Thyroid nodules with indeterminate cytology: prospective comparison between 18F-FDG-PET/CT, multiparametric neck ultrasonography, 99mTc-MIBI scintigraphy and histology

Abstract

Purpose To evaluate the role of 18F-flurodeoxiglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) in predicting malignancy of thyroid nodules with indeterminate cytology. Patients and methods We analysed 87 patients who have been scheduled to undergo surgery for thyroid nodule with indeterminate cytology. All patients underwent 18F-FDG-PET/CT, multiparametric neck ultrasonography (MPUS), and 99mTc-methoxyisobutylisonitrile scintigraphy (99mTc-MIBI-scan). Histopathology was the standard of reference. We compared the sensitivity (SE), specificity (SP), accuracy (AC), positive (PPV) and negative predictive (NPV) values of 18F-FDG-PET/CT with those of 99mTc-MIBI-scan and MPUS in detecting cancer. Univariate and multivariate analyses evaluated the association between each diagnostic tool and histopathology. Results On histopathology, 69 out of 87 nodules were found to be benign and 18 to be malignant. The SE, SP, AC, PPV and NPV of 18F-FDG-PET/CT were 94, 58, 66, 37 and 98% respectively. The SE, AC and NPV of 18F-FDG-PET/CT were significantly higher than those of MPUS and 99mTc-MIBI-scan. The association of both positive 18F-FDG-PET/CT and MPUS (FDG+/MPUS+) showed significantly lower SE (61% vs 94%) and NPV (88% vs 98%) than 18F-FDG-PET/CT alone, but significantly higher SP (77% vs 58%). On univariate analysis, 18F-FDG-PET/CT and the combination of FDG+/MPUS+ and of FDG+/MIBI− were all significantly associated with histopathology. On multivariate analysis, only FDG+/MIBI− was significantly associated with histopathology. Conclusion The AC of 18F-FDG-PET /CT in detecting thyroid malignancy is higher than that of 99mTc-MIBI-scan and MPUS. A negative 18F-FDG-PET/CT correctly predicts benign findings on histopathology. The association of FDG+/MPS+ is significantly more specific than 18F-FDG-PET/CT alone in identifying differentiated thyroid cancer. A positive 18F-FDG-PET/CT is significantly associated with malignancy when qualitative 99mTc-MIBI-scan is rated as negative.