Something I always wondered when I began practice was how radiologists come up with recommended intervals for repeat imaging. Whether this is for a lung nodule, pleural effusion, or thyroid nodule. Lo and behold there are guidelines for when to repeat these diagnostic tests. Today we will be discussing the diagnostic evaluation and treatment of thyroid nodules.


Thyroid nodules are common throughout the population, especially in those who are females. However, there are a number of these nodules in the thyroid gland that go missed due to being nonpalpable on examination. These nonpalpable nodules are often found as incidentalomas on imaging for other reasons.


For these surprise nonpalpable nodules, the same workup should be instituted as the workup for a palpable thyroid nodule felt on examination.


A thyroid nodule can be felt on examination of patients in four to seven percent of cases. They are unintentionally found in up to 40% of patients who undergo ultrasonography of the neck for other causes. Some studies have suggested that up to 76 percent of the general population has at least one thyroid nodule.1


Risk factors for an increasing number and size of thyroid nodules include Graves disease, and pregnancy.1 Low iodine intake is a risk factor for hyperfunctioning nodules.1


Any time that there is a nodule present on the thyroid gland, there is a risk of potential malignancy.In nodules seen on imaging, the risk of malignancy is around 1.5 to 17 percent. However, the true incidence of malignancy cannot be correctly interpreted due to numerous nodules that are too small to be detected on imaging that skews these percentages.1


Risk factors for malignancy include past irradiation to the head and neck, increasing age, history of Graves disease, family history, and history of MEN syndrome.1


Thyroid nodules are often identified by patients when they feel or find a lump in the lower neck area. Other symptoms or chief complaints might include difficulty swallowing, choking sensation, or a cough. Nodules may be multiple or single, tender or nontender, or hard or soft.1


A healthcare provider may find nodules in the thyroid gland on palpation of the area on routine examination. However, nodules that are less than 1cm in size are often difficult to palpation on examation.1


The number one goal when evaluating a thyroid nodule is to determine if it is malignant or not. The first step is to complete a thyroid stimulation hormone (TSH) test and a thyroid ultrasound.




If the TSH is low, then radionuclide scintigraphy with iodine 123 or technetium 99m should be completed to aid in the determination whether a nodule is hyperfunctioning (hot nodule), or if the entire thyroid gland is overactive (toxic multinodular goiter).1


In the past, guidelines recommended a biopsy of smaller lesions, but recent recommendations now state that nodules larger than 1 cm should be biopsied with fine needle aspiration (FNA).If a nodule is less than 1 cm in size, then it can be followed with repeat ultrasonography.1


If more than one nodule is seen on ultrasonography, then multiple nodules should be biopsied. There are no current recommendations on the size when to biopsy multiple nodules or the number to biopsy if there are multiple nodules present.1


Nodules regardless of size should be biopsied if there is the presence of extracapsular invasion or if there is cervical lymphadenopathy noted.1


If the patient has a past medical history of head or neck irradiation, thyroid cancer, or MEN type 2 in a first-degree family member, then biopsies should be taken.1Hyperfunctioning (hot) nodules do not need to be biopsied.


If a nodule is found to be nondiagnostic or indeterminate on FNA, a repeat fine needle aspiration needs to be completed in one to four weeks.


If FNA finds benign results, follow up testing should be completed in six months.If malignant or suspicious for malignancy, then thyroid surgery should be completed.


For hyperfunctioning nodules, radioactive iodine 131 ablation is the first line treatment. Since there is little activity in the surrounding thyroid tissue due to axis suppression, there is minimal uptake of the iodine isotope in the tissue surrounding the nodules; therefore, minimal damage is done to the remaining thyroid gland.


The incidence of thyroid cancer appears to be more common after radioiodine treatment.1 However, these cancers seem to be less aggressive, and overall thyroid cancer mortality is not increased.1


In cases where pathology of FNA is malignant, surgery to remove the affected thyroid lobe or lobes is recommended.1 Diagnostic lobectomy is recommended for nodules 4 cm or larger due to this size being an independent predictor of malignancy. Also, FNA in a nodule this size may miss a malignant area and be falsely read as benign.


Benign nodules should have repeat ultrasonography in six months after the initial FNA that was completed.1 If the nodule has not changed in size, then the interval may be extended to three to five years.1


If the nodule has grown in size, then repeat FNA should be completed with ultrasonographic guidance. If a cystic nodule has recurrent benign FNA results, is can be removed surgically or percutaneously with ethanol injection if they are symptomatic.1


If a solid nodule is benign on repeat FNA, they can be followed with ultrasonography or removed surgically if symptomatic.


There are studies on exogenous levothyroxine suppression in benign nodules which have shown a reduction in the nodule size. However, this treatment is not generally recommended.1


Studies have shown that the rate of thyroid nodules is higher in patients who are pregnant. The workup for these patients should be the same as the general population including ultrasonography and TSH measurement.


In cases of euthyroid or hypothyroid pregnant patients with a nodule, FNA should be completed when indicated.In cases in which the TSH is suppressed, workup should be delayed until after pregnancy and lactation, and then at that point, thyroid scintigraphy can be completed.


If a pregnant patient is symptomatic due to a hyperfunctioning nodule, they should be treated with antithyroid medication, the same as a pregnant patient with hyperthyroidism with Graves disease.


In children, thyroid nodules overall are rare. However, if present, the risk of malignancy is much higher, around 27%.The role of FNA in children has been shown to be not the most useful due to inaccuracy. Some studies note that FNA is as accurate in adolescents as adults, but in children, excision of nodules is recommended instead of FNA for diagnostic purposes.1


In children with a family history of thyroid cancer or MEN type 2 syndrome, preventive thyroidectomy is recommended for treatment of thyroid nodules.1






Resources:


1.Am Fam Physician. Thyroid Nodules. 2013;88(3):193-196. Copyright © 2013 American Academy of Family Physicians.


2.UpToDate. Diagnostic Approach to and Treatment of Thyroid Nodules. Accessed: March 10, 2018.


3.MD Anderson Cancer Center. Thyroid Nodule Evaluation. Accessed: March 10, 2018.


4.Ferri's Clinical Advisor. Thyroid Nodule. 2017.


This article, blog, or podcast should not be used in any legal capacity whatsoever, including but not limited to establishing standard of care in a legal sense or as a basis of expert witness testimony.No guarantee is given regarding the accuracy of any statements or opinions made on the podcast or blog.