Thyroid Nodules (cont.)
How are thyroid nodules diagnosed?
Thyroid nodules usually are discovered by the doctor on a routine physical
examination of the neck. Occasionally, a patient may notice a nodule as a
small lump in their neck when looking in the mirror. Once a nodule is
discovered, a physician will carefully evaluate the nodule.
History. The doctor will need to take a detailed history, evaluating both
past and present medical problems. If the patient is younger than 20 or
older than 70 years of age, there is an increased
likelihood that a nodule is cancerous. Similarly, if there is any history of
radiation
exposure (it was actually a standard treatment to apply radiation to the
head and neck in the 1950's to treat acne!), difficulty swallowing, or a
change
in the voice, the nodule is more likely to be cancerous. Although women tend
to have more thyroid nodules than men, the nodules found in men are more
likely to be cancerous. Despite its value, the history cannot differentiate
benign from malignant nodules. Thus, many patients with risk factors
uncovered in the history will have benign lesions, while others without risk
factors for malignant nodules may still have thyroid cancer.
Physical examination. The physician should determine if there
is one nodule or many nodules, and what the rest of the gland feels like. If
the nodule is fixed to the surrounding tissue (it is not movable), the
probability of cancer is higher. In addition, the physical exam should
include a search
for any abnormal lymph nodes in the nearby area that may suggest the spread
of cancer. In addition to evaluating the area of the thyroid, the physician
should look for any signs of gland malfunction, such as an overproduction or
underproduction of thyroid hormone (hyperthyroidism and hypothyroidism).
Blood tests. Initially, blood tests should be done to assess the function of
the thyroid. These tests include the thyroid hormones, T3 and T4, and the
hormone that stimulates the thyroid gland to produce thyroid hormone, called
thyroid stimulating hormone (TSH). Elevated thyroid hormones and a low TSH
suggest hyperthyroidism. Reduced thyroid hormones and a high TSH suggest
hypothyroidism. A blood test called antithyroid peroxidase antibodies is
useful in diagnosing autoimmune thyroiditis, for example, Hashimoto's
thyroiditis. If surgery is likely to be considered for treatment, it is
strongly recommended that the physician also determine the blood level of
thyroglobulin. Thyroglobulin is a protein for carrying thyroid hormones in
the blood stream, and it is only produced in the thyroid gland. Thus, if a
gland is completely removed, thyroglobulin levels fall. If thyroglobulin
levels start to climb after surgery, there is concern that the cancer may
have recurred, either close to the site where the thyroid was removed or
elsewhere in the body.
Ultrasonography. While evaluating the thyroid gland, a physician may order
an ultrasound examination of the thyroid. The ultrasound examination can:
- Detect nodules that are not easily felt
- Determine the number of nodules and their sizes
- Determine if a nodule is solid or cystic
- Be used to assist in obtaining tissue from the thyroid gland or nodule
with a fine needle
Despite its value, an ultrasound cannot determine whether a nodule is benign
or cancerous.
Radionuclide scanning. Radionuclide scanning with radioactive chemicals is
another imaging technique a physician may use to evaluate a thyroid nodule.
The normal thyroid gland accumulates iodine from the blood and uses it to
make thyroid hormones. Thus, when radioactive iodine (I 123) is administered
orally or intravenously to an individual, it accumulates in the thyroid and causes the gland to "light up" when imaged by
a nuclear camera (a type of Geiger counter). The rate of accumulation gives an
indication of how the thyroid gland and any nodules are functioning. A "hot
spot" appears if a part of the gland or a nodule is producing too much
hormone. Non-functioning or hypo-functioning nodules appear as "cold spots"
on scanning. A cold nodule has a risk of cancer that is higher than a
normally or hyper-functioning nodule. Cancerous nodules are more likely to
be cold because cancer cells are abnormal and don't accumulate the iodine as
well as normal thyroid tissue.
Fine needle aspiration. A
fine needle aspirate (FNA) of a nodule, a type of
biopsy, is the most common direct way to determine what types of cells are
present in the thyroid gland and in nodules. The needle is very small, and
while the procedure is simple and can be done in a doctor's office, anesthetic usually
is injected into the tissues traversed by the needle. Fine needle aspiration is possible if the
nodule is easily felt. If the nodule is more difficult to feel, fine needle
aspiration can be
performed under the guidance of ultrasound. The needle is inserted into the
thyroid gland or the nodule and cells are withdrawn. Usually, several
samples are taken in order to give the best chance of detecting abnormal
cells. The cells are then examined by a pathologist under a microscope. The
value of fine needle aspiration is dependent on the experience of the physician performing the
procedure as well as the pathologist reading the specimen.
Diagnoses that can be made from fine needle aspiration include:
- Benign thyroid tissue (non-cancerous), which can be
consistent with Hashimoto's thyroiditis or a colloid nodule or cyst. This
result is obtained in about 60% of biopsies.
- Cancerous tissue (malignant), consistent with the
diagnosis of papillary, follicular, or medullary cancer. This result is
obtained in about 5% of biopsies. The majority are papillary cancers.
- Suspicious biopsy, showing a follicular adenoma.
Though usually benign, up to 20% of these nodules are found ultimately to be
cancerous.
- Non-diagnostic, usually because not enough cells are obtained. If
repeated, up to 50% of these cases will be able to be diagnosed as benign,
cancerous, or suspicious.
One of the most difficult problems for a pathologist is to be confident that
a follicular adenoma -usually a benign nodule-is not a follicular cell
carcinoma or cancer. In these cases, it is up to the physician and the
patient to weigh the option of surgery on a case-by-case basis, with less
reliance on the pathologist's interpretation of the biopsy. It is also
important to remember that there is a small (3%) risk that a benign nodule
diagnosed by fine needle aspiration may still be cancerous. Thus, even benign nodules should be
followed closely by the patient and physician. Another biopsy may be
necessary, especially if the nodule is growing. While most thyroid cancers
are not very aggressive, that is, they do not spread rapidly, the exception
is poorly differentiated (anaplastic) carcinoma, which spreads rapidly and
is difficult to treat.
Next:
What is the treatment of thyroid nodules? »
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