Physiologic thymic uptake of 18F-FDG in children and young adults: A PET/CT evaluation of incidence, patterns, and relationship to treatment

Jacqueline Jerushalmi, Alex Frenkel, Rachel Bar-Shalom, Jabour Khoury, Ora Israel

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

18F-FDG uptake in the thymus, mainly related to hyperplasia after chemotherapy, has been described. Thymic uptake can challenge the accurate assessment of cancer patients by 18F-FDG imaging. The present study defines the incidence, patterns, and intensity of thymic 18F-FDG uptake in relationship to age and time after treatment in a large cohort of patients. Methods: A total of 559 consecutive 18F-FDG PET/CT studies in 160 patients (86 men, 74 women; age, 3-40 y) performed at baseline, during treatment, at the end of treatment, and during follow-up were retrospectively reviewed. PET/CT studies were assessed for the presence or absence (T+ or T-, respectively), pattern, and intensity (SUVmax) of increased 18F-FDG uptake in the anterior mediastinum, localized by the CT component to the thymus. The overall incidence of 18F-FDG avidity in the thymus in relationship to the patient's age and time after treatment administration were statistically evaluated. Results: There were 137 of 559 T+ studies (25%), with equal sex distribution. T+ studies were found in significantly younger patients (20.6±3 y vs. 27.4±8.4 y, P< 0.001). Most T+ patients (60%) showed an inverted V pattern of thymic uptake, with additional unilateral mediastinal extension in 24% and focal midline uptake in 16% of studies. T+ studies were encountered in 80% of patients younger than 10 y, compared with 8% of patients in the 31- to 40-y age group. There were 17% T+ studies at baseline, 6% during treatment, 8% at the end of treatment, and 27%-40% during follow-up. The average SUVmax of thymic 18F-FDG uptake was 3.73 ± 1.22. Conclusion: Thymic 18F-FDG uptake was found in 28% of the present study population, more frequently after treatment. T+ patients were significantly younger. Thymic uptake was found in 73% of untreated patients up to the age of 13 y and in 8% of patients in the fourth decade of life. Knowledge of this age- and treatmentrelated incidence of physiologic thymic 18F-FDG avidity can reduce the number of potential pitfalls in reporting PET/CT studies in cancer patients.

Original languageEnglish
Pages (from-to)849-853
Number of pages5
JournalJournal of Nuclear Medicine
Volume50
Issue number6
DOIs
StatePublished - 1 Jun 2009
Externally publishedYes

Keywords

  • FDG avidity
  • PET/CT
  • Thymus

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