Prospective evaluation of solitary thyroid nodule on 18F-FDG PET/CT and high-resolution ultrasonography.
OBJECTIVE
The utility of 18F-FDG PET/CT in the assessment of thyroid nodules is unclear as there are several conflicting reports on the usefulness of SUV as an indicator to distinguish benign from malignant thyroid lesions. This study incorporated an additional parameter, namely dual time point imaging, to determine the diagnostic accuracy of PET/CT imaging. The performance of 18F-FDG PET/CT was compared to that of high-resolution ultrasound which is routinely used for the evaluation of thyroid nodules.


METHODS
Two hundred patients with incidentally detected solitary thyroid nodules were included in the study. Each patient underwent ultrasound and PET/CT evaluation within 7 days of each other, reported by an experienced radiologist and nuclear medicine specialist, respectively, in a blinded manner. The PET/CT criteria employed were maximum SUV (SUV(max)) at 60 min and change in SUV(max) at delayed (120 min) imaging. Final diagnosis was based on pathological evaluation and follow-up.


RESULTS
Of the 200 patients, 26 had malignant and 174 had benign nodules. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of ultrasound were 80.8, 81.6, 39.6, 96.6 and 81.5%, respectively. Using SUV(max) at 60 min as the diagnostic criterion, the above indices were 80.8, 84.5, 43.8, 96.7 and 84%, respectively, for PET/CT. The SUV(max) of malignant thyroid lesions was significantly higher than benign lesions (16.2 +/- 10.6 vs. 4.5 +/- 3.1, respectively; p = 0.0001). Incorporation of percentage change in SUV(max) at delayed imaging as the diagnostic criterion yielded a slightly improved sensitivity, specificity, PPV, NPV and accuracy of 84.6, 85.6, 46.8, 97.4 and 85.5%, respectively. There was a significant difference in percentage change in SUV(max) between malignant and benign thyroid lesions (14.9 +/- 11.4 vs. -1.6 +/- 13.7, respectively; p = 0.0001). However, there was no statistically significant difference (95% confidence interval) between the diagnostic performance of PET/CT and ultrasound.


CONCLUSIONS
Routine use of 18F-FDG PET/CT with SUV(max) at 60 min as the sole diagnostic criterion does not appear to have a significant advantage over high-resolution ultrasound in the evaluation of thyroid nodules. Incorporation of dual time point imaging enhances image interpretation, and yields a higher diagnostic performance, yet it is not statistically significant. Bearing in mind the cost, limited availability and radiation exposure, routine use of 18F-FDG PET/CT for distinguishing benign from malignant thyroid nodules cannot be recommended.
D'Souza
Maria Mathew
MM
Division of PET Imaging, Molecular Imaging and Research Centre, Institute of Nuclear Medicine and Allied Sciences, Delhi, 110054, India. maria.md@rediffmail.com
Marwaha
Raman Kumar
RK
Sharma
Rajnish
R
Jaimini
Abhinav
A
Thomas
Shaji
S
Singh
Dinesh
D
Jain
Manjula
M
Bhalla
Param Jit Singh
PJ
Tripathi
Madhavi
M
Tiwari
Anjani
A
Mishra
Anil
A
Mondal
Anupam
A
Tripathi
Rajendra Prashad
RP
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D003937:Diagnosis, Differential; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D012372:ROC Curve; D016606:Thyroid Nodule / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D055815:Young Adult
D019788:Fluorodeoxyglucose F18