F18-FDG PET/CT accuracy in nodal staging of head and neck squamous cell carcinoma and correlation of SUVmax to the likelihood of a confirmed nodal metastasis

Introduction: This study aimed to determine F18-Fluorodeoxyglucose Positron Emission Tomography/ Computerised Tomography (FDG-PET/CT) accuracy in nodal staging of head and neck squamous cell carcinoma (HNSCC) and investigate the relationship between increasing standard uptake value max (SUVmax) thresholds and the likelihood of a diagnosis of nodal malignancy on histopathological analysis. Methods: Histopathological diagnosis was correlated retrospectively with the reported nodal involvement on PET/CT scans. Data was analysed to determine the accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). SUVmax was measured for the most FDG-avid node in the nodal levels noted to be malignant on histopathological analysis and for those deemed malignant in the PET/CT report. A range of SUVmax thresholds was then applied retrospectively to calculate the corresponding likelihood of a node being truly malignant. Results: The "per lymph node level " analysis (n = 216) found accuracy of 81.5%, sensitivity of 68.8%, specificity of 85.1%, PPV of 59.9% and NPV of 90.5%. A strong positive correlation was found between the threshold SUVmax and the likelihood of a diagnosis of malignancy on histopatho-logical analysis. A significant increase in likelihood from 72.2% to 83.3% was found when the SUVmax threshold was increased from 4.0 to 4.5. Conclusion: This study reinforces the utility of PET/CT as a diagnostic tool for ruling out malignant nodal dissemination due to its high NPV. Secondly, it shows a strong positive correlation between SUVmax of the lymph node and its likelihood of being malignant, which may assist in determining which lymph nodes should be biopsied.