The Thyroid Gland
The thyroid gland is a small butterfly-shaped gland located in the front of the neck. It is divided into two lobes, connected by a narrow strip of thyroid tissue known as the isthmus. Structurally, the thyroid gland is organized in small follicles that store the thyroid hormones.
Functionally, the thyroid gland is going to produce three hormones, triiodothyronine (T3), tetraiodothyronine (T4), and calcitonin. T3 and T4 play a crucial role in controlling our metabolism and they are also important for growth and brain development during childhood. On the other hand, calcitonin is involved in regulating calcium and bone metabolism.
Iodine is a vital component in thyroid hormone synthesis. Interestingly, we are not able to make this element, so we rely on our nutrition to get all the iodine we require in order to achieve normal thyroid function.
Thyroid nodules are abnormal growths or lumps that originate in the thyroid gland. They can be classified according to the content inside the nodule as solid, predominantly solid, cystic (filled with fluid), and, predominantly cystic.
This condition is fairly common. Up to 5 to 10% of the population in the US may develop a palpable nodule in their lifetime. Additionally, thanks to the use of high-resolution ultrasounds, it has been found that 19 to 68% of randomly selected individuals have thyroid nodules.1
Most thyroid nodules are benign and asymptomatic (only 7 to 15% are malignant).1 However, they may cause symptoms like difficulty swallowing, pain, and/or tenderness. Additionally, depending on their size, they can become a cosmetic concern.
Solitary thyroid nodules are associated with a higher incidence of malignancies compared to multinodular disease, especially in children. However, they are not that common (less than 2% in children and 4% in adults).2
Additionally, depending on whether the nodule is actively secreting thyroid hormones or not, it can be classified as a toxic nodule. Hyperfunctioning nodule(s) can cause the enlargement of the gland (goiter) and a condition known as hyperthyroidism (overactive thyroid). If a single autonomous nodule is involved in this process, it is known as a toxic thyroid nodule or a toxic adenoma. On the other hand, if more than one nodule is involved it is called a toxic multinodular goiter.
Thyroid nodules are usually asymptomatic. However, some of the symptoms associated with thyroid nodules may include:
- Difficulty swallowing
- Persistent cough
- Shortness of breath
- Foreign body sensation in the neck
Additionally, toxic nodules may cause symptoms associated with excess thyroid hormone release. Common symptoms seen in patients with hyperfunctioning thyroid nodules may include:
- Unexplained weight loss
Palpable thyroid nodules are usually found during a physical examination. Following the diagnosis of a thyroid nodule, the next step is to assess thyroid function and to determine the underlying condition.
The initial laboratory assessment of a thyroid nodule includes the measurement of thyroid-stimulating hormone (TSH), T3, and T4. These results will determine if the thyroid gland is functioning properly or if there is an issue like hyperthyroidism or hypothyroidism. Most patients with a solitary thyroid nodule have normal levels of TSH.1
Serum antithyroid peroxidase (anti-TPO) antibody and antithyroglobulin (anti-Tg) antibody levels are important diagnostic tools if the patient has relevant history suggesting the possibility of an autoimmune disorder like Hashimoto thyroiditis.1
An ultrasound is a very cost-effective way of determining the size, characteristics (solid or cystic), and the number of thyroid nodules. Additionally, the use of high-resolution sonography combined with Doppler can give more relevant information to help diagnose the condition. However, ultrasonography is not reliable enough to determine if a nodule is malignant or not.1
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Fine-Needle Aspiration Biopsy (FNAB)
FNAB is currently the most important diagnostic tool for thyroid nodules. Using a very fine needle, a doctor can gather a sample of thyroid tissue to diagnose the underlying condition. This procedure is usually quite simple and can be performed in a doctor’s office with local anesthesia.
The results of the FNAB can be divided into:
- Benign: the lesion has less than a 1% chance of being malignant.
- Atypia: the lesion has a 5 to 10% chance of being malignant.
- Follicular neoplasm: the lesion has a 20 to 30% chance of being malignant.
- Suspicious for malignancy: the lesion has a 50 to 75% chance of being malignant.
- Malignant: the lesion has a 100% chance of being malignant.
- Nondiagnostic: not enough cells were gathered, therefore a diagnosis cannot be obtained.
The use of ultrasound-guided FNAB yields better results and decreases the chance of having a nondiagnostic result, even on cystic or predominantly cystic nodules.1
This is a nuclear imaging study that uses radioactive isotopes to assess thyroid function. Nuclear imaging of the thyroid can be used to establish if a nodule is hot (hyperfunctioning), warm (normal), or cold (hypofunctioning).
This procedure is no longer a first-line option due to its high cost and the fact that there are better diagnostic tools available.
Benign asymptomatic thyroid nodules can be monitored regularly and do not require surgery. Monitoring usually involves regular visits to a doctor and ultrasounds to assess any changes in the size of the nodules.
Thyroidectomy is the removal of the thyroid gland or lobe, and is indicated for malignant thyroid nodules.3
Patients with follicular neoplasms have a 20 to 30% chance of having thyroid cancer. Therefore, they usually undergo a lobectomy to remove the affected thyroid lobe. After analyzing the removed tissue, if it turns out to be malignant, a completion thyroidectomy is performed to remove the remaining thyroid tissue.3
Patients with a thyroid nodule causing hyperthyroidism, that can’t or refuse to be treated with radioactive iodine therapy or a medical approach can be treated with surgery.3
Symptomatic benign thyroid nodules may also be surgically removed.3
Radioactive Iodine Therapy
Administering radioactive iodine for the thyroid gland to absorb causes targeted damage to the tissue. As a result, toxic nodules decrease in size and the signs and symptoms of hyperthyroidism can subside (usually within 2-3 months).
Radioactive iodine therapy is the most widely used treatment for toxic nodules in the United States.4
A single dose of this therapy has been shown to reduce goiter size by up to 40% and it usually succeeds in 85-100% of patients with toxic nodular goiter.5
Some drugs like Methimazole and Propylthiouracil can be used to stabilize patients with a hot (hyperfunctioning) thyroid nodule before surgery. Additionally, Propylthiouracil is used in pregnant patients with thyrotoxicosis.
These medications can also be used as long-term alternatives for patients with toxic thyroid nodules that refuse or are not candidates for surgery or radioactive iodine therapy.
Thyroid Radiofrequency Ablation (RFA)
Radiofrequency ablation (RFA) is commonly used in patients with benign solid or predominantly solid thyroid nodules (proven by a Fine-needle Aspiration Biopsy or a Core-needle Biopsy) that cause symptoms or have become a cosmetic issue due to their size.6
Radiofrequency ablation has also been used to treat nodules that are actively functioning (Autonomously Functioning Thyroid Nodules). However, the evidence behind this indication is still not strong enough.6
The management of recurrent thyroid cancer is another viable indication for radiofrequency ablation (RFA). Additionally, RFA is proving to be a good alternative to surgery in patients with primary thyroid cancer that either refuse surgery or are not able to tolerate it.6
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1.) Steven K Dankle, M. D. (2021, July 15). Thyroid nodule: Background, clinical outline, diagnostic workup. https://emedicine.medscape.com/article/127491-overview#a1
2.) Andre Hebra, M. D. (2021, June 14). Solitary thyroid nodule. Practice Essentials, Background, Pathophysiology. https://emedicine.medscape.com/article/924550-overview#showall
3.) Neerav Goyal, M. D. (2021). Thyroidectomy. Overview, Preparation, Technique. https://emedicine.medscape.com/article/1891109-overview#a1
4.) Kravets, I. (2016, March 1). Hyperthyroidism: Diagnosis and treatment. American Family Physician. https://www.aafp.org/afp/2016/0301/p363.html#afp20160301p363-b2
5.) Philip R Orlander, M. D. (2021, June 14). Toxic nodular goiter. https://emedicine.medscape.com/article/120497-overview#a4
6.) Kim, J.-hoon, Baek, J. H., Lim, H. K., Ahn, H. S., Baek, S. M., Choi, Y. J., Choi, Y. J., Chung, S. R., Ha, E. J., Hahn, S. Y., Jung, S. L., Kim, D. S., Kim, S. J., Kim, Y. K., Lee, C. Y., Lee, J. H., Lee, K. H., Lee, Y. H., Park, J. S. Guideline Committee for the Korean Society of Thyroid Radiology (KSThR) and Korean Society of Radiology. 2017 thyroid radiofrequency ablation guideline: Korean Society of Thyroid Radiology. https://doi.org/10.3348/kjr.2018.19.4.632
The above information explains what is involved and the possible risks. It is not meant to be a substitute for informed discussion between you and your doctor, but can act as a starting point for such a discussion.