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Procedure
Petroid Sinus Venous Sampling
In this test, catheters are threaded from the groin area up to near the
pituitary gland to better determine where a suspected tumor may be.
You are allowed water only from midnight the night before
(nothing else to eat or drink). You will be given a light sedative, but will
be awake during the procedure. You will be taken to the Radiology Department
where the procedure will take place. The radiologist will place some local
anesthetic into the groin on each side over the main vein that drains blood
from each leg. Then a fine bore catheter will be passed up the vein, past
the heart and into the major vein in the neck (the jugular vein). From there
it is passed into a smaller vein that drains blood directly from the
pituitary gland, known as the inferior petrosal sinus. The procedure is
repeated for the other side. X-ray screening guides the radiologist to know
where the catheters are positioned. A small butterfly needle is inserted
into an arm vein.
Once the catheters are in place, blood samples will be taken from the right
and left petrosal sinus, and an arm vein at exactly the same time. After two
baseline samples, a hormone called CRH is injected into the arm vein. This
increases ACTH when a pituitary gland
tumor is present, but has no effect on ectopic
ACTH production. Further blood samples are taken for another 10 to 15
minutes, then the catheters are withdrawn. Pressure is applied to the groins
to minimize bruising. Often sampling is continued from the arm vein only,
for a total of 90 minutes. You will have to remain lying on your back for at
least 2 hours afterwards.
This test relies on the fact that if the source
of your high ACTH is the pituitary gland blood levels taken from very near
the gland will be higher than the blood level in an arm vein. Pituitary
gland tumors are often tiny and can't be seen even with the most modern
scanners. This test will help your endocrinologist to know with almost 100%
certainty whether the pituitary gland is the source or if a search is needed
elsewhere (for example in the lungs or abdomen). This guides treatment, for
example the recommendation for Pituitary surgery.
This procedure is very safe when performed by an
experienced neuroradiologist. Rarely, there have been reports of people having a
stroke at the time of this procedure but this was related to a catheter of
faulty design which is now no longer used. Bruising, which is common in
Cushing's syndrome, may occur after the catheters are pulled out. Some
people notice flushing of the face after the CRH and rarely it can result in
a fall in blood pressure.
Cushing's Syndrome
You have been diagnosed with Cushing's syndrome (see below) which
results from excessive production of the hormone cortisol, made by the
adrenal glands. In your case, the adrenal glands are being driven by
excessive amounts of another hormone called ACTH. This test is to determine
where that ACTH is coming from. Constant high levels of ACTH are usually
caused by a tumor. Approximately 80% of cases are tumors of the pituitary
gland while the remainder may occur in the lung, pancreas and other sites
(known as "ectopic" sites).
Cushings Syndrome occurs when the body's tissues
are exposed to excessive levels of cortisol for long periods of time. Many
people suffer the symptoms of Cushing's syndrome because they take
glucocorticoid hormones such as prednisone for asthma, rheumatoid arthritis,
lupus or other inflammatory diseases.
Others develop Cushing's syndrome because of overproduction of cortisol by
the body. Normally, the production of cortisol follows a precise chain of
events. First, the hypothalamus, a part of the brain which is about the size
of a small sugar cube, sends corticotropin releasing hormone (CRH) to the
pituitary gland.
CRH causes the pituitary to secrete ACTH (adrenocorticotropin),
a hormone that stimulates the adrenal glands. When the adrenals, which are
located just above the kidneys, receive the ACTH, they respond by releasing
cortisol into the bloodstream.
Cortisol performs vital tasks in the body. It helps maintain blood pressure
and cardiovascular function, reduces the immune system's inflammatory
response, balances the effects of insulin in breaking down sugar for energy,
and regulates the metabolism of proteins, carbohydrates, and fats. One of
cortisol's most important jobs is to help the body respond to stress. For
this reason, women in their last 3 months of pregnancy and highly trained
athletes normally have high levels of the hormone. People suffering from
depression, alcoholism, malnutrition and panic disorders also have increased
cortisol levels.
When the amount of cortisol in the blood is adequate, the hypothalamus and
pituitary release less CRH and ACTH. This ensures that the amount of
cortisol released by the adrenal glands is precisely balanced to meet the
body's daily needs. However, if something goes wrong with the adrenals or
their regulating switches in the pituitary gland or the hypothalamus,
cortisol production can go awry.
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Pituitary Adenoma
Pituitary adenomas cause most cases of Cushing's syndrome. They are
benign, or non-cancerous, tumors
of the pituitary gland which secrete increased amounts of ACTH. Most
patients have a single adenoma. This form of the syndrome, known as
"Cushing's disease," affects women five times more frequently than men.
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Ectopic ACTH Syndrome
Some benign or malignant (cancerous)
tumors that arise outside the pituitary can
produce ACTH. This condition is known as ectopic ACTH syndrome. Lung
tumors cause
over 50 percent of these cases. Men are affected 3 times more frequently
than women. The most common forms of ACTH-producing
tumors are oat cell,
or small cell lung cancer, which accounts for about 25 percent of all lung
cancer cases, and carcinoid tumors.
Other less common types of tumors
that can produce ACTH are thymomas, pancreatic islet cell
tumors, and
medullary carcinomas of the thyroid.
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Adrenal Tumors
Sometimes, an abnormality of the adrenal glands, most often an adrenal
tumor, causes
Cushing's syndrome. The average age of onset is about 40 years. Most of
these cases involve non-cancerous
tumors of adrenal tissue, called adrenal
adenomas, which release excess cortisol into the blood.
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Adrenocortical carcinomas, or adrenal
cancers, are the least common cause of Cushing's syndrome. Cancer
cells secrete excess levels of several adrenal cortical hormones,
including cortisol and adrenal androgens. Adrenocortical carcinomas
usually cause very high hormone levels and rapid development of symptoms.
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Familial Cushing's Syndrome
Most cases of Cushing's syndrome are not inherited. Rarely, however, some
individuals have special causes of Cushing's syndrome due to an inherited
tendency to develop tumors
of one or more endocrine glands.
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In Primary Pigmented Micronodular
Adrenal Disease, children or young adults develop small
cortisol-producing tumors
of the adrenal glands.
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In Multiple Endocrine Neoplasia Type I
(MEN), hormone secreting tumors
of the parathyroid glands, pancreas and pituitary occur. Cushing's
syndrome in MENI may be due to pituitary, ectopic or adrenal
tumors
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