FDG-avid presacral soft tissue mass in previously treated rectal cancer: Diagnostic outcome and additional value of MRI, including diffusion-weighted imaging

Introduction: This study aimed to determine the positive predictive value (PPV) of positron emission tomography/computed tomography (PET/CT) with an F-18-fluoro-2-deoxy-D-glucose (FDG)-avid presacral lesion for locally recurrent rectal cancer, and the additional value of magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI). Materials and methods: This retrospective study included 38 patients who completed primary rectal cancer treatment and who presented with a suspicious FDG-avid presacral lesion on PET/CT. Twenty-seven patients also underwent MRI, of whom 24 with DWI. PPV of FOG-PET/CT and additional value of MRI, including DWI, for the diagnosis of recurrent presacral cancer were determined. Results: The PPV of PET/CT with an FDG-avid presacral lesion for the diagnosis of locally recurrent rectal cancer was 58% (22/38). Air in the FDG-avid presacral lesion, as visible on the a component of the PET/CT examination, favoured the diagnosis of benign presacral tissue with a sensitivity of 56.3% (9/16) and a specificity 81.8% (18/22). Areas under the receiver operating characteristic curve (AUCs) of MRI without DWI for the diagnosis of locally recurrent rectal cancer in FDG-avid presacral tissue were 0.765 and 0.840, for observers 1 and 2. AUCs of MRI with DWI were 0.803 and 0.811, for observers 1 and 2. There were no significant differences among any of these AUCs (P=0.169 to 0.906). Conclusions: FOG-PET/CT has a poor PPV for locally recurrent rectal cancer in the presacral space. The observation of air in the FDG-avid presacral lesion and additional MRI assessment are diagnostically helpful, without a significant additional value of DWI. (C) 2018 Elsevier Ltd, BASO similar to The Association for Cancer Surgery, and the European Society of Surgical Oncology. All rights reserved