Diagnostic Criteria on F-18-FDGPET/CT for Differentiating Benign from Malignant Focal Hypermetabolic Lesions of Parotid Gland

Purpose We investigated PET/CT diagnostic criteria for differentiating benign from malignant parotid lesions with focal 18F-FDG uptake. Methods The subjects of the study were 272 patients who exhibited focal 18F-FDG uptake of the parotid gland. Sixtyeight pathologically confirmed parotid lesions from 67 patients were included. The maximum SUV (SUVmax), uptake patterns (homogeneous vs. heterogeneous), size measured by CT, maximum Hounsfield units (HUmax) and margins on CT (well vs. ill defined) of each parotid lesion on PET/CT images were compared with final diagnoses. Results Thirty-two parotid lesions were histologically proven to be malignant. There were significant differences in uptake patterns (cancer incidence, heterogeneous: homogeneous0 79.2%: 29.5%, p< 0.0001) and margins on CT (cancer incidence, ill: well defined084.4%: 13.3%, p< 0.0001) between benign and malignant lesions. The cancer risks of parotid lesions were 89.5% with heterogeneous uptake and illdefined margins, 70.6% with heterogeneous uptake or illdefined margins (no overlap in subjects) and 9.3% with homogeneous uptake and well-defined margins (p< 0.0001). When any lesion with heterogeneous uptake or ill-defined margins was regarded as malignant, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 90.6% (29/32), 80.6% (29/36), 80.6% (29/36), 90.6%(29/32) and 85.6%(58/68), respectively. For predicting malignancy, combined PET/CT criteria showed better sensitivity, NPV and accuracy than PET-only criteria, and had a tendency to have more accurate results than CT-only criteria. There were no significant differences in SUVmax, size or HUmax between benign and malignant lesions. Conclusion Uptake patterns and margins on CT are useful PET/CT diagnostic criteria for differentiating benign from malignant lesions.