Thyroid Nodules

What causes thyroid nodules

• Benign overgrowth: colloid nodules and follicular adenomas, often with no clear cause.
• Cysts: fluid-filled nodules, often from degeneration of a solid nodule.
• Iodine deficiency: a major cause of goiter worldwide, uncommon in the US.
• Hashimoto's thyroiditis: chronic inflammation can form nodules.
• Radiation exposure: especially in childhood, increases both nodules and cancer.
• Genetics: family history and syndromes such as multiple endocrine neoplasia type 2 and Cowden syndrome.
• Age and sex: more common with age and in women.

Types of thyroid nodules

Symptoms

Most nodules cause no symptoms and are found by chance on scans of the neck or chest. Possible symptoms include a visible or palpable lump, pressure or difficulty swallowing with large nodules, hoarseness (more concerning for cancer), and symptoms of an over- or underactive thyroid. For help recognizing a lump and deciding what to do, see thyroid lump.

Diagnosis

TSH blood test

The first test. If TSH is low, the nodule may be overactive ("hot"). A radioactive iodine uptake scan confirms this. Hot nodules are rarely cancerous and usually do not need a biopsy. If TSH is normal or high, ultrasound guides the next step.

Ultrasound and TI-RADS

Ultrasound measures the nodule and looks at its composition, echogenicity, shape, margins and bright spots (echogenic foci). The American College of Radiology's TI-RADS gives points for each feature and a category:

Suspicious features include a solid, very dark (hypoechoic) nodule, being taller than wide, irregular margins, microcalcifications and spread beyond the thyroid. The American Thyroid Association uses a similar pattern-based approach.

Fine-needle aspiration (FNA) biopsy

A thin needle is passed into the nodule under ultrasound guidance, usually 2 to 4 passes, in a clinic visit. Local anesthetic is optional. Results use the Bethesda system:

Molecular testing on biopsy samples can help reclassify indeterminate (III and IV) results and avoid unnecessary surgery.

Treatment

Watchful waiting

Most benign nodules need only follow-up ultrasound, often at 12 to 24 months, then at longer intervals if stable. Growth of more than about 20% in two dimensions, or new suspicious features, may prompt repeat biopsy.

Overactive nodules

• Radioactive iodine: shrinks the nodule and stops excess hormone.
• Surgery: removal of the affected lobe.
• Antithyroid medicines: control symptoms short term.

Large benign nodules causing symptoms

• Surgery: lobectomy or total thyroidectomy.
• Radiofrequency or laser ablation: non-surgical options that shrink benign solid nodules, offered at specialist centers.
• Ethanol ablation: for recurrent cysts after drainage.

Cancer

Surgery (lobectomy or total thyroidectomy) is the main treatment, sometimes followed by radioactive iodine and thyroid hormone. Very small, low-risk papillary cancers may be monitored with active surveillance. Most thyroid cancers have an excellent prognosis.

Levothyroxine to shrink benign nodules is no longer recommended for most people, because benefit is small and side effects include bone loss and heart rhythm problems.

Complications

Large nodules and goiters can compress the windpipe or esophagus. Toxic nodules can cause atrial fibrillation and bone loss if untreated. Surgical risks include temporary or permanent hoarseness from nerve injury and low calcium from parathyroid damage, both uncommon with experienced surgeons.

Frequently asked questions

What size thyroid nodule needs a biopsy?

It depends on ultrasound appearance. Under ACR TI-RADS, highly suspicious nodules are biopsied from 1 cm, moderately suspicious from 1.5 cm, and mildly suspicious from 2.5 cm. Benign-looking nodules such as pure cysts and spongiform nodules usually do not need biopsy regardless of size.

What does a Bethesda II result mean?

Bethesda II means the biopsy is benign, with a cancer risk of only a few percent. Most people with a benign result need only periodic ultrasound follow-up. A repeat biopsy may be done if the nodule grows significantly or develops suspicious features.

Can thyroid nodules cause weight gain or fatigue?

Most nodules do not affect thyroid hormone levels, so they do not cause these symptoms. If nodules are part of Hashimoto's thyroiditis with an underactive thyroid, fatigue and weight gain can occur. Overactive nodules cause weight loss, palpitations and anxiety instead.

Do benign thyroid nodules turn into cancer?

Benign nodules very rarely become cancerous. The main reason for follow-up is to catch the small number of cancers that a first biopsy can miss. Stable nodules over several years usually need less frequent monitoring.

Do all thyroid nodules need surgery?

No. Most nodules are benign and only need monitoring. Surgery is recommended for cancer, suspicious biopsy results, some indeterminate results, large nodules causing pressure symptoms, and some overactive nodules. Ablation is an alternative for selected benign nodules.