Comparison of 18F-FDG PET/CT and MRI for detection of regional lymph node metastasis in vulvar cancer and vaginal cancer

Objectives: The most important factor in survival of vulvar and vaginal cancer is the presence of lymph node metastasis at the time of diagnosis. Undetected lymph node metastasis will often be fatal for the patients. The aim of this study, was to compare 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and magnetic resonance imaging (MRI) for the preoperative detection of regional lymph node metastases in patients with vulvar and vaginal cancer.

Methods: The prospective study reviewed patients diagnosed with primary and recurrent vulvar cancer or vaginal cancer between 2010 to 2015. Enrolled patients were preoperatively examined by FDG PET/CT and MRI. Subsequent histopathological analyses of regional removed lymph nodes were conducted.

Results: 83 patients were included in the study of which 66 patients were diagnosed with primary vulvar or vaginal cancer, while the remaining 17 patients were diagnosed with recurrence of vulvar or vaginal cancer. Statistical analysis was conducted on a patient basis on the total patient group, and on the group of patients with primary vulvar and vaginal cancer. For the total patient group, the sensitivity, specificity, accuracy, positive (PPV) and negative predictive value (NPV) of FDG PET/CT for detection of nodal disease using SUVmax cut-off of 2 were determined to 89%, 67%, 78%, 55 %, and 93%. In patients with primary cancer the sensitivity, specificity, accuracy, PPV and NPV for FDG PET/CT and were 90%, 61%, 75%, 50%, and 93% using the same cut-off for SUVmax. From Receiver operating characteristics (ROC) analysis of the total group, an optimum SUVmax cut-off value of 3.77 was identified providing a sensitivity, specificity, accuracy, PPV and NPV of 77 %, 79 %, 78%, 63 %, and 88 %. In comparison, the sensitivity, specificity, accuracy, PPV and NPV for MR for the total group and the group of primary disease were 53%; 90%; 72%, 70%; 81% and 50%, 89%, 70%, 67%, 80%, respectively. The area under the ROC curve for FDG PET/CT and MRI were 0.776 and 0.717, respectively (P = 0.297). While FDG PET/CT showed a significantly higher sensitivity for detecting metastatic lymph nodes than MRI (P = 0.003), MRI showed a significantly higher specificity compared to FDG PET/CT (P = 0.001).

Conclusions: FDG PET/CT was found to have higher sensitivity and NPV compared to MRI in detecting regional metastatic lymph nodes in patients with vulvar and vaginal cancer. However, MRI was found to have higher specificity and PPV as compared to FDG PET/CT. As the area under the ROC curves of PET/CT and MRI were not significantly different, it is concluded that neither technique is superior to the other in detection of lymph node metastases in patients with vulvar and vaginal cancer.