Clinical significance of thyroid uptake on F18-fluorodeoxyglucose positron emission tomography

Ann Nucl Med. 2009 Jan;23(1):17-23. doi: 10.1007/s12149-008-0198-0. Epub 2009 Feb 11.


Significant uptake of the thyroid is often identified as an incidental finding on whole-body F18-fluorodeoxyglucose positron emission tomography (FDG-PET) for non-thyroid disease. Sometimes, it is a dilemma for radiologists to interpret clinical significance of thyroid uptake and give adequate recommendation for further evaluation. In general, diffuse uptake of the thyroid glands on FDG-PET is considered to be benign and very likely secondary to thyroiditis and/or hypothyroidism; a further correlation or investigation of the thyroid function and/or ultrasound is helpful. Focal uptake of the thyroid on FDG-PET is defined as an incidentaloma, which is more clinically significant owing to its high risk of malignancy ranging 25-50%. Although maximum standardized uptake value and corresponding computed tomographic finding may help to differentiate benign from malignant lesion, a cytological diagnosis is often advised. The clinical significance of diffuse plus focal uptake of the thyroid on FDG-PET is not well known; it may also be associated with an increased risk of malignancy when compared with a diffuse uptake pattern only.

Publication types

  • Review

MeSH terms

  • Fluorodeoxyglucose F18 / pharmacokinetics*
  • Humans
  • Incidental Findings
  • Positron-Emission Tomography / methods*
  • Radiopharmaceuticals / pharmacokinetics
  • Thyroid Diseases / diagnosis*
  • Thyroid Gland / diagnostic imaging*
  • Thyroid Gland / metabolism*
  • Whole Body Imaging / methods*


  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18