The thyroid gland is located at the front of the neck, just in front of the windpipe. It secretes thyroid hormones, which regulate the function of nearly every organ system in the body, from the nervous system to the digestive system. This type of gland is called an endocrine gland. The medical specialty that deals with diseases of these glands is called endocrinology, while the surgical specialty is known as endocrine surgery. Enlargement of the thyroid gland is called goiter. In the 1960s, patients with very large neck swellings due to goiter were common, but today such cases are rare. Instead, thyroid nodules, often detected incidentally during a routine check-up by ultrasound or physical examination, have become the most common thyroid disorder. Hormonal disorders of the thyroid are also frequently encountered.

When the thyroid gland produces excessive amounts of hormones, a condition known as hyperthyroidism, younger patients often experience weight loss despite an increased appetite. Older patients may develop heart palpitations, hand tremors, excessive sweating, heat intolerance, irritability, menstrual irregularities in women, thinning and hair loss, and diarrhea. Hypothyroidism, which is more common and results from insufficient hormone production, may cause swelling of the body and especially the face, fluid retention, weight gain, constipation, menstrual irregularities, coarse hair with hair loss, dry skin, cold intolerance, slowed movements, and in advanced cases, impaired mental function.

Thyroid nodules of varying sizes are found in approximately 40% of the general population and up to 60% of women. Around 95% of these nodules are benign, while approximately 5% contain thyroid cancer. Hypothyroidism, which is more common than hyperthyroidism, has become increasingly prevalent due to the rapid rise in thyroid inflammation in recent years, affecting up to 20% of women around the age of 40.

Since the year 2000, the introduction of iodized salt has been an important public health measure to protect future generations from goiter. However, as observed in other countries that implemented similar programs, such as Argentina and Switzerland, the following two decades saw a four- to fivefold increase in thyroid inflammation (thyroiditis), particularly Hashimoto's thyroiditis, as well as thyroid cancer developing on this background. A similar trend has been observed in our country. Therefore, iodized salt is recommended for infants and growing children, whereas adults—especially those with thyroid disease—are generally advised to use non-iodized salt. Ideally, meals should be prepared without salt, and two types of salt should be available at the table: iodized salt for children and non-iodized salt for adults.

Every routine health check-up should include measurement of TSH, the most sensitive indicator of thyroid function, as well as a thyroid ultrasound examination. In addition, just as mammography is used for breast cancer screening and Pap smear testing for cervical cancer, thyroid ultrasound and fine-needle aspiration biopsy should also be included in public health screening programs.

In the past, thyroid hormone tests and thyroid scintigraphy were the primary diagnostic methods. Today, scintigraphy is mainly used to determine whether the thyroid gland is overactive or underactive, while ultrasound is preferred for evaluating thyroid nodules and detecting thyroid cancer because of its greater accuracy.