Index to this Health
Guide
Types of
Thyroid Nodules
Clinical Features
Laboratory Tests
Thyroid Biopsy
Treatment
Prevention of Recurrence
Treatment of Benign Nodules
Irradiation of the Thyroid and Neck Region
Multinodular Goitre
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Health
Guides on Thyroid Disease
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A thyroid "nodule" is a localized swelling
within the thyroid gland. Of most concern is a single swelling, but
sometimes it is part of a "multinodular goitre" in which several such
swellings are present. Multinodular goitre is not uncommon in older
people and often causes no symptoms. Single nodules are also common,
affecting perhaps 5% of the population - although most of those affected
are not aware that there is anything wrong with their thyroid gland.
There are many causes of single nodules in the thyroid gland. Although
cancer is uncommon, it is the most important of these causes since
the main reason to investigate thyroid nodules is to diagnose those
nodules that may be malignant. Cancer is less likely with multinodular
goitres, rather than in single nodules.
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Types
of Thyroid Nodules
The single thyroid nodules is usually
one of four things:
- a fluid-containing cyst;
- a degenerated benign tumour/adenoma;
- a slowly growing adenoma;
- a small percentage is malignant.
Because the rest of the thyroid gland
is usually normal, thyroid function is normal and patients are not
hyper- or hypothyroid.
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Clinical
Features
Thyroid nodules are usually small
and painless. They do not cause any pressure effects in the neck.
Most patients do not even notice the swelling. The swelling is found
by their doctors when they have routine medical checkups or are
examined for other conditions. Thyroid nodules are usually firm,
smooth, and easily felt through the skin if they are large enough
(over 1 cm in diameter). Smaller nodules are only detectable by
ultrasound. The rest of the gland feels normal.
Thyroid cancer usually differs from
benign thyroid nodules. The nodule is often very hard and there
may be associated swellings in the lymph nodes in the neck if the
tumour has spread. However, physical examination alone cannot suffice
to distinguish between benign and malignant nodules.
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One of the most important tests for
nodules is the ultrasound which determines size, shape, and solidity.
Another important test is the radioactive iodine scan which allows
the physician to look at the nodules as well as the surrounding thyroid
gland. If the doctor marks
the outline of the nodule on the overlying skin, at the time the
scan is performed, abnormalities on the scan will correspond to
the position of the nodule. Nodules which do not take up radioactive
iodine are called "cold" nodules. Occasionally, nodules take up
most of the iodine at the expense of the rest of the gland. These
are called "hot" nodules. "Hot" nodules can become overactive and
cause hyperthyroidism. Nodules which take up the same amount of
iodine as the rest of the gland are called "warm" or functioning
nodules. It is only the "cold" nodule that may be malignant - in
fact, only about 10% or less of "cold" nodules are thyroid cancers.
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The next step is
to carry out a fine needle biopsy of the thyroid nodule. Cells
and fluid are removed from the thyroid gland and examined by a
pathologist to determine whether this is benign or malignant.
A needle may also be placed into a thyroid cyst and fluid is drawn
into the syringe. This fluid is usually a reddish-brown colour
because of altered blood on the broken down thyroid tissue within
a benign or malignant tumour, or it is a clear yellow fluid from
a congenital cyst. Very occasionally, pus is drawn off indicating
that the nodule is a thyroid abscess.
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Treatment of thyroid nodules depends
on the nature of the nodule as revealed by these two tests. If the
nodule is "warm" and the biopsy does not show malignant cells, it
can be safely assumed that the nodule is not malignant. However, if
the scan shows a "cold" nodule and the biopsy shows that the cells
are "suggestive of malignancy" then the nodule must be removed. If,
at operation, pathological examination shows the nodule to be malignant,
all abnormal gland is removed. The surgeon also carefully searches
the neck and removes those lymph nodes which may contain malignant
tissue.
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M any physicians put all patients, who
have been operated on for thyroid nodule, on thyroxine for life, in
order to prevent the development of nodules in the remaining tissue.
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Benign thyroid nodules may be treated
with thyroid hormone (e.g. thyroxine) to shut "off" TSH and thereby
hopefully shrink the nodule. Patients treated in this way must be
examined every six months. As long as the nodule does not enlarge,
there is no concern. However, if the nodule enlarges despite treatment
with thyroxine, this would suggest that it may have become malignant
and should be removed . It should also be emphasized that most benign
nodules do not shrink with thyroxine therapy, and fewer
such nodules are treated in this fashion. Cysts never respond to thyroxine.
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In the 1940's and early 1950's, many
children were given X-ray treatment for a variety of benign conditions
of the thymus, adenoids, tonsils, and skin. It was later realized
that this irradiation affected the thyroid gland. In some studies
up to 25% of such people eventually developed thyroid nodules, one
third of whom developed thyroid cancer. Thyroid
nodules which appear following irradiation should be investigated
by clinical examination, thyroid scan, and biopsy just like other
nodules. However if there is a suspicion of malignancy, the thyroid
nodule should be removed and the rest of the gland examined carefully
for the presence of other thyroid cancers. Indeed many clinicians
recommend removal of all single thyroid nodules after irradiation.
What about people who received irradiation
but who do not have a nodule? It is important that such people be
carefully examined by a thyroid specialist because of the high likelihood
of a nodule developing. If no thyroid nodule is seen or felt, there
would be no reason to do a thyroid scan, ultrasound or biopsy and
the patient need only be examined again in six months' time. Only
when a thyroid nodule is found by the doctor should further investigations
be carried out. Such patients may also be given thyroxine therapy,
which may prevent nodule formation under these circumstances.
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When there are many nodules in the thyroid
gland, it is difficult to be certain as to whether or not one of these
nodules is malignant. Luckily, cancer is very rare in association
with multinodular goitre. Thyroxine will only rarely cause multinodular
goitres to shrink, as there are usually areas of either degeneration
or autonomy or both. Indeed thyroxine can bring about hyperthyroidism
in some patients with this disorder. If the goitre is large, or if
it is enlarging over time, surgical removal is appropriate.
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A
printed version of this Health Guide is available to health care
professionals and the public. For more information call the National
Office or contact your local
chapter.
Production of
the printed version of this Health Guide was made possible through
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herein are solely those of the authors and do not necessarily represent
the official policy of Health Canada. |
