Definition of SVC obstruction:

SVC obstruction is a narrowing or blockage of the superior vena cava -- the second largest vein in the human body. The superior vena cava moves blood from the upper half of the body to the heart.

Causes, incidence, and risk factors:

Superior vena cava (SVC) obstruction is a relatively rare condition.

Most often it is caused by cancer or a tumor in the mediastinum (the area of the chest under the breastbone and between the lungs).

The types of cancer that can lead to this condition include:

• Breast cancer
• Lymphoma
• Metastatic lung cancer (lung cancer that spreads)
• Testicular cancer
• Thyroid cancer
• Thymic tumors

Superior vena cava obstruction can also be caused by noncancerous conditions that cause scarring. These conditions include:

• Histoplasmosis infection
• Inflammation of a vein ( thrombophlebitis)
• Lung infections (such as tuberculosis)

Other causes of superior vena cava obstruction include:

• Aortic aneurysm
• Blood clots in the superior vena cava
• Constrictive pericarditis
• Enlargement of the thyroid gland (goiter)

Catheters placed in the large veins of the upper arm and neck may cause blood clots in the superior vena cava.