Webster's New World Medical Dictionary

stem cell transplantation
The use of stem cells
as a treatment for cancer or other illness. The stem
cells are removed (or obtained from a donor) first.
Before the transplant is done, the patient receives
high-dose chemotherapy and/or radiation therapy
to destroy diseased cells. Then the stem cells are
returned to the patient, where they can produce new
blood and immune cells and replace the cells
destroyed by the treatment. The stem cell prepara-
tion is infused into a vein and, once in the blood-
stream, the stem cells migrate to the bone marrow
space.
stenosis
A narrowing. For example, aortic steno-
sis is a narrowing of the aortic valve in the heart.
stenosis, pulmonary
See 
pulmonary stenosis.
stent
A tube designed to be inserted into a vessel
or passageway to keep it open. Stents are inserted
into narrowed coronary arteries to help keep them
open after balloon angioplasty. The stent then allows
the normal flow of blood and oxygen to the heart.
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stent
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Stents placed in narrowed carotid arteries (the ves-
sels in the front of the neck that supply blood to the
brain) appear useful in treating patients at elevated
risk for stroke. Stents are also used in other struc-
tures such as the esophagus to treat a constriction,
the ureters to maintain the drainage of urine from
the kidneys, and the bile duct to keep it open.
stereotactic
Referring to precise positioning in
three-dimensional space. For example, biopsies, sur-
gery, or radiation therapy can be done stereotactically.
stereotactic needle biopsy
See 
biopsy, stereo-
tactic needle.