IS There A Role of 18F-FDG PET/CT for Initial Staging of Rectal Cancer ?

Background: The management of the rectal cancer requires accurate initial staging. Besides routinely performed conventional imaging, during the last decade 18F-FDG PET/CT became a popular whole-body metabolic imaging for preoperative TNM classification. The purpose of the study was to evaluate the role of 18F-FDG PET/CT in the rectal cancer staging. Patients and methods: 45 patients with rectal cancer who preoperatively underwent 18F-FDG PET/CT imaging in the period from 2011 to 2014 were analyzed. All patients were referred to the surgery afterwards. Histopathologic findings were used as a standard of reference. Descriptive techniques were used for frequency analyses and sensitivity calculations. The χ2 test was used for significance calculation of the contingency tables while Monte Carlo simulation and Fisher's exact test were used for the table fields where number of cases was smaller than demanded. Results: The average SUVmax value of the primary tumor for all T stages was 26.02 gm/mL. The average SUVmax values of the lymph nodes in N1 stage and N2 stage were 6.04 gm/mL and 6.33 gm/mL, respectively. PET/CT detected benign lesions in 17 (28.3%) patients with average SUVmax of 15.4 mg/mL. The vaginal wall infiltration was detected in 2 (4.4%) patients. Penetration of mesorectal fascia was detected in 21 (46.7%) of patients. Four patients (8.9%) had liver metastases identified by 18F-FDG PET/CT. The overall sensitivity, specificity and accuracy of 18F-FDG PET/CT in T staging was 90.7%, 91.9%, and 90.5%, respectively. The overall sensitivity, specificity and accuracy of 18F-FDG PET/CT in detection of metastatic lymph node was 85.8%, 89.8%, and 89%, respectively. PET/CT shows low sensitivity (77.3%) and specificity (25%) in analyzing mesorectal fascia involvement. The overall sensitivity of 18F-FDG PET/CT in M staging was 100%. Conclusions: 18F-FDG PET/CT is highly sensitive for initial T staging of rectal cancer especially in advanced disease. This imaging modality is highly accurate in detection of metastatic lymph nodes and liver metastases, but it has no role in defining of mesorectal fascia involvement. Therefore, 18F-FDG PET/CT should be incorporated routinely in preoperative staging together with conventional imaging.