Diagnostic Usefulness of 18F-FDG PET/CT in Differentiated Thyroid Cancer Patients with Elevated Serum Thyroglobulin or Thyroglobulin Antibody Levels
Chalermrat Kaewput MD*, Pawana Pusuwan MD*
Affiliation : * Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective : To evaluate diagnostic accuracy of 18F-FDG PET/CT in detection of recurrence or metastases in differentiated
thyroid cancer (DTC) patients with elevated stimulated thyroglobulin (sTg) or thyroglobulin antibody (TgAb) levels but
negative 131I whole body scan (131I WBS).
Material and Method: Between January 2007 and December 2014, 38 18F-FDG PET/CT examinations in 38 DTC patients
with elevated sTg levels (10 ng/ml or greater, n = 33) or elevated TgAb levels (40.0 IU/ml or greater, n = 5) but negative
post-therapeutic 131I WBS or diagnostic 131I WBS were included. All patients underwent total thyroidectomy and radioiodine
ablation. The 18F-FDG PET/CT findings were compared with histologic (n = 16) or clinical follow-up results based on
serum Tg/TgAb levels or other imaging modalities. Duration of follow-up ranged from six months to seven years (median
duration = 30 months).
Results : Thirty-two studies showed true positive lesions of local recurrence (n = 23, 60.5%), distant metastases (n = 2,
5.3%) and both local recurrence and distant metastases (n = 7, 18.4%). One study (2.6%) was considered as false positive
lesions at cervical nodes, which was confirmed by histological result. Four studies (10.5%) were confirmed true negative
results. A patient with no abnormal 18F-FDG avidity in subcentimeter cervical lymph nodes was clarified as false negative,
as subsequent follow-up results showed slow rising of Tg levels with suggestion of cervical node metastases demonstrated
by neck ultrasonography. Sensitivity, specificity, and accuracy of 18F-FDG PET/CT in the present study were 96.9%, 80%,
and 94.7%, respectively. Additional information of previously undiagnosed lesions was found in seven patients i.e.,
meningioma and metastatic lesions in brain, bone, liver, muscle, and soft tissue.
Conclusion : The 18F-FDG PET/CT is useful for detection and localization of recurrence or metastases in DTC patients
with negative 131I WBS but elevated sTg or TgAb levels. This technique also provides useful additional findings for appropriate
management of these patients.
Keywords : Thyroid carcinoma, 18F-FDG PET/CT, Thyroglobulin, 131I whole body scan
