[Imaging modalities in the assessment of presacral recurrent rectal cancer]

Imaging plays a key role in the diagnosis and decision-making process including pre-treatment planning, surgical strategy, and follow-up. The critical point in diagnosis of presacral recurrent rectal cancer by imaging modalities is to distinguish the recurrent tumor from nonmalignant tissues induced by operation or radiotherapy. The practice guideline recommends CT as surveillance imaging modality for recurrent rectal cancer. MRI shows higher accuracy, sensitivity, and specificity in diagnosis of presacral recurrent rectal cancer compared with CT. If CT or MRI can not make final diagnosis in challenging cases, 18-fluorodeoxyglucose positron emission tomography ((18)FDG PET) is recommended to aid diagnosis with high sensitivity and specificity, though false-positivity and negativity should be considered. If new or enlarging soft tissue are shown in the follow-up examination, tumor recurrence should be suspected. In addition, tumor-related high risk factors, treatment protocol, surgery, quality of specimen and pathological stages should also be considered when presacral recurrent rectal cancer is to be diagnosed.