Roles of MRI evaluation of pelvic recurrence in patients with rectal cancer.

Developments in the multidisciplinary treatment of rectal cancer with advances in preoperative magnetic resonance imaging (MRI), surgical techniques, neoadjuvant chemoradiotherapy, and adjuvant chemotherapy have had a significant impact on patient outcomes, increasing the rates of curative surgeries and reducing pelvic recurrence. Patients with pelvic recurrence have worse prognoses, with an impact on morbidity and mortality. Although local recurrence is more frequent within 2 years of surgical resection of the primary tumor, late recurrence may occur. Clinical manifestations can vary from asymptomatic, nonspecific symptoms, to pelvic pain, bleeding, and fistulas. Synchronous metastatic disease occurs in approximately 50% of patients diagnosed with local recurrence. MRI plays a crucial role in posttreatment follow-up, whether by identifying viable neoplastic tissues or acting as a tool for therapeutic planning and assessing the resectability of these lesions. Locally recurrent tissues usually have a higher signal intensity than muscle on T2-weighted imaging. Thus, attention is required for focal heterogeneous lesions, marked contrast enhancement, early invasive behavior, and asymmetric appearance, which are suspicious for local recurrence. However, postsurgical inflammatory changes related to radiotherapy and fibrosis make it difficult to detect initial lesions. This study therefore aimed to review the main imaging patterns of pelvic recurrence and their implications for the surgical decision-making process. CRITICAL RELEVANCE STATEMENT: MRI plays a crucial role in the posttreatment follow-up of rectal cancer, whether by identifying viable neoplastic tissues or by acting as a tool for therapeutic planning. This study reviewed the main imaging patterns of pelvic recurrence. KEY POINTS: MRI aids in surgical planning and the detection of pelvic recurrence and postoperative complications. Being familiar with surgical techniques enables radiologists to identify expected MRI findings. Patterns of rectal cancer recurrence have been categorized by pelvic compartments. Neoplastic tissue may mimic postsurgical and postradiotherapy changes. Resectability of pelvic recurrence is highly related to lesion location.