Of Benign Thyroidectomies, 9% Carry Papillary Thyroid Microcarcinomas

This study was published in ResearchSquare.com as a preprint and has not yet been peer reviewed.

Key Takeaways

  • The prevalence of papillary thyroid microcarcinoma (PTMc) was 9.3% in 1802 patients who underwent total thyroidectomy for benign disease at a single tertiary center in Spain.

  • The prevalence of PTMc was more than twofold greater among patients with multinodular goiter when compared with patients with other types of underlying disease.

  • The prevalence of PTMc appears to have significantly increased from 2005 to 2020, especially during the final 4 years of this period.

Why This Matters

  • The 9.3% prevalence of PTMc in patients who underwent total thyroidectomy for benign disease was near the lower limit of prevalence rates reported in other studies but was comparable to rates reported for other European cohorts.

  • A possible explanation of the relatively low prevalence rate is that there are no environmental exposures that increase the risk of PTMc in the Navarre region of Spain, where most patients included in the study lived.

Study Design

  • Retrospective, observational study of all 2920 patients who underwent total thyroidectomy for benign disease at the Navarra Hospital Complex in Pamplona, Spain in 2005-2020. 

  • The analysis excluded patients with thyroid carcinomas larger than 1 cm, patients who underwent hemithyroidectomy, and patients with incidental microcarcinomas, which left a study cohort of 1802 patients.

  • Exclusion criteria were strict because the main objective of the study was to focus exclusively on patients with true incidentally discovered PTMc and avoid selection bias.

  • General surgeons with expertise in thyroid pathology performed all thyroidectomies. Expert thyroid pathologists performed routine histological studies on all surgical specimens using a standard protocol.

Key Results

  • Pathology assessments showed that 167 cases (9.3%) had PTMc, classified specifically as occult PTMc.

  • Multinodular goiter was the benign indication for surgery in 88% of patients who had PTMc and for 77% of the patients without PTMc.

  • In a multivariate analysis, patients with multinodular goiter were 2.2-fold more likely to have PTMc than patients with other types of benign thyroid disease, Graves’ disease, or chronic lymphocytic thyroiditis. 

  • The lowest prevalence of PTMc, at 4.9%, was in patients with Graves’ disease.

  • The prevalence of PTMc was twice as great in 2017-2020 compared with the earliest period in 2005-2008. In 2009-2016, prevalence rates were roughly 20% higher than the earliest period, and the differences were not significant.


  • The authors did not identify any study limitations in the preprint.


  • The study received no funding.

  • None of the authors had disclosures.

This is a summary of a preprint research study, “Incidentally Discovered Papillary Thyroid Microcarcinoma in Patients Undergoing Thyroid Surgery for Benign Disease,” by researchers primarily at the Navarra Hospital Complex in Pamplona, Spain, available on Research Square provided to you by Medscape. This study has not yet been peer reviewed. The full text of the study can be found on ResearchSquare.com.

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