Study: Negative FDG PET/CT can rule out thyroid surgery
A negative 18FDG PET/CT scan rules out malignancies among thyroid nodules with nondiagnostic cytology, according to a study published online April 7 in Clinical Endocrinology.

The evaluation of patients with thyroid nodules typically includes measurement of serum thyrotrophin and ultrasound-guided fine-needle cytology. The objective of the study was to assess the role of 18FDG PET/CT scans in the evaluation of thyroid nodules with nondiagnostic cytology, according to Luca Giovanella, MD, from the department of nuclear medicine and thyroid center at the Oncology Institute of Southern Switzerland in Bellinzona.

Eighty-eight patients with a single euthyroid nodule and repeatedly nondiagnostic ultrasound-guided fine-needle cytology were enrolled in the study. 18FDG PET/CT, lobectomy and histological analysis of the surgical specimens were performed in the specified order in all patients by Giovanella and colleagues.

Nodules concentrating 18FDG were considered positive and histological findings were obtained after surgery in all patients. None of the 41 patients with a negative 18FDG PET/CT scan had a final histological diagnosis of malignancy; there were no false negative results, according to Giovanella and colleagues.

Twenty-nine patients with final histological diagnosis of thyroid cancer had positive 18FDG PET/CT scans. Eighteen patients with a final histological diagnosis of benign lesions (including four with follicular adenomas) also had positive 18FDG PET/CT scans. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value were 100 percent,  69 percent, 79 percent, 62 percent and 100 percent, respectively.

“Even if a positive 18FDG PET/CT scan cannot differentiate benign and malignant follicular lesions, a negative one is more effective than other procedures to rule out surgery,” wrote Giovanella and colleagues.

Finally, all patients with diffuse or diffuse plus focal 18FDG thyroid uptake had a final diagnosis of autoimmune thyroiditis. Consequently, both diffuse and diffuse plus focal 18FDG uptake pattern on PET/CT might be associated with a benign condition, noted the authors.

Histology is still necessary to distinguish benign from malignant disease in 18FDG PET/CT-positive nodules, but unnecessary surgery could have been reduced from 88 to 41 cases (46 percent) in this series, according Giovanella and colleagues. “Even if a detailed cost analysis was not one of our aims, this enhances resource optimization and positively impacts on cost effectiveness,” concluded Giovanella and colleagues.