Thyroid nodules are benign or malignant growths within the thyroid gland. They are common, increasingly so with increasing age.
(See also Overview of Thyroid Function.)
The reported incidence of thyroid nodules varies with the method of assessment. In middle-aged and older patients, palpation reveals nodules in approximately 5%. Results of ultrasonography and autopsy studies suggest that nodules are present in approximately 50% of older adults (1). Many nodules are found incidentally when head and neck imaging studies are done for other disorders.
General reference
1. Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid 2016;26(1):1-133. doi:10.1089/thy.2015.0020
Etiology of a Thyroid Nodule
Most nodules are benign. Benign causes include
Hyperplastic colloid goiter
Thyroid cysts
Thyroiditis
Thyroid adenomas
Malignant causes include
Evaluation of a Thyroid Nodule
History
Thyroid nodules are mostly asymptomatic, but they can occasionally be painful or cause compressive symptoms in the neck. Pain suggests thyroiditis or hemorrhage into a cyst. An asymptomatic nodule may be malignant but is usually benign. Compressive symptoms, including difficulty swallowing, difficulty breathing, or hoarseness, increase the risk of the nodule being malignant.
Symptoms of hyperthyroidism (ie, palpitations, heat intolerance, weight loss, tremors) suggest a hyperfunctioning adenoma or thyroiditis, whereas symptoms of hypothyroidism (ie, cold intolerance, weight gain, fatigue) suggest Hashimoto thyroiditis.
Risk factors for thyroid cancer include
History of thyroid irradiation, especially in infancy or childhood
Age > 55 years
Female sex (1)
Family history of thyroid cancer or multiple endocrine neoplasia type 2
A solitary nodule or goiter
Dysphonia
Increasing size (particularly rapid growth or growth while receiving thyroid suppression treatment)
Higher thyroid-stimulating hormone (TSH) levels
Although female sex is a risk factor for thyroid cancer, males, particularly older males are more likely to have aggressive disease.
Physical examination
Signs that suggest thyroid cancer include stony, hard consistency or fixation to surrounding structures, cervical lymphadenopathy, and hoarseness (due to recurrent laryngeal nerve paralysis).
Laboratory testing
Initial laboratory evaluation of a thyroid nodule consists of testing for
TSH
If TSH is low (consistent with hyperthyroidism), radioiodine uptake and scanning are done. Nodules with increased radionuclide uptake (hot) are seldom malignant.
If thyroid function tests do not indicate hyperthyroidism, the next step is to examine the nodule with thyroid ultrasonography.
Thyroid imaging
Ultrasonography is useful in determining the size of the nodule and detecting suspicious sonographic characteristics including
Hypoechogenicity
Marked internal vascularity
Irregular borders
Height of the nodule being greater than the width
Irregular macrocalcifications
Fine, stippled psammomatous microcalcifications (papillary thyroid carcinoma)
Dense, homogenous irregular calcification (medullary thyroid carcinoma)
The thyroid imaging and reporting system (TI-RADS) is a risk stratification system for thyroid cancer based largely on ultrasound findings. A TI-RADS classification based on nodule size, echogenicity, composition, shape, margins, and echogenic foci is useful to decide when to proceed with a fine-needle aspiration biopsy (2).
For nodules > 1 cm with suspicious features (TI-RADS 5) or nodules > 1.5 cm with moderately suspicious features (TI-RADS 4), fine-needle aspiration biopsy (FNAB) done under ultrasound guidance is the procedure of choice to distinguish benign from malignant nodules. FNAB is generally not recommended for nodules < 1 cm or for nodules that are entirely cystic.
Fine-needle aspiration biopsy
The Bethesda System for Reporting Thyroid Cytopathology is another useful risk stratification tool. Cytologic examination of the cells obtained from FNAB may distinguish benign (Bethesda II) from suspicious for malignancy (Bethesda V) or malignant (Bethesda VI) lesions. For lesions that are cytologically indeterminate (Bethesda III or IV) (3), molecular analysis of the FNAB aspirate for mutations and rearrangements or measurement of calcitonin for possible medullary thyroid carcinoma may add sufficient diagnostic clarity to allow an optimally informed treatment recommendation.
Evaluation references
1. Lim H, Devesa SS, Sosa JA, Check D, Kitahara CM. Trends in Thyroid Cancer Incidence and Mortality in the United States, 1974-2013. JAMA 2017;317(13):1338-1348. doi:10.1001/jama.2017.2719
2. Tessler FN, Middleton WD, Grant EG, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. J Am Coll Radiol 2017;14(5):587-595. doi:10.1016/j.jacr.2017.01.046
3. Ali SZ, Baloch ZW, Cochand-Priollet B, Schmitt FC, Vielh P, VanderLaan PA. The 2023 Bethesda System for Reporting Thyroid Cytopathology. Thyroid 2023;33(9):1039-1044. doi:10.1089/thy.2023.0141
Treatment of a Thyroid Nodule
Thyroid hormone
Radiofrequency ablation
Thyroidectomy
Radioactive iodine
Treatment of malignant nodules is discussed under Thyroid Cancers.
Treatment is directed at the underlying disorder and depends on cytology results (1).
Benign nodules in patients with Hashimoto thyroiditis or other causes of goiter associated with hypothyroidism may stabilize or shrink with thyroxine replacement in doses that render the patient euthyroid. For small benign nodules (usually ≤ 1.5 cm) not associated with hypothyroidism, thyroxine suppression of TSH effectively shrinks the nodule in no more than half the cases, and is seldom done. Thyroxine is not used to treat cancerous nodules.
Large benign nodules that compress the surrounding neck structures may shrink following radiofrequency ablation.
Partial or complete thyroidectomy is effective for treating nodules that continue to grow or cause compressive symptoms.
Toxic (producing thyroid hormone and causing symptomatic hyperthyroidism) nodules may be treated with radioactive iodine to control hyperthyroidism and reduce nodule size.
Nodules that are not due to thyroid cancer, are not causing compressive symptoms, and are not associated with either hypothyroidism or hyperthyroidism may be safely followed by periodic neck examination and, if there is suspicion of nodule growth, by repeat ultrasound evaluation.
Treatment reference
1. Haugen BR, Alexander EK, Bible KC, et al: 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid 26(1): 1–133, 2016. doi: 10.1089/thy.2015.0020
