Restaging MRI of Rectal Adenocarcinoma after Neoadjuvant Chemoradiotherapy: Imaging Findings and Potential Pitfalls

Arterial Mucosal Linear Enhancement at Contrast-enhanced MRI to Exclude Residual Tumor after Neoadjuvant Chemotherapy and Radiation Therapy for Rectal Cancer

Background A watch-and-wait regimen for locally advanced rectal cancer after neoadjuvant chemotherapy and radiation therapy (NCRT) relies on identifying complete tumor response. However, the concordance between a complete response at combined T2-weighted and diffusion-weighted MRI (T2DWI) and pathologic complete response (pCR; ie, ypT0N0) in the tumor is unsatisfactory. Purpose To assess whether identification of mucosal linear enhancement (MLE) at arterial-phase contrast-enhanced (CE) T1-weighted MRI is associated with ypT0 status in patients with locally advanced rectal cancer after NCRT and to evaluate whether combining MLE at CE T1-weighted MRI and negative lymph node metastasis (LNM) at T2DWI can improve identification of pCR. Materials and Methods This retrospective study included patients with locally advanced rectal cancer who underwent total mesorectal excision after NCRT between July 2020 and July 2023 at a tertiary referral academic center. Restaging MRI included T2DWI and arterial-phase CE T1-weighted MRI for primary tumor assessment and T2DWI for evaluation of LNM status. Imaging features associated with ypT0 status were identified at multivariable regression analysis. Results In total, 239 patients (mean age, 58 years ± 12 [SD]; 180 male patients) were assessed. MLE was more common in the ypT0 group than in the ypT1-4 group after NCRT (73% vs 4%, respectively; P < .001). MLE was associated with higher odds of ypT0 status in an adjusted analysis (odds ratio, 137; 95% CI: 25, 767; P < .001). The combination of MLE and negative LNM status achieved an area under the receiver operating characteristic curve of 0.84 (95% CI: 0.79, 0.88) for pCR. Conclusion MLE at CE MRI was associated with higher odds of complete tumor response. Combining MLE and negative LNM status showed good performance for identifying complete tumor response and may exclude residual tumors after NCRT in patients with locally advanced rectal cancer. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Schoellnast in this issue.

Primary staging of rectal cancer on MRI: an updated pictorial review with focus on common pitfalls and current controversies

Magnetic resonance imaging (MRI) plays a pivotal role in primary staging of rectal cancer, enabling the determination of appropriate management strategies and prediction of patient outcomes. However, inconsistencies and pitfalls exist in various aspects, including rectal anatomy, MRI protocols and strategies for artifact resolution, as well as in T- and N-staging, all of which limit the diagnostic value of MRI. This narrative and pictorial review offers a comprehensive overview of factors influencing primary staging of rectal cancer and the role of MRI in assessing them. It highlights the significance of the circumferential resection margin and its relationship with the mesorectal fascia, as well as the prognostic role of extramural venous invasion and tumor deposits. Special attention is given to tumors of the lower rectum due to their complex anatomy and the challenges they pose in MRI staging. The review also addresses current controversies in rectal cancer staging and the need for personalized risk stratification. In summary, this review provides valuable insights into the role of MRI in the primary staging of rectal cancer, emphasizing key aspects for accurate assessment to enhance patient outcomes.

Operative trends following the adoption of nonoperative management of rectal cancer

BACKGROUND

Differentiating clinical near-complete and complete responses (cCR) after neoadjuvant therapy (NT) is challenging in rectal cancer patients. We hypothesized that magnetic resonance imaging staging limitations for low rectal cancers may increase the proportion of abdominoperineal resection (APR) with permanent colostomy for those without a cCR.

METHODS

Single institution retrospective analysis of rectal cancer cases before and after adoption of nonoperative "watch and wait" (W&W) pathway. APR as a percentage of rectal resections was the primary outcome.

RESULTS

There were 76 total mesorectal excisions (TME) in the pre-W&W group and 98 in the post-W&W group. NT was significantly more common in the post-W&W group. There was no significant difference in the APR primary outcome (pre-W&W APR 33.3% vs. post-W&W APR 26.5%, p = 0.482). APR patients had fewer complete TME grades (69.2% vs. 46.2%) and more pathologic complete responses (0% vs. 26.9%) in the post-W&W period. The cCR rate for patients with nonoperative management was 51.4% (n = 37) and 13.5% (n = 5) had regrowths, all of whom underwent salvage surgery.

CONCLUSION

APR for those without a cCR to NT has not increased in the nonoperative management era. Balancing the pathologic complete response rate may require restaging some patients with clinical near-complete responses.

Interdisciplinary Spanish consensus on a watch-and-wait approach for rectal cancer

Watch-and-wait has emerged as a new strategy for the management of rectal cancer when a complete clinical response is achieved after neoadjuvant therapy. In an attempt to standardize this new clinical approach, initiated by the Spanish Cooperative Group for the Treatment of Digestive Tumors (TTD), and with the participation of the Spanish Association of Coloproctology (AECP), the Spanish Society of Pathology (SEAP), the Spanish Society of Gastrointestinal Endoscopy (SEED), the Spanish Society of Radiation Oncology (SEOR), and the Spanish Society of Medical Radiology (SERAM), we present herein a consensus on a watch-and-wait approach for the management of rectal cancer. We have focused on patient selection, the treatment schemes evaluated, the optimal timing for evaluating the clinical complete response, the oncologic outcomes after the implementation of this strategy, and a protocol for surveillance of these patients.

Should the Baseline MRI Staging Criteria Differentiate Between Mucinous and Classical Rectal Adenocarcinoma?

RATIONALE AND OBJECTIVES

To compare baseline MR imaging features for pre-treatment staging between rectal mucinous adenocarcinoma (RMAC) and rectal classical adenocarcinoma (RCAC), and to investigate whether the subtype of mucinous carcinoma influences MRI evaluation criteria and high-risk tumors identifying.

METHODS

A total of 306 patients who underwent surgical rectal cancer resection were retrospectively reviewed in the study. MR imaging parameters of the primary tumor and lymph nodes (LNs) were compared between two subtypes. Logistic regression and receiver operating characteristic analyses were performed to test significant associations between LN imaging parameters and malignant LN status in RMAC and RCAC, respectively.

RESULTS

The length of mucinous tumors was larger than RCAC tumors in pT3 and pT4 stage. For pN0 patients, the long and short diameters of the largest LN on MRI were more likely to be larger in RCAC than RMAC. For pN+ patients, the proportion of LNs exhibiting internal heterogeneity in RMAC was obviously greater than that in RCAC. The best cut-off value of the largest short diameter of malignant LNs was 6.05 mm for RMAC and 8.05 mm for RCAC. And the highest AUC for predicting LNs metastases based on the largest short diameter was 0.794 for RMAC using 6 mm size cut-off, and 0.667 for RCAC using 8 mm cut-off.

CONCLUSION

The imaging features that were associated with LN metastases were different between RMAC and RCAC, and different size criteria of LNs was suggested to distinguish high-risk tumors. Clinicians should stay vigilant of LN status and take histologic subtypes into consideration before assigning clinical strategies.