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Thyroid nodule: definition, causes and frequency

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Thyroid nodule: definition, causes and frequency

Understand what a thyroid nodule is, why it forms, how to assess whether it is benign or malignant, and when to consider treatment · Cochin AP-HP · Pr Anthony Dohan · Updated April 2026

Quick answer

A thyroid nodule is an area of the thyroid gland whose structure differs from normal tissue: adenoma, cyst or, more rarely, carcinoma. Very common (up to 50-70% of the adult population), they are most often benign and discovered incidentally on ultrasound.

What is a thyroid nodule?

A thyroid nodule is an area of the thyroid gland whose structure differs from normal thyroid tissue. It may be a proliferation of thyroid cells (adenoma), a cyst (fluid collection), or, more rarely, a carcinoma. Thyroid nodules are very common: they are detected in about 50 to 60% of adults on systematic ultrasound.

The vast majority of thyroid nodules (95%) are benign. Only about 5% prove to be malignant, with an excellent prognosis for most (papillary cancer with > 95% 10-year survival).

Types of thyroid nodules

  • Solid nodule: made up entirely of proliferating thyroid cells. May be benign (adenoma) or malignant.
  • Thyroid cyst: pure fluid collection, almost always benign.
  • Mixed nodule (solid and cystic): the most frequent. The solid component is assessed by ultrasound and the TIRADS score.
  • Toxic nodule: hyperfunctioning, secreting excess hormones (hyperthyroidism).
Ultrasound featureFavours benignSuspicious for malignancy
MarginsRegular, well definedIrregular, poorly defined
EchogenicityIso- or hyperechoicHypoechoic
CalcificationsCoarse, peripheral"Salt-grain" microcalcifications
VascularisationPeripheralCentral, chaotic
ShapeWider than tallTaller than wide
TIRADS score
The TIRADS score (Thyroid Imaging Reporting and Data System) classifies nodules from TIRADS 1 (no nodule) to TIRADS 5 (highly suspicious). It guides the indication for fine-needle aspiration. A TIRADS 3 nodule < 15 mm can be monitored. A TIRADS 4 or 5 nodule should undergo fine-needle aspiration.

Frequently asked questions

Is a thyroid nodule often cancer?
No. 95% of thyroid nodules are benign. The prevalence of thyroid cancer is about 5% of nodules discovered, and the vast majority are papillary cancers with a good prognosis (> 95% 10-year survival).
Do all thyroid nodules need surgery?
No. The vast majority of benign nodules do not require surgery. Surgery is indicated in cases of confirmed malignancy, compression (dysphagia, dysphonia), refractory hyperthyroidism, or a large nodule causing significant discomfort. Thyroid radiofrequency is a minimally invasive alternative to surgery for symptomatic benign nodules.
How can I tell whether a nodule is benign?
Ultrasound with the TIRADS score and fine-needle aspiration (analysis of cells under the microscope) make it possible to distinguish benign from malignant nodules in the vast majority of cases. Fine-needle aspiration is recommended for TIRADS 4 or 5 nodules, or for TIRADS 3 nodules > 2-3 cm.
Learn more
Radiofrequency ablation of thyroid nodules at Cochin

Minimally invasive technique for ablation of benign thyroid nodules by radiofrequency.

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On the same topic

Scientific references

Indications et contre-indications de la thermoablation des nodules thyroïdiens bénins (Indications and contraindications of thermal ablation of benign thyroid nodules)

Muller A, Villard N, Papadopoulos P, on behalf of the thyroid and ultrasound working group of the CERF, the SFR and the CIREOL (including Dohan A). J Imagerie Diagn Interv 2026. French national consensus.

2020 European Thyroid Association clinical practice guideline for the use of image-guided ablation in benign thyroid nodules

Papini E, Monpeyssen H, Frasoldati A, Hegedüs L. Eur Thyroid J 2020;9:172-185.

2017 Thyroid Radiofrequency Ablation Guideline: Korean Society of Thyroid Radiology

Kim JH, Baek JH, Lim HK, et al. Korean J Radiol 2018;19(4):632-655.

Why this page is trustworthy

Written by the Interventional Radiology team at Cochin Hospital AP-HP, Université Paris Cité. Medically reviewed by an interventional radiologist of the department. Last updated: July 2026.

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