Diagnostic accuracy of 18F-FDG PET/CT in staging of salivary gland cancer

The purpose of this study was to evaluate the role of FDG PET/CT in staging and restaging of salivary gland cancer. PET/CT images obtained from November 2003 to June 2007 of pathologically proven salivary gland cancer patients were reviewed for primary salivary gland cancer, local recurrence, or local lymph node (LN) metastasis. All lesions with FDG uptake distinctive from the background activity were considered positive. The peak standard uptake values (pSUV) of suspected lesions were recorded. The PET/CT findings were compared with the histological or clinical and other imaging modality (CT or MRI) follow-up results. Total of 37 PET/CT images of 25 patients were included. Pathologic confirmation was available from 20 cases. 15 cases were concluded as positive, 6 out of 8 staging cases, and 9 out of 29 restaging cases. The overall sensitivity, specificity, positive and negative predictive values of FDG PET/CT for primary salivary gland cancer and local recurrence were 84.6%, 58.3%, 52.4% and 87.5%, respectively, and for local LN metastasis were 83.3%, 77.4%, 41.7% and 96.0%. For restaging, the sensitivity was 77.8% and specificity was 50.0%. There were 5 patients with distant metastasis demonstrated in PET/CT images, all in the lungs. The pSUV between the malignancy positive group and negative group was not statistically significance for the primary tumor or local recurrence site (5.03.0 versus 4.33.4, p=0.611), nor for local LN (3.7 1.6 versus 2.6 0.7, p=0.139). There were 2 malignant tumor cases with imperceptible FDG uptake in the recurrent tumor, and 1 case of LN metastasis also with imperceptible FDG uptake. On the other hand, there were 2 false positive (FP) staging cases, 2 FP restaging cases, and 2 FP LN metastasis cases with SUV greater than 3.0. The diagnostic accuracy of PET/CT in staging and restaging of salivary gland cancer is relatively low, but PET/CT incidentally detected distant metastasis in 13.5% of the cases