7.3 Thyroid Nodules and Cysts

10.1055/b-0038-162778

7.3 Thyroid Nodules and Cysts

Key Features

A thyroid nodule is a discrete lesion within the thyroid gland that is radiologically distinct from the surrounding thyroid parenchyma.
Nodular disease of the thyroid gland is estimated to be present in 5 to 10% of the population.
Thyroid nodules are more common in women.
Less than 5% of thyroid nodules are malignant.

The prevalence of thyroid nodules is 2 to 6% by palpation, 19 to 35% with ultrasound, and 8 to 65% in autopsy data. The important question when a thyroid nodule is detected is whether the nodule is in fact malignant.

Epidemiology of Nodules

Females are affected more than males. Nodule incidence increases with age and is increased in people with iodine deficiency and after radiation exposure. The prevalence of cancer is in thyroid nodules is higher in children, adults < 30 years or > 60 years old, patients with a history of head and neck radiation, and those with a family history of thyroid cancer. The prevalence of cancer may be lower in patients with multinodular goiters and autonomously hyperfunctioning (“hot”) nodules.

Clinical

The usual presentations of thyroid nodules are as a lump in the neck noted by the patient, as an incidental finding during routine physical examination, or during a radiologic procedure such as carotid ultrasonography or neck computed tomography (CT). Symptoms associated with increased risk of malignancy include a rapid increase in size, dysphagia, hoarseness (nerve involvement), and pain.

Evaluation of Nodules

History

Pertinent history includes prior head and neck irradiation, thyroid carcinoma in a first-degree relative, rapid growth of the nodule, hoarseness, dysphagia, neck pain or pressure, and any symptoms of hyperthyroidism (e.g., due to an autonomous hot nodule) or hypothyroidism (e.g., due to Hashimoto′s thyroiditis). Family history of pheochromocytoma, hyperparathyroidism, chronic constipation and diarrhea, hypertension may be indicative of a multiple endocrine neoplasia (MEN) syndrome.

Physical Exam

A complete physical exam focusing on the thyroid gland and adjacent cervical lymph nodes should be performed. The nodule should be palpated to note size, consistency, mobility, and tenderness. Vocal fold mobility (nasopharyngoscope) should be noted. Cancer may be suspected when nodules are > 4 cm in size, when they are fixed to the surrounding structures, or when there is associated lymphadenopathy or vocal fold paralysis.

Labs

Thyroid function tests should be obtained as part of the initial evaluation of a solitary thyroid nodule. Serum thyroglobulin (Tg) levels are not indicated in the evaluation of solitary thyroid nodule.

Imaging

Nuclear imaging cannot reliably distinguish between benign and malignant nodules and is not required if nodules are present. However, in patients with a suppressed thyroid-stimulating hormone (TSH) level, a thyroid scan determines regional uptake or function and can be used as a secondary study.
Diagnostic thyroid/neck ultrasound should be performed in all patients with a suspected thyroid nodule, nodular goiter, or radiographic abnormality suggesting a thyroid nodule incidentally detected on another imaging study.
Diagnostic thyroid ultrasound will help to determine whether there is truly a thyroid nodule that corresponds to the palpable abnormality or a thyroid cyst; to look for other nonpalpable thyroid nodules that may also need to be biopsied and the location and the number of the nodules; and to guide fine-needle aspiration biopsy (FNAB) ( Table 7.4; Table 7.5; Table 7.6 ).
Thyroid sonography with survey of the cervical lymph nodes should be performed in all patients with known or suspected thyroid nodules.
If serum TSH is low, a radionuclide thyroid scan may be used determine whether a nodule is “hot,” “warm,” or “cold”; a hot functioning nodule rarely harbors malignancy. Radionuclide scanning alone is not the most accurate technique to distinguish benign from malignant thyroid disorders.
CT and magnetic resonance imaging (MRI) are used to evaluate adenopathy, multinodular goiters causing pressure symptoms, substernal goiter, airway and vascular displacement, and invasion of tumor. These studies, however, are not routinely employed.
Consider a chest CT to evaluate displacement of trachea seen on plain chest radiograph.
Focal ¹⁸F-fludeoxyglucose (FDG)–positron emission tomography (PET) uptake within a sonographically confirmed thyroid nodule conveys an increased risk of thyroid cancer, and FNAB is recommended for those nodules > 1 cm.

**Table 7.4** Ultrasound patterns of thyroid nodule and malignancy
High suspicion [malignancy risk 70–90%]:
Solid hypoechoic nodule or solid hypoechoic component of a partially cystic nodule with one or more of the following features: irregular margins, microcalcifications, taller than wide shape
Intermediate suspicion [malignancy risk 10–20%]:
Hypoechoic solid nodule without high-suspicion features
Low suspicion [malignancy risk 5–10%]:
Isoechoic or hyperechoic solid nodule, or partially (> 50%) cystic nodule, with eccentric solid area without high-suspicion features
Very low suspicion [< 3%]:
Spongiform or partially cystic nodules without high- or intermediate-suspicion features
Benign [< 1%]: Purely cystic nodules

**Table 7.5** Sonographic features of thyroid nodule that warrant biopsy
	Threshold for FNAB
Solid nodule
With suspicious sonographic features	≥ 1.0 cm
Without suspicious sonographic features	≤ 1.5 cm
Mixed cystic–solid nodule
With suspicious sonographic features	≥ 1.5–2.0 cm
Without suspicious sonographic features	≤ 2.0 cm
Spongiform nodule	≥ 2.0 cm
Simple cyst	Not indicated
Suspicious cervical lymph node	FNAB node ± FNAB associated thyroid nodule(s)

**Table 7.6** Bethesda Diagnostic Categories for thyroid cysts and nodules
Bethesda Diagnostic Category			Risk of malignancy	Usual management
I	Nondiagnostic or unsatisfactory	Cyst fluid only Virtually acellular specimen Other (obscuring blood, clotting artifact, etc.)	1 to 4%	Repeat FNAB with ultrasound guidance
II	Benign	Consistent with a benign follicular nodule (includes adenomatoid nodule, colloid nodule, etc.) Consistent with lymphocytic (Hashimoto′s) thyroiditis in the proper clinical context Consistent with granulomatous (subacute) thyroiditis Other	0 to 3%	Clinical follow-up
III	Atypia of undetermined significance or follicular lesion of undetermined significance		5 to 15%	Repeat FNAB Molecular testing
IV	Follicular neoplasm of suspicious for a follicular neoplasm	Specify if Hurthle cell (oncocytic) type	15 to 30%	Molecular testing Surgical lobectomy
V	Suspicious for malignancy	Suspicious for papillary carcinoma Suspicious for medullary carcinoma Suspicious for metastatic carcinoma Suspicious for lymphoma Other	60 to 75%	Molecular testing Surgical lobectomy or Near-total thyroidectomy
VI	Malignant	Papillary thyroid carcinoma Poorly differentiated carcinoma Medullary thyroid carcinoma Undifferentiated (anaplastic) carcinoma Squamous cell carcinoma Carcinoma with mixed features (specify) Metastatic carcinoma	97 to 99%	Near-total thyroidectomy

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7.3 Thyroid Nodules and Cysts