Multimodal imaging evaluation in staging of rectal cancer

Abstract

Rectal cancer is a common cancer and a major cause of mortality in Western countries. Accurate staging is essential for determining the optimal treatment strategies and planning appropriate surgical procedures to control rectal cancer. Endorectal ultrasonography (EUS) is suitable for assessing the extent of tumor invasion, particularly in early-stage or superficial rectal cancer cases. In advanced cases with distant metastases, computed tomography (CT) is the primary approach used to evaluate the disease. Magnetic resonance imaging (MRI) is often used to assess preoperative staging and the circumferential resection margin involvement, which assists in evaluating a patient’s risk of recurrence and their optimal therapeutic strategy. Positron emission tomography (PET)-CT may be useful in detecting occult synchronous tumors or metastases at the time of initial presentation. Restaging after neoadjuvant chemoradiotherapy (CRT) remains a challenge with all modalities because it is difficult to reliably differentiate between the tumor mass and other radiation-induced changes in the images. EUS does not appear to have a useful role in post-therapeutic response assessments. Although CT is most commonly used to evaluate treatment responses, its utility for identifying and following-up metastatic lesions is limited. Preoperative high-resolution MRI in combination with diffusion-weighted imaging, and/or PET-CT could provide valuable prognostic information for rectal cancer patients with locally advanced disease receiving preoperative CRT. Based on these results, we conclude that a combination of multimodal imaging methods should be used to precisely assess the restaging of rectal cancer following CRT.

Keywords: Rectal cancer; Multimodality; Imaging; Staging; Restaging

Core tip: In rectal cancer, accurate staging and circumferential resection margin assessment are essential for stratifying the risks of recurrence and determining the optimal therapeutic strategy for individual patients. In the preoperative setting, a combination of multimodal imaging methods, including endorectal ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI), can be used to precisely assess the preoperative staging of rectal cancer. However, restaging after neoadjuvant therapy remains a challenge with all of these modalities. Recently, high-resolution MRI with diffusion-weighted imaging and/or positron emission tomography-CT imaging methods have been developed to precisely assess the restaging of rectal cancer following neoadjuvant chemoradiation therapy.