Sequential 18 F-FDG PET/CT imaging parameters for differentiating benign from malignant lymph nodes in head and neck carcinoma.

Objective: The aim of this study was to differentiate between benign and malignant head and neck lymph nodes by sequential imaging.
Subjects and Methods: The total of 56 retrospectively analysed patients with suspected or histopathologically confirmed head and neck malignancy (nasopharyngeal cancers mainly; 28 patients), before any treatment, underwent sequential fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ( ¹⁸ F-FDG PET/CT) examinations for staging purposes. Remaining 28 patients with physiologic and histopathologically confirmed inflammatory (of non-specified origin) lymph nodes were included into this analysis. Patients underwent sequential PET/CT scans 60 and 90min post injection (p.i.) of the ¹⁸ F-FDG. Semi-quantitative analysis of metabolic activity within lymph nodes was based on the standardized uptake value (SUV) evaluation. To compare the metabolic activity fluctuation over time, the retention index (RI) was used. For SUV value and RI cut-off evaluation, the receiver operating characteristic (ROC) analysis was performed.
Results: The SUVmax value at 60min p.i. of physiologic, inflammatory and malignant (metastatic) lymph nodes were 1.09±0.33, 2.36±0.60 and 6.31±2.74, respectively. The SUVmax value at 90min p.i. were: 1.01±0.32, 2.48±0.61, and 7.17±2.91, respectively, and there was statistically significant difference between physiologic and inflammatory and physiologic and the metastatic lymph nodes (P<0.001). The values of early and delayed SUVmax were significantly different between physiologic and inflammatory and physiologic and metastatic lymph nodes (P<0.001). The SUVmax, SUVmean values at 60 and at 90min p.i. between malignant and inflammatory lymph nodes were statistically insignificant (P=0.33). The RI at 60 and at 90min p.i. was: -6%±16% for physiologic, 6%±14% for inflammatory and 15%±13% for the metastatic lymph nodes. The SUVmax changes over time (the RI) were statistically significant for physiologic and metastatic and physiologic and inflammatory lymph nodes (P<0.001) and significant between malignant and inflammatory lymph nodes (P=0.02).
Conclusion: Sequential delayed ¹⁸ F-FDG PET/CT examinations may increase specificity of this scan and provide information for the differentiation benign and malignant lymph nodes in the cases of head and neck cancer.