Differentiation between peri-anastomotic inflammatory changes and local recurrence following neoadjuvant radiochemotherapy surgery for colorectal cancer using visual and semiquantitative analysis of PET-CT data

Aim. The aim of this study was to evaluate the usefulness of visual and semiquantitative [F-18]fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) data for the diagnosis of peri-anastomotic colorectal cancer recurrence, taking into account the time period between surgery and [F-18]FDG PET-CT scanning. Methods. The study population consisted of 70 patients who had prior preoperative radiochemotherapy and surgical resection of the primary tumor and who underwent whole body [F-18]FDG PET-CT scanning for the detection of recurrent disease. Visual and semiquantitative (SUVmax) analysis of [F-18]FDG uptake at the peri-anastomosis was performed. The final diagnosis was based on pathological proof or clinical and/or imaging follow-up data. Results. On visual reading, 27 patients exhibited increased [F-18]FDG uptake at the peri-anastomosis. Of these, 11 (41%) patients had a local tumor recurrence and 16 (59%) had no recurrent tumor. Among the 43 patients without increased [F-18]FDG uptake at the peri-anastomosis, none had local tumor recurrence. On semiquantitation, SUVmax in patients with and without a local recurrence overlapped. However, when the time period between surgery and [F-18]FDG PET-CT scanning was taken into account, overlap of SUVmax was mainly observed within a postoperative period of <= 12 months; thereafter, a threshold SUVmax of 3.2 discriminated between benign and malignant lesions in all but one patient. Conclusion. In our series, visually increased [F-18]FDG uptake at the peri-anastomosis was 100% sensitive but non-specific (73% specificity) for the diagnosis of local tumor recurrence. On the other hand, normal [F-18]FDG uptake at the peri-anastomosis precluded a local tumor recurrence (a negative predictive value of 100%). In addition, semiquantitative (SUVmax) analysis of [F-18]FDG uptake at the peri-anastomosis may increase specificity (up to 97%), while preserving maximum sensitivity, if the postoperative period is >12 months.