A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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Abbreviations & Definitions

FNAB fine-needle aspiration biopsy

What is the study about? The likelihood of a radiation-induced thyroid nodule being malignant depends neither on its size nor number and biopsying only the largest nodule can miss up to half the thyroid cancers

The full article title: “Size, number, and distribution of thyroid nodules and the risk of malignancy in radiation-exposed patients who underwent surgery.” It is in the April 2008 Issue of the Journal of Clinical Endocrinology and Metabolism (volume 93, Issue 6, pages 2118-2193). The authors are DV Mihailescu and AB Schneider.

To view the abstract of this article see:

What is known about the problem being studied? There are few studies to guide the selection of nodules for FNAB in patients exposed to radiation as children and young adults.

What was the aim of the study? To evaluate how thyroid nodule size and number influence the risk of malignancy in patients exposed to radiation as children.

Who was studied? To study the relationship between malignancy and nodule size, only nodules of known size were included, leaving 1998 nodules, 399 of which were malignant, in 1059 patients who had been exposed to irradiation before the age of 16 years for benign conditions of the head and neck and subsequently had surgery for thyroid nodules.

How was the study done? The size, location and diagnosis of malignant nodules were determined from the pathology report. The rank order of the largest malignant nodule compared with the rest of the patient’s nodules was used to calculate how many cancers would have been missed if the nodule size were the only factor used to determine the need for FNAB.

What were the results of the study? There was no increase in the risk of malignancy with increasing nodule size and the risk of malignancy in a nodule was similar with solitary (19%) and multiple (17%) nodules. Still, thyroid cancer was found in fewer patients (19%) with solitary nodules than patients with multiple nodules (31%). Performing FNAB on only the largest nodules would have missed 42% of the 264 thyroid cancers. If only the two largest nodules had been biopsied, 45 cases of thyroid cancer (17%) would have been missed.

How does this compare with other studies? Although the risk of malignancy in nodules of non-irradiated patients is generally greater with larger nodules, some studies suggest this is different in irradiated patients. This study is in accord with the American Thyroid Association guidelines on thyroid cancer and nodules that is available at no cost at the following website:

What are the Limitations of this study? Before 1993 surgery was performed on the basis of physical examination that disclosed thyroid nodular disease. Also, the size and location of thyroid nodules was not available on all patients.

What are the implications of this study? This study has five major findings:

  • The likelihood of a radiation-induced nodule being malignant depends neither on its size nor presence of other thyroid nodules.
  • The risk for thyroid cancer increases when a radiation-exposed patient has more than one thyroid nodule.
  • Performing FNAB on only the two largest nodules would miss a significant number of malignant tumors and nodules smaller than 1 cm (0.4 inch) in diameter should be biopsied.
  • Over half of the patients with thyroid cancer had multiple tumors that involved both thyroid lobes.
  • There is an inverse relationship between the number of malignant and benign nodules, but why this occurs is uncertain.

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