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

Figure 1

Endorectal ultrasound image of T3 rectal cancer. Endorectal ultrasonography image shows a hypo-echoic mass (arrows) that extends into the echogenic mesorectal fat (arrowheads).

Figure 2

Stage T2 and T3 rectal cancer detected by magnetic resonance imaging. A: T2-weighted magnetic resonance image shows an intraluminal polypoid mass (arrows) confined to the intact, hypo-intense muscularis propria (arrowheads), suggestive of a T2 cancer; B: T3 lesion is seen as a tumor (arrows) that extends through the hypo-intense muscle layer into the perirectal fat (arrowheads).

Figure 3

Mesorectal fascia invasion detected by magnetic resonance imaging. T2-weighted magnetic resonance image shows a T3 tumor (arrows) with involvement of the mesorectal fascia (arrowheads).

Figure 4

Over-staging due to post-chemoradiotherapy changes. T2-weighted image obtained after chemoradiotherapy shows hypo-intense infiltration (arrows) to the perirectal fat and a spiculated lymph node (arrowheads), which was misinterpreted as a remnant T3 lesion and metastatic node. However, there was neither a residual tumor nor metastatic lymph node on the pathological examinations after surgery.

Figure 5

Combination of high-resolution magnetic resonance imaging with diffusion-weighted imaging and positron emission tomography/computed tomography for assessing tumor response after neoadjuvant chemoradiotherapy. A-C: T2-weighted magnetic resonance image (MRI) (A), diffusion-weighted imaging (DWI) (B), and positron emission tomography (PET)/computed tomography (CT) (C) obtained before chemoradiotherapy (CRT) shows a T3 tumor (arrows) with the restricted diffusion and intense hyper-metabolism; D-F: After CRT, T2-weighted MRI (D) shows a marked decrease in the tumor size. DWI (E) shows the focal diffusion restriction confined to the rectal wall, corresponding to histological proven T2 lesion. PET/CT (F) also demonstrates the good tumor response to CRT.