Thyroid nodules are abnormal growths or lumps within the thyroid gland, the butterfly-shaped organ located at the base of the neck. When multiple nodules form, the condition is commonly referred to as a multinodular goiter (MNG). This occurrence is widespread, with ultrasound studies revealing nodules in over half of women aged 50 and older. The vast majority of these growths, often exceeding 90%, are benign and do not represent a serious health concern.
What Causes Multiple Thyroid Nodules?
The development of multiple thyroid nodules results from the thyroid gland’s reaction to chronic stimulation or underlying biological changes. This process often leads to a generalized enlargement of the gland, known as a goiter, with distinct nodules forming within the tissue. Hormonal fluctuations are a significant factor, particularly the long-term effect of mildly elevated Thyroid-Stimulating Hormone (TSH) levels, which prompt thyroid cells to grow and divide.
Historically, the most common global cause was iodine deficiency, as the thyroid requires this mineral to produce hormones. A lack of iodine triggers the pituitary gland to increase TSH secretion, causing the thyroid to enlarge. While modern salt iodization has reduced this factor in many regions, environmental and genetic influences contribute to nodule formation.
Aging also plays a role, with the prevalence of nodules increasing significantly with age. The development of MNG is thought to be an accumulation of growth and repair processes over decades. Chronic autoimmune conditions, such as Hashimoto’s thyroiditis, can also lead to inflammation and tissue changes that promote nodule formation.
Assessing Cancer Risk Through Imaging and Biopsy
The primary goal in evaluating multiple thyroid nodules is to determine if any lesions harbor malignancy. Having a multinodular goiter does not necessarily increase the overall risk of cancer compared to having a single nodule; the risk is assessed on a per-nodule basis. The initial step is a thorough ultrasound examination, which serves as the primary screening tool.
The ultrasound allows endocrinologists to identify specific features suspicious for cancer, guiding the decision for further testing. Highly concerning features include microcalcifications, irregular or spiculated margins, and a “taller-than-wide” shape, indicating growth into surrounding tissue. Nodules that appear darker than the rest of the thyroid tissue (hypoechoic) are considered more suspicious than brighter ones.
Blood tests measure TSH levels to determine if a nodule is “functional,” meaning it is producing thyroid hormone. Nodules that actively produce hormone, resulting in low TSH, are rarely cancerous and typically do not require a biopsy. If suspicious ultrasound features are present, a Fine Needle Aspiration (FNA) biopsy is performed using a thin needle to sample cells for analysis. When multiple nodules are present, the biopsy is reserved for the one with the most concerning ultrasound features, or any nodule exceeding 1.0 centimeter that displays an intermediate or high-risk pattern.
Treatment Strategies and Long-Term Surveillance
For the majority of multiple thyroid nodules found to be benign, the standard approach is active surveillance, also known as watchful waiting. This involves routine follow-up with a physical exam and periodic ultrasound checks, typically performed 12 to 24 months after the initial evaluation. If the nodule remains stable in size and appearance, the surveillance interval may be extended to three to five years.
Treatment with synthetic thyroid hormone, such as levothyroxine, may be considered when TSH levels are mildly elevated, aiming to suppress TSH and potentially slow nodule growth. However, the effectiveness of hormone suppression therapy in shrinking existing benign nodules is variable. This treatment is avoided in older patients or those with heart conditions due to the risk of inducing an overactive thyroid state.
Surgery becomes necessary if the FNA biopsy confirms malignancy or if a large goiter causes compressive symptoms, such as difficulty breathing or swallowing. For non-cancerous but symptomatic goiters, the surgeon may perform a lobectomy, removing only the half of the thyroid gland containing the problematic nodules. A total thyroidectomy, removing the entire gland, is reserved for confirmed cancers or extensive multinodular goiters. For functional nodules producing too much thyroid hormone (toxic multinodular goiter), treatment with radioactive iodine (RAI) is often used to shrink the overactive tissue.