patient has no symptoms or the tumor is not growing.

In other cases, doctors remove these tumors even before symptoms appear. Risks associated with removing these tumors from the spinal canal include:

  • injury to the spinal cord or anterior spinal artery
  • uncontrolled bleeding in the spinal canal
  • decreased blood supply (ischemia) to tissues and organs.

See Also CT-guided biopsy; Fibrosarcoma; Neuroblastoma; Thyroid cancer

Resources

BOOKS

DeVita, Vincent T., Jr., et al, eds. Cancer: Principles & Prac tice of Oncology. 5th ed. Philadelphia: Lippincott-Raven, 1997, pp. 951-967.

OTHER

Mullen, Brian F., et al. "Anterior mediastinal masses." Virtual Hospital. Copyright 1992-2001. <http://www.vh.org/Providers/Textbooks/LungTumors/PathologicTypes/Text/AnteriorMediastinalMasses.html>. 23 July 2001.

Maureen Haggerty

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