Thyroid nodules are common. Studies have shown that 19% – 67% of randomly selected individuals will have thyroid nodules detected by an ultrasound. These nodules are more common in women, the elderly, those with iodine deficiency and those with a history of radiation exposure.
When a patient is diagnosed with a thyroid nodule, it is important to exclude thyroid cancer. Thyroid cancer is not common, but may occur in 5% – 10 % of the patients with thyroid nodules. Risk factors for thyroid cancer include: family history, thyroid cancer syndromes (FMTC, MEN 2A and MEN 2B syndromes), history of head and neck irradiation, an age of younger than 20 or older than 70, sex (male), growing nodules, hard consistency of the nodules, neck lymph nodes and hoarseness.
If a patient is found to have a thyroid nodule after a physical examination, a thyroid function test (measuring of serum TSH level) has to be done first, followed by a thyroid ultrasound -- the most sensitive test to evaluate for thyroid nodules. The next step in diagnostic evaluation of thyroid nodules is a fine needle aspiration (FNA) biopsy of the nodule or nodules. It is the procedure of choice and the most accurate method for evaluating thyroid nodules. Generally, only nodules that are larger than 1 cm should be evaluated because they have greater potential to be clinically significant cancers. Occasionally smaller nodules may be evaluated. They are biopsied if they have suspicious ultrasound characteristics, or if the patient has a history of head and neck irradiation or a positive family history of thyroid cancer.
Performing an FNA biopsy under ultrasound guidance is important because it helps to obtain a sufficient quantity of samples with minimum needle sticks, especially in nodules that are small or partially cystic (complex). In order to improve accuracy of the biopsy, an on-site cytologist can evaluate the biopsy sample for adequacy if a sufficient amount of material can be obtained. This will decrease the rate of non-diagnostic biopsies.
As was mentioned above, the majority of thyroid nodules are benign. Nevertheless, thyroid nodules diagnosed as “benign” require follow-up because of a low but negligible false-negative rate of up to 5% with FNA biopsy. This means that despite a “benign” result, 5% of patients still may have a cancer.
It is recommended that serial thyroid ultrasound examinations be performed when following up on thyroid nodules initially diagnosed as benign by a FNA biopsy. A thyroid ultrasound can detect changes in size, appearance of the nodule and blood flow within the nodule. If an initial thyroid ultrasound detects thyroid nodules, a follow-up ultrasound should be repeated in six months and once a year thereafter -- unless there are some changes within the nodule.
Benign nodules may decrease or slowly increase in size with time. Nodule growth is not itself an indication of malignancy, but growth is an indication for further biopsies. An increase in size of the nodule by 20%, calculated by volume of the nodule (three-dimensional measurements), is considered to be clinically significant. The false-negative rate for benign thyroid nodules on repeated FNA biopsies is low.
Some patients with thyroid nodules may develop symptoms such as difficulty swallowing or breathing, especially with supine position and turning their head to the side of the nodule. Literature supports the usage of surgical approaches for nodules bigger than 4 cm because the incidence of false-negative results is higher. It means that even though the biopsy was benign, the rate of thyroid carcinoma is actually higher than in nodules smaller than 4 cm. Based on this, some surgeons consider performing a diagnostic thyroid lobectomy (removal of one half of the thyroid with the nodule) regardless of an FNA biopsy results (even if it is benign) for thyroid nodules that are greater than or equal to 4 cm.