The usefulness of standardized uptake value in differentiation between benign and malignant thyroid lesions detected incidentally in 18F-FDG PET/CT examination

PLoS One. 2014 Oct 8;9(10):e109612. doi: 10.1371/journal.pone.0109612. eCollection 2014.

Abstract

Introduction: In the last decade, (18)F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET and PET/CT) has become one of the major diagnostic tools used in oncology. A significant number of patients who undergo this procedure, due to non-thyroidal reasons, present incidental uptake of (18F-FDG) in the thyroid. The aim of the study was to compare the SUVmax (standardized uptake value) of thyroid focal lesions, which were incidentally found on PET/CT, in relation to the results of thyroid fine-needle aspiration biopsy (FNAB) and/or histopathological evaluation.

Materials and methods: Patients referred for PET/CT examination, due to non-thyroidal illness, presented focal 18F-FDG uptake in the thyroid and were advised to undergo ultrasonography (US), hormonal evaluation, FNAB and/or total thyroidectomy at our institution.

Results: 6614 PET/CT examinations performed in 5520 patients were analyzed. Of the 122 patients with focal thyroid 18F-FDG activity, 82 patients (67.2%) underwent further thyroid evaluation using FNAB. Benign lesions were diagnosed in 46 patients, malignant - in 19 patients (confirmed by post-surgical histopathology), while 17 patients had inconclusive results of cytological assessment. Mean SUVmax of benign lesions was 3.2±2.8 (median = 2.4), while the mean SUVmax value for malignant lesions was 7.1±8.2 (median = 3.5). The risk of malignancy was 16.7% for lesions with a SUVmax under 3, 43.8% for lesions with a SUVmax between 3 and 6, and 54.6% for lesions with a SUVmax over 6. In the group of malignant lesions, a positive correlation between the lesion's diameter and SUVmax was observed (p = 0.03, r = 0.57).

Conclusions: Subjects with incidental focal uptake of 18F-FDG in thyroid are at a high risk of thyroid malignancy. A high value of SUVmax further increases the risk of malignancy, indicating the necessity for further cytological or histological evaluation. However, as SUVmax correlated with the diameter of malignant lesions, small lesions with focal uptake of 18F-FDG should be interpreted cautiously.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport
  • Biopsy, Fine-Needle
  • Diagnosis, Differential
  • Fluorodeoxyglucose F18 / metabolism*
  • Humans
  • Incidental Findings*
  • Male
  • Middle Aged
  • Multimodal Imaging / standards*
  • Positron-Emission Tomography / standards*
  • Reference Standards
  • Sensitivity and Specificity
  • Thyroid Neoplasms / diagnosis*
  • Thyroid Neoplasms / metabolism
  • Thyroid Neoplasms / pathology
  • Tomography, X-Ray Computed / standards*

Substances

  • Fluorodeoxyglucose F18

Grants and funding

This study was supported by the State Committee for Scientific Research (grant no. N N402 545540 and 402/FNiTP/162/2009). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.