Thyroid nodules are scattered lesions caused by abnormal localized growth of thyroid cells. A “nodule” that is palpable but not confirmed on ultrasonography cannot be diagnosed as a thyroid nodule. Nodules that are not palpable on physical examination but are found incidentally on imaging are called “accidental thyroid nodules”.
Thyroid nodules are very common. The detection rate by palpation in the general population is 3-7%, while the detection rate with high-resolution ultrasound can be as high as 20-76%.
76%. In other words, nearly half of the people who have a regular checkup are found to have a thyroid nodule, so it is very common. But what about thyroid nodules or thyroid cancer?
5-15% of thyroid nodules are malignant, i.e. thyroid cancer. The clinical management of benign and malignant thyroid nodules differs, as does the impact on the patient’s quality of life and the medical costs involved. Therefore, the key point in the evaluation of thyroid nodules is the differentiation between benign and malignant. And are there any symptoms of malignant thyroid cancer?
Most patients with thyroid nodules have no clinical symptoms. When combined with abnormal thyroid function, corresponding clinical manifestations may appear. Some patients may experience pressure symptoms such as hoarseness, pressure sensation and difficulty in whistling/swallowing due to nodule compression of surrounding tissues.
The following medical history and physical examination findings are risk factors for thyroid cancer.
1. history of childhood head and neck radiation exposure or exposure to radioactive fallout
2. history of systemic radiation therapy.
3. previous or family history of differentiated thyroid cancer (DTC), medullary thyroid carcinoma (MTC) or multiple endocrine adenomatosis type 2 (MEN2), familial polyposis, certain thyroid cancer syndromes (e.g. Cowden syndrome, Carney syndrome, Werner syndrome, Gardner syndrome, etc.)
4, male.
5, rapid growth of nodules.
6, with persistent hoarseness and dysphonia, and vocal fold pathology (inflammation, polyps, etc.) can be excluded.
7, with dysphagia or whistling difficulties.
8. irregular shape of the nodule and adhesion to the surrounding tissues.
9, with pathological enlargement of the lymph nodes in the neck.
All patients with thyroid nodules should have their serum thyroid stimulating hormone (TSH) levels tested. Studies have shown that patients with thyroid nodules with lower than normal TSH levels have a lower percentage of nodules that are malignant than those with normal or elevated TSH levels.
Thyroglobulin (Tg) is a specific protein produced by the thyroid gland and secreted by the thyroid follicular epithelium. A variety of thyroid disorders can cause elevated serum Tg levels, including DTC, goiter, inflammation or injury to thyroid tissue, and hyperthyroidism (hyperthyroidism), so serum Tg cannot identify benign or malignant thyroid nodules.
Calcitonin (Ct) is secreted by the parafollicular cells (C cells) of the thyroid gland. Serum Ct >100 pg/mL suggests medullary thyroid carcinoma (MTC). However, the incidence of MTC is low, and the specificity of diagnosing MTC is low when serum Ct is elevated but less than 100 ng/mL, so the application of serum Ct indicators to screen for MTC is not recommended or opposed.
High-resolution ultrasonography is the method of choice for the evaluation of thyroid nodules. Neck ultrasound should be performed for palpable suspicion or for “thyroid nodules” suggested by X-ray, computed tomography (CT), magnetic resonance imaging (MRI) or 2-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography (PET). Neck ultrasound can confirm the presence of a “thyroid nodule” and determine the size, number, location, texture (solid or cystic), shape, border, envelope, calcification, blood supply and relationship to surrounding tissues, as well as assess the presence and size, morphology and structural characteristics of lymph nodes in the neck area.
Certain ultrasound signs can help in the differentiation of benign and malignant thyroid nodules. Almost all thyroid nodules with the following two types of ultrasound changes are benign.
1, purely cystic nodules.
2. Nodules with multiple small vesicles occupying more than 50% of the nodule volume and showing spongy changes are 99.7% benign.
The following ultrasound signs suggest a high possibility of thyroid cancer
1. solid hypoechoic nodules.
2, abundant blood supply in the nodule (in case of normal TSH).
3, irregular nodule morphology and margins, halo absence.
4, microcalcifications, pinpoint-like diffuse distribution or clustered distribution of calcifications.
5. concomitant abnormal ultrasound images of cervical lymph nodes, such as rounded lymph nodes, irregular or blurred borders, uneven internal echogenicity, internal calcifications, poorly demarcated dermal medulla, disappearance of lymphatic portals or cystic changes. The ability to identify benign and malignant thyroid nodules by ultrasonography is related to the clinical experience of the ultrasonographer.
Due to the limitations of the resolution of the imaging instrument, thyroid nuclear imaging is suitable for the evaluation of thyroid nodules >1 cm in diameter. In single (or multiple) nodules with decreased serum TSH, thyroid 131I or 99mTc nuclide imaging can determine whether a nodule (or nodules) has autonomic uptake (“hot nodules”). The vast majority of “hot nodules” are benign and usually do not require fine needle aspiration biopsy.
CT and MRI are not superior to ultrasound in assessing the benignity of thyroid nodules. For thyroid nodules to be treated surgically, preoperative CT or MRI of the neck is feasible to show the relationship of the nodule to the surrounding anatomical structures and to look for suspicious lymph nodes to assist in the development of the surgical plan. In order not to interfere with possible postoperative 131I imaging and 131I treatment, the use of iodine-containing contrast agents in CT examinations should be avoided as much as possible.
FNAB may be considered for all thyroid nodules >1 cm in diameter. FNAB is not routinely recommended for thyroid nodules <1 cm in diameter, but ultrasound-guided FNAB may be considered in the presence of
1. ultrasound suggestive of malignant signs in the nodule.
2, with abnormal ultrasound images of the cervical lymph nodes.
3, history of radiation exposure to the neck or exposure to radiation contamination during childhood.
4, history of thyroid cancer or thyroid cancer syndrome or family history.
5. Positive 18F-FDG PET imaging.
6, with abnormally elevated serum Ct levels.
Compared with FNAB under palpation, ultrasound-guided FNAB has a higher success rate of sampling and diagnostic accuracy. To improve the accuracy of FNAB, the following methods can be used: repeated puncture sampling at multiple sites of the same nodule; sampling at sites where ultrasound suggests suspicious signs; sampling at solid sites of cystic nodules with concurrent cyst fluid cytology. In addition, experienced operators and diagnostic cytopathologists are also important to ensure the success rate and diagnostic accuracy of FNAB.