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Tuesday, October 6, 2015
A thyroid nodule is a lump in the thyroid gland that stands out from the rest of the gland. Most thyroid nodules are detected when the doctor feels the thyroid gland as part of a physical examination. Some thyroid nodules are only discovered when the patient has a cat scan of the chest or an ultrasound of the neck.
Most thyroid nodules are not cancers. In fact, only about 5-10% of thyroid nodules are malignant. The rest are fluid filled sacks or cysts, benign tumors that are not cancers, or outgrowths of otherwise basically normal thyroid tissue called colloid nodules. A small percentage of benign thyroid tumors are overactive - making too much thyroid hormone. These tumors are very unlikely to be cancers.
The most important part of the evaluation of a nodule is the doctor's examination. Commonly the doctor will evaluate a nodule using some or all of the following techniques:
When a thyroid nodule is discovered, an ultrasound of the thyroid can help in three ways:
Another test that will be done is called a fine needle aspiration biopsy. If the nodule is large, this may be done by the doctor in the office. If it is small, then it might need to be done by a radiologist under ultrasound guidance.
In this test, the doctor takes a needle, which is actually smaller then the needle used normally for blood drawing, and puts it into the nodule. The skin over the nodule is numbed up so that the doctor can put a needle in several times (up to six). The plunger of the syringe is pulled back several times so that a little tissue juice with some thyroid cells in it is sucked into the barrel of the needle. This material is then pushed out of the needle onto a glass slide and sent to the pathology department. The pathologist looks at the material under the microscope and can tell with very good-not perfect but very good-accuracy whether or not the nodule is suspicious for cancer.
The pathologist's report will come back showing one of five things:
The pathologist may say that there is nothing but blood on the slide. This happens in 10-15% of fine needle aspiration biopsies and is called an "inadequate specimen." If this happens, then the biopsy should be repeated. If it happens twice, consideration should be given to removing the nodule surgically.
The pathologist may say that the nodule appears not to be cancer. This makes it very unlikely, though not impossible, that the nodule is a cancer. In a tiny percentage of cases, the nodule turns out to be a cancer even though the pathologist didn't see anything worrisome on the biopsy. This is called a "false negative biopsy". For this reason, when the biopsy comes back benign, we don't dismiss patients without ever seeing them back again. Instead, we see patients back every six to twelve months for a physical examination of the neck. Thyroid ultrasounds are also periodically repeated. A repeat biopsy is indicated if the nodule is getting bigger (which still doesn't guarantee that it's a cancer, but is suspicious) or if new nodules develop, or abnormal lymph nodes start to grow. As long as nothing changes or the nodule gets smaller by physical examination and ultrasound there is no need for another biopsy. Some endocrinologists believe that every nodule should be biopsied twice over a period of time, because this lowers the false negative rate to an even tinier percentage than a single biopsy does.
The pathologist may see changes in some of the cells that do not definitely indicate cancer, but are not usually seen in biopsies of benign nodules. This finding is referred to as "Atypia of Undetermined Significance" or "Follicular Lesion of Undetermined Significance." When this occurs, the usual practice is to repeat the biopsy.
The pathologist may report that the biopsy is suspicious for cancer. This doesn't absolutely guarantee that there is a cancer in the nodule, because in a small percentage of cases the biopsy is suspicious for cancer but the nodule turns out to be benign (this is referred to as a "false positive rate"). However, the fact that the biopsy is suspicious for cancer means that surgery should be done in order to find out if the nodule is a cancer or not and in order to treat it adequately if it does turn out to be a cancer.
Fifth, the pathologist may say that it's a tumor, but that the biopsy can't tell whether it's a benign tumor or a cancer. In these cases we usually recommend surgery as well because there is about a 20-30% probability of such nodules turning out to be cancers.
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Last Reviewed: Mar 25, 2013
Thomas A Murphy, MD, FACP, FACE
Associate Professor of Medicine
School of Medicine
Case Western Reserve University