MRI Evaluation of Rectal Cancer Following Preoperative Chemoradiotherapy
Introduction
MR imaging is the modality of choice in patients with newly diagnosed rectal cancer for staging and determining the initial course of treatment. Neoadjuvant/adjuvant therapy is recommended by current National Comprehensive Cancer Network (NCCN) guidelines for patients with some stage II (T3-4, node-negative disease with tumor penetration through the muscularis propria) or stage III (node-positive disease without distant metastasis) given high risk of local recurrence (Fig. 1). Additionally, tumors with poor prognostic features such as a threatened circumferential resection margin (CRM), tumors with extramural vascular invasion (EMVI), or tumors in certain anatomic locations (eg, lower third of the rectum) may benefit from neoadjuvant therapy.1
Neoadjuvant chemoradiotherapy (nCRT) for rectal cancer most commonly consists of induction chemotherapy followed by chemoradiotherapy. According to current NCCN guidelines, most patients with stage II or III rectal cancer are recommended for fluoropyrimidine-based chemotherapy and ionizing radiation to the pelvis (chemoradiotherapy) as well as chemotherapy with the total perioperative therapy course not exceeding 6 months.2, 3, 4 However, the management of rectal cancer continues to evolve and there remain several different therapy sequences depending on tumor characteristics, response to initial therapy, and various pretreatment clinical characteristics.4,5 For example, nCRT may not be indicated in patients with early T-stage low rectal tumors.6 In patients who do undergo nCRT, however, MR evaluation plays a key role in reevaluating the tumor prior to surgery.
Section snippets
Surgical Management Postneoadjuvant Therapy
MR features influence surgical planning; thus, it is necessary to understand the most common surgical approaches for rectal tumors. While local excision is typically performed for tumors confined to the rectal wall, total mesorectal excision (TME) is the standard surgical treatment for high-risk patients following nCRT. TME involves en bloc resection of the rectum and the mesorectum, the fatty tissue envelope surrounding the rectum with all blood vessels and lymphatics included.7
In tumors that
Post-Treatment MR
Repeat MR is routinely performed prior to surgery for restaging. Commonly, the tumor has undergone interval nCRT. Locally advanced rectal cancers demonstrate variable response to nCRT, with only 4%-31% of patients achieving complete remission.16 This subset of patients have improved quality of life with post-nCRT options of local excision or active surveillance.17
Following nCRT and prior to surgery, repeat high-resolution pelvic MR may be useful to assess tumor response to treatment,
Primary Tumor Size
Prior to interpretation of post-treatment MR findings, it is important to review the initial staging MR to establish the baseline appearance of the primary tumor. Changes in tumor location or tumor bulk can thus be more accurately assessed. Interval decreased tumor height has been shown to portend a better prognosis.28
Further, a decrease in tumor size correlates with tumor regression; however, it is unclear how great of a reduction in size is necessary to impact prognosis. Tumor volume
What To Report
The following features should be included in a report for the restaging of rectal cancer following nCRT:
- •
Primary tumor:
- ○
Presence or absence of remaining tumor
- ○
If present, remaining tumor length and morphologic growth pattern
- ○
Position of tumor (o'clock) and distance from tumor to anal verge and to anorectal junction
- ○
Signal characteristics of remaining tumor, including presence or absence of fibrosis and/or mucinous degeneration
- ○
yT stage and yT3 depth
- ○
- •
Lymph nodes: yN stage, addressing total number of
Conclusion
MR represents the imaging modality of choice for rectal cancer both in initial staging and for restaging following nCRT. The primary tumor location, extent, and signal characteristics must be carefully assessed. The presence of fibrosis, restricted diffusion, and enhancement characteristics are key factors in evaluating response. Additional imaging features of CRM, presence of EMVI, and lymph node involvement must also be evaluated. These imaging features play a critical role in determining
References (60)
- et al.
Total neoadjuvant therapy: A shifting paradigm in locally advanced rectal cancer management
Clin Colorectal Cancer
(2018) - et al.
Organ preservation with chemoradiotherapy plus local excision for rectal cancer: 5-year results of the GRECCAR 2 randomised trial
Lancet Gastroenterol Hepatol
(2020) Rectal cancer—the times they are a-changing
Lancet Oncol
(2012)- et al.
MRI predictive factors for tumor response in rectal cancer following neoadjuvant chemoradiation therapy – Implications for induction chemotherapy?
Int J Radiat Oncol*Biol*Phys
(2013) - et al.
Tumor volume reduction rate measured by magnetic resonance volumetry correlated with pathologic tumor response of preoperative chemoradiotherapy for rectal cancer
Int J Radiat Oncol*Biol*Phys
(2010) - et al.
MRI predicts increased eligibility for sphincter preservation after CRT in low rectal cancer
Radiother Oncol
(2020) - et al.
Predicting poor response to neoadjuvant chemoradiotherapy for locally advanced rectal cancer: Model constructed using pre-treatment MRI features of structured report template
Radiother Oncol
(2020) - et al.
High-resolution MR imaging for nodal staging in rectal cancer: Are there any criteria in addition to the size?
Eur J Radiol
(2004) - et al.
Detection of rectal cancer and response to concurrent chemoradiotherapy by proton magnetic resonance spectroscopy
Magn Reson Imaging
(2012) - et al.
Safety and feasibility of using magnetic resonance imaging criteria to identify patients with “good prognosis” rectal cancer eligible for primary surgery: the phase 2 nonrandomized QuickSilver clinical trial
JAMA Oncol
(2019)
Adoption of total neoadjuvant therapy for locally advanced rectal cancer
JAMA Oncol
Rectal cancer, version 2.2018, NCCN clinical practice guidelines in oncology
J Natl Compr Canc Netw
Nomogram for predicting the pathological tumor response from pre-treatment clinical characteristics in rectal cancer
Anticancer Res
Neoadjuvant chemoradiotherapy and tumor recurrence in patients with early T-stage cancer of the lower rectum
Ann Surg Oncol
Population-based assessment of the surgical management of locally advanced colorectal cancer
J Natl Cancer Inst
Multivisceral resection for locally advanced primary colon and rectal cancer: An analysis of prognostic factors in 201 patients
Ann Surg
Response assessment with MRI after chemoradiotherapy in rectal cancer: Current evidences
Korean J Radiol
Long-term outcomes after intersphincteric resection for low-lying rectal cancer
Ann Surg Oncol
Does extending the waiting time of low-rectal cancer surgery after neoadjuvant chemoradiation increase the perioperative complications?
Gastroenterol Res Pract
Deep pelvic surgical site infection after radiotherapy and surgery for locally advanced rectal cancer
Ann Surg Oncol
Neoadjuvant radiotherapy for rectal cancer: Meta-analysis of randomized controlled trials
Ann Surg Oncol
Timing of surgery following neoadjuvant chemoradiation in rectal cancer: A retrospective analysis from an academic medical center
J Gastrointest Oncol
A pathologic complete response to preoperative chemoradiation is associated with lower local recurrence and improved survival in rectal cancer patients treated by mesorectal excision
Dis Colon Rectum
Optimal timing of surgery after chemoradiation for advanced rectal cancer: preliminary results of a multi-center, non-randomized phase II prospective trial
Ann Surg
Influence of the interval between preoperative radiation therapy and surgery on downstaging and on the rate of sphincter-sparing surgery for rectal cancer: The Lyon R90-01 Randomized Trial
J Clin Oncol
Use of magnetic resonance imaging in rectal cancer patients: Society of Abdominal Radiology (SAR) rectal cancer disease-focused panel (DFP) recommendations 2017
Abdom Radiol
Minimizing therapy and maximizing outcomes in rectal cancer
J Clin Oncol
Restaging of rectal cancer with MR imaging after concurrent chemotherapy and radiation therapy
Radiographics
Rectal cancer: MR imaging of the mesorectal fascia and effect of chemoradiation on assessment of tumor involvement
J Magn Reson Imaging
MRI for restaging locally advanced rectal cancer: Detailed analysis of discrepancies with the pathologic reference standard
AJR Am J Roentgenol
Cited by (1)
Staging and Restaging of Rectal Cancer with MRI: A Pictorial Review
2022, Seminars in Ultrasound, CT and MRICitation Excerpt :When interpreting mucin response, it is imperative to review the pretreatment MRI tumor signal characteristics to avoid confusion with a primary mucinous rectal tumor on pretreatment MRI. Restaging primary mucinous adenocarcinomas is a unique challenge, again limited because of the similar imaging appearance of a persistent mucinous tumor and a favorable acellular mucin response (Fig 19).38,55 Features suggestive of a favorable response include decreasing signal heterogeneity and resolution of intermediate signal solid tumor components.