Contribution of PET/CT in Determining Lymph Node Metastasis Before Low Anterior Resection

The aim of this study was to evaluate the sensitivity of 18F-FDG (fluorodeoxyglucose) PET/CT (positron emission tomography / computed tomography) imaging performed for primary staging prior to surgery performed with the low anterior resection technique in detecting the presence of lymph node metastases detected in the mesorectal area. In our retrospective study, 44 patients who were operated for colorectal cancer in our Surgical Oncology Department between June 15, 2015 and June 15, 2020 and who underwent 18F-FDG PET/CT for preoperative staging were included. The demographic data of the patients were obtained from the records were taken during routine clinical interrogations before both surgery and PET/CT scan, and from the automation system records of our hospital. While 12 (27.3%) of the patients had vascular invasion, 32 (72.7%) did not. While 15 (34.1%) of the patients had perineural invasion, 29 (65.9%) did not. Histopathologically, the rates of lymph node metastasis were high in patients with vascular invasion and perineural invasion (p=0.005 and p=0.012, respectively). There was no significant relationship between the SUVmax value of the primary tumor in PET/CT and the presence/absence of lymph node metastasis histopathologically determined (p=0.405). The median tumor size of the primary mass lesion was 4 cm (15-150 mm). No significant correlation was found between tumor size and presence/absence of lymph node metastasis (p=0.587). Sensitivity of CT is 68.7%, specificity 44.4%, accuracy 55.8%, positive predictive value 52.3%, negative the predictive value was 61.5%; whereas the sensitivity of 18F-FDG PET/CT was found to be 78.9%, specificity 50%, accuracy 63.6%, positive predictive value 55.5%, negative predictive value 76.4%. In conclusion, despite advanced imaging techniques, it will not be possible to be sure of the presence/absence of metastatic lymph nodes without radical surgery. We think that PET/CT imaging has also an important place in determining distant lymph node metastases other than regional lymph node spread.