Endocrinol Metab.  2015 Mar;30(1):71-77. 10.3803/EnM.2015.30.1.71.

Risk of Malignancy in Thyroid Incidentalomas Identified by Fluorodeoxyglucose-Positron Emission Tomography

• Chun AR
• Jo HM
• Lee SH
• Chun HW
• Park JM
• Kim KJ
• Jung CH
• Mok JO
• Kang SK
• Kim CH
• Kim BY

• KMID: 2407107
• DOI: http://doi.org/10.3803/EnM.2015.30.1.71

Abstract

BACKGROUND
Thyroid incidentalomas detected by 2-deoxy-2-18F-fluoro-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) have been reported in 1% to 4% of the population, with a risk of malignancy of 27.8% to 74%. We performed a retrospective review of FDG-avid thyroid incidentalomas in cancer screening subjects and patients with nonthyroid cancer. The risk of malignancy in thyroid incidentaloma and its association with the maximal standardized uptake value (SUVmax) in 18F-FDG PET/CT were evaluated to define the predictor variables in assessing risk of malignancy.
METHODS
A total of 2,584 subjects underwent 18F-FDG PET/CT for metastatic evaluation or cancer screening from January 2005 to January 2010. Among them, 36 subjects with FDG-avid thyroid incidentalomas underwent further diagnostic evaluation (thyroid ultrasonography-guided fine needle aspiration cytology [FNAC] or surgical resection). We retrospectively reviewed the database of these subjects.
RESULTS
Of the 2,584 subjects who underwent 18F-FDG PET/CT (319 for cancer screening and 2,265 for metastatic evaluation), 52 (2.0%) were identified as having FDG-avid thyroid incidentaloma and cytologic diagnosis was obtained by FNAC in 36 subjects. Of the subjects, 15 were proven to have malignant disease: 13 by FNAC and two by surgical resection. The positive predictive value of malignancy in FDG-avid thyroid incidentaloma was 41.7%. Median SUVmax was higher in malignancy than in benign lesions (4.7 [interquartile range (IQR), 3.4 to 6.0] vs. 2.8 [IQR, 2.6 to 4.0], P=0.001).
CONCLUSION
Thyroid incidentalomas found on 18F-FDG PET/CT have a high risk of malignancy, with a positive predictive value of 41.7%. FDG-avid thyroid incidentalomas with higher SUVmax tended to be malignant.

Keyword

Thyroid gland; Incidental findings; Fluorodeoxyglucose F18; Positron-emission tomography; Thyroid neoplasms; Prevalence

MeSH Terms

Biopsy, Fine-Needle
Diagnosis
Early Detection of Cancer
Electrons
Fluorodeoxyglucose F18
Humans
Incidental Findings
Positron-Emission Tomography
Positron-Emission Tomography and Computed Tomography
Prevalence
Retrospective Studies
Thyroid Gland*
Thyroid Neoplasms
Fluorodeoxyglucose F18

Figure

• 

  Fig. 1 Selection of patients from those who underwent 2-deoxy-2-18F-fluoro-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT) for cancer screening and metastatic evaluation was based on the presence of focal FDG-avid thyroid incidentaloma. FNAB, fine needle aspiration biopsy; US, ultrasonography.

• 

  Fig. 2 A 60-year-old man with underlying sigmoid colon cancer. (A) A focal fluorodeoxyglucose-avid lesion with calcification was incidentally detected in the right lobe of the thyroid (posterior-anterior view). (B) Fusion axial positron emission tomography/computed tomography image showing a hypermetabolic lesion and calcification in the right lobe of the thyroid gland (maximal standardized uptake value=2.6).

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