Thyroid nodules
are
lumps which commonly arise within an otherwise
normal thyroid gland.
The thyroid is a butterfly-shaped gland located
at the base of your neck, just below your Adam's
apple - about where you'd put a bow tie. Although it
weighs less than an ounce, the thyroid gland
produces hormones that regulate every aspect of your
metabolism, from your heart rate to how quickly you
burn calories.
Sometimes normal thyroid tissue begins to grow,
causing one or more nodules to develop within the
gland. The great majority of these solid or
fluid-filled lumps are noncancerous (benign) and
don't cause any symptoms. In fact, you often won't
know you have a nodule until your doctor discovers
it during a routine medical exam.
Some nodules, however, may become large enough to
press on your windpipe (trachea) or your esophagus,
making it uncomfortable or difficult to swallow. A
few may begin producing excess amounts of thyroid
hormone, leading to
hyperthyroidism, a condition
marked by unintended weight loss, sleep problems and
irritability. And about 5 percent of nodules may be
cancerous (malignant).
Treatment depends on the type of nodule you have.
Small, benign nodules may only require careful
watching, whereas growing or painful nodules may
need to be suppressed with synthetic thyroid
hormone. When tests can't determine whether a nodule
is benign, the nodule may be surgically removed. In
the rare cases when a thyroid nodule is malignant,
the prognosis is often excellent.
Signs and symptoms
Most thyroid nodules don't cause signs or symptoms. Occasionally,
however, some may become so large that you can feel or even see the
swelling at the base of your neck, especially when you're shaving or
putting on makeup. Men sometimes become aware of a nodule because their
shirt collars suddenly feel too tight.
Some nodules produce too much thyroxine, a hormone secreted by your
thyroid gland. The extra thyroxine can cause signs and symptoms such as
sudden, unexplained weight loss, nervousness and a rapid or irregular
heartbeat.
A
thyroid nodule is more likely to be malignant if it:
-
Grows quickly or
feels hard
-
Causes you to be
hoarse or to have trouble swallowing or breathing
-
Causes enlarged
lymph nodes under your jaw or in your neck
Causes
Your thyroid gland consists of two lobes that resemble the wings of a
butterfly. The lobes are separated by a thin section — think of it as
the butterfly's body — called the isthmus. The thyroid takes up iodine
from food you eat and uses it to manufacture two main hormones,
thyroxine (T-4) and triiodothyronine (T-3). These hormones maintain the
rate at which your body uses fats and carbohydrates, help control your
body temperature, influence your heart rate and help regulate the
production of protein. Your thyroid gland also produces calcitonin, a
hormone that regulates the amount of calcium in your blood.
Just why normal thyroid tissue develops into nodules isn't clear. What
is known is that several types of nodules can develop in the thyroid
gland:
-
Colloid nodule.
Most thyroid nodules are colloid nodules — benign overgrowths of
normal thyroid tissue. You may have just one colloid nodule or many.
Although these nodules may grow larger, they don't spread beyond the
thyroid gland.
-
Follicular
adenoma.
This type of nodule also is benign. Unfortunately, doctors can't
distinguish between a benign follicular adenoma and follicular
cancer without surgically removing the nodule. Normally, a
nonsurgical procedure called fine-needle aspiration (FNA) biopsy is
the most sensitive way to determine whether a nodule is benign or
malignant. But FNA biopsy doesn't provide a definitive answer in
cases of follicular adenomas.
-
Thyroid cyst.
These fluid-filled areas of the thyroid can range in size from less
than 1/3 inch to 1 inch or more in diameter. Many thyroid cysts are
entirely filled with fluid, but some cysts, called complex cysts,
also have solid components. Fluid-filled cysts are usually benign,
but complex cysts are sometimes malignant.
-
Inflammatory
nodule.
This occasionally develops as a result of chronic inflammation of
the thyroid gland (thyroiditis). One rare type of thyroiditis —
subacute thyroiditis — causes severe pain in the thyroid gland.
Other types are painless and sometimes occur after pregnancy
(postpartum thyroiditis).
-
Thyroid cancer.
Only about 5 percent of thyroid nodules are cancerous. Although the
chances that a nodule will be malignant are small, you're at higher
risk if you have a family history of thyroid or other endocrine
cancers, are younger than 20 or older than 60, are a man, or have a
history of head or neck radiation. Malignant nodules are usually
large and hard and may cause neck discomfort or pain.
-
Multinodular
goiter.
Goiter is a term used to describe any enlargement of the
thyroid gland. Several factors can lead to a goiter, including the
presence of a number of thyroid nodules. This condition, called
multinodular goiter, can cause a tight feeling in your throat and
difficulty breathing or swallowing.
-
Hyperfunctioning thyroid nodule (toxic adenoma, toxic multinodular
goiter, Plummer's disease).
These nodules grow and produce thyroid hormones independent of the
influence of thyroid-stimulating hormone (TSH), a substance released
by the pituitary gland, which normally regulates the production of
thyroid hormones. Hyperfunctioning thyroid nodules cause high blood
levels of thyroxine and low or non-existent levels of TSH. A genetic
defect of the TSH receptors may play a role in the overactivity of
these nodules.
Risk factors
Although the exact cause of most thyroid nodules isn't known, certain
factors appear to increase your risk:
-
Heredity.
If a parent or sibling has thyroid nodules, you have a greater
chance of developing them as well.
-
Age.
Because the likelihood of developing thyroid nodules increases as
you grow older, some changes in thyroid tissue may occur as a normal
part of aging.
-
Sex.
Women are more likely to develop thyroid nodules than men are.
-
Radiation
exposure.
In the 1940s and 1950s, children, teenagers and even newborns were
often treated with radiation for benign conditions such as acne or
enlarged tonsils. If you once had radiation therapy to your neck or
head for conditions such as acne, you have an increased risk of
developing thyroid nodules.
-
You're also at
increased risk if you were exposed to radioactive particles released
into the air during atomic weapons testing or in nuclear power plant
accidents, such as the 1986 Chernobyl disaster in the former Soviet
Union. Radiation not only affects people, animals and crops in the
immediate vicinity of the release but also can affect areas
thousands of miles away.
-
Certain thyroid
conditions.
Nodules are more likely to form in people who have or have had
thyroiditis — a chronic inflammation of the thyroid gland.
When to seek medical advice
See your doctor if you notice any unusual swelling in the lower front of
your neck, if you have trouble breathing or swallowing, or if you feel
as if you have a lump in your throat. Also seek medical care if you
develop signs and symptoms of hyperthyroidism, such as sudden weight
loss even though your appetite is normal or has increased, a pounding
heart, trouble sleeping, muscle weakness, and nervousness or
irritability. It's important to completely describe the changes you've
observed, because many signs and symptoms of hyperthyroidism may be
associated with a number of other conditions.
Thyroid nodules
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