Thyroid nodules are extremely common. The American Thyroid Association notes that by age 60 roughly half of all people have a nodule detectable by examination or imaging, and that over 90 percent of such nodules are benign. What determines whether a nodule needs a biopsy is its appearance on ultrasound combined with its size, and the fact that most are found by accident on a scan done for something else.

The first two tests

The 2015 American Thyroid Association nodule guideline recommends that serum TSH be measured during the initial evaluation of a patient with a thyroid nodule, and that thyroid ultrasound with a survey of the cervical lymph nodes be performed in all patients with known or suspected nodules. If the TSH is low, a radionuclide scan comes next, because a nodule that is making excess hormone is almost never cancer and is managed as hyperthyroidism instead. If TSH is normal or high, a scan is not needed and ultrasound features decide.

What the ultrasound features mean

High suspicion nodules are solid and hypoechoic with at least one of irregular margins, microcalcifications, a taller than wide shape, or rim calcification with extrusive soft tissue. That pattern carries an estimated malignancy risk above 70 percent. Spongiform nodules and purely cystic nodules sit at the other end, with estimated risk under 3 percent and under 1 percent respectively. Those categories are what set the biopsy threshold.

Ultrasound pattern	Estimated malignancy risk	Fine needle aspiration at
High suspicion	More than 70 to 90 percent	1 cm or larger
Intermediate suspicion	10 to 20 percent	1 cm or larger
Low suspicion	5 to 10 percent	1.5 cm or larger
Very low suspicion, including spongiform	Under 3 percent	Consider at 2 cm; observation also reasonable
Benign, purely cystic	Under 1 percent	No biopsy needed

After a benign biopsy

About 80 percent of fine needle aspirations return benign. The American Thyroid Association describes follow-up with ultrasound every 6 to 12 months and annual physical examination, with surgery considered if a nodule keeps growing or develops worrying features. Note that the 2025 American Thyroid Association guideline covers differentiated thyroid cancer and explicitly defers nodule evaluation to the separate nodule guideline, so the 2015 thresholds above remain the current reference.

Ask for a copy of your ultrasound report with the described pattern and the exact measurements in three dimensions, since growth is judged against those numbers. If a biopsy is recommended, ask which of the five patterns your nodule fits, because that single word determines everything that follows.

Fine needle aspiration results are reported using the Bethesda system. Category II is benign, categories III and IV are indeterminate, and categories V and VI indicate suspicious for or consistent with malignancy. Molecular testing is used to refine risk in Bethesda III and IV nodules and can reduce diagnostic surgery.

Significant growth on surveillance is usually defined as a 20 percent increase in at least two dimensions with a minimum increase of 2 mm, or a 50 percent increase in volume. Features that raise concern independent of size include new cervical lymphadenopathy, extrathyroidal extension and vocal cord paralysis. A suppressed TSH shifts the pathway: obtain a radionuclide uptake scan, since autonomously functioning nodules rarely require cytology. Routine thyroid ultrasound screening in asymptomatic people with a normal examination is not recommended and drives overdiagnosis.

I have a thyroid nodule. When is that a concern?

The first two tests

What the ultrasound features mean

After a benign biopsy

Sources

The first two tests

What the ultrasound features mean

After a benign biopsy

Sources

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