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 varies with the method of assessment. In middle-aged and older patients, palpation reveals nodules in about 5%. Results of ultrasonography and autopsy studies suggest that nodules are present in about 50% of older adults. Many nodules are found incidentally on thyroid imaging studies done for other disorders.
Most nodules are benign. Benign causes include
- Hyperplastic colloid goiter
- Thyroid cysts
- Thyroid adenomas
Malignant causes include thyroid cancers.
Evaluation of a Thyroid Nodule
Pain suggests thyroiditis or hemorrhage into a cyst. An asymptomatic nodule may be malignant but is usually benign. Symptoms of hyperthyroidism suggest a hyperfunctioning adenoma or thyroiditis, whereas symptoms of hypothyroidism suggest Hashimoto thyroiditis. Risk factors for thyroid cancer include
- History of thyroid irradiation, especially in infancy or childhood
- Age < 20 years
- Male sex
- Family history of thyroid cancer or multiple endocrine neoplasia type 2
- A solitary nodule
- Increasing size (particularly rapid growth or growth while receiving thyroid suppression treatment)
Signs that suggest thyroid cancer include stony, hard consistency or fixation to surrounding structures, cervical lymphadenopathy, and hoarseness due to recurrent laryngeal nerve paralysis.
Initial evaluation of a thyroid nodule consists of testing for
- Thyroid-stimulating hormone (TSH)
- Antithyroid peroxidase antibodies
If thyroid-stimulating hormone (TSH) is suppressed, radioiodine scanning is done. Nodules with increased radionuclide uptake (hot) are seldom malignant. If thyroid function tests do not indicate hyperthyroidism or Hashimoto thyroiditis, fine-needle aspiration biopsy done under ultrasound guidance is done to distinguish benign from malignant nodules. Early use of fine-needle aspiration biopsy is a more economic approach than routine use of radioiodine scans.
Ultrasonography is useful in determining the size of the nodule; fine-needle aspiration biopsy is not routinely indicated for nodules <1 cm on ultrasonography or for nodules that are entirely cystic. Ultrasonography is rarely diagnostic of cancer, although cancer is suggested by certain ultrasonographic or x-ray findings:
- Fine, stippled, psammomatous calcification (papillary thyroid carcinoma)
- Hypoechogenicity, irregular borders, height greater than width on transverse section, irregular macrocalcifications, or rarely dense, homogeneous calcification (medullary thyroid carcinoma)
Treatment of a Thyroid Nodule
- Treatment of underlying disorder
Treatment is directed at the underlying disorder. Thyroxine suppression of TSH to shrink smaller benign nodules is effective in no more than half the cases and is seldom done. Thyroxine is not used to treat cancerous nodules.