Introduction/Background The predominant treatment of vulval cancer is surgery, which carries significant morbidities, mainly lower limb lymphoedema. FIGO staging requires a histopathological dissection of the primary tumour and the inguinofemoral lymph nodes (IFLN). Metastasis to IFLN constitutes stage 3 cancer. Radiological methods of IFLN assessment often lack accuracy.In this study we report on the use of [¹⁸F] FDG-PET/CT to determine its accuracy as a pre-operative assessment tool for the groin in vulval squamous carcinoma. This could be beneficial in preoperative assessment to facilitate sentinel lymph node assessment, thus sparing the patient the morbidity associated with full lymphadenectomy.

Methodology This retrospective study analysed the data of 200 patients with vulval cancer, treated in St. James’s Hospital Dublin between 2010 and 2022. The predictive value of PET/CT in preoperative assessment of the groin node metastasis was assessed. SUVmax of the nodal uptake of each inguinal area (if present) was calculated and correlated to histologically confirmed groin metastasis. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of PET/CT in predicating groin node metastasis were calculated.

Results Out of the 200 patients 149 patients had unilateral or bilateral lymphadectomy and a preoperative PET scan resulting in 197 groins with full histopathological assessment of inguinal area and a PET/CT. 46 groins(23.3%) had histologically confirmed groin metastasis, of which 27 groins(58.7%) had positive PET/CT. The sensitivity of PET/CT for IFLN metastasis was 58.7% and specificity was 91.4%. The PPV was 67.5% and the NPV was 87.9%. The mean SUVmax was 6.5(range 1.6–30.0) for metastatic nodes (true positive) and 2.4(range 1.9–3.1) for negative nodes (false positive).

Conclusion This study showed that PET/CT was not sensitive enough to identify those at risk of lymph node metastasis. High NPV validates the use of PET-CT in discriminating metastatic from non-metastatic LNs, sparing patients unnecessary IFLN excision.