MRI of rectal cancer—relevant anatomy and staging key points

Abstract

Rectal cancer has the eighth highest cancer incidence worldwide, and it is increasing in young individuals. However, in countries with a high human development index, mortality is decreasing, which may reflect better patient management, imaging being key. We rely on imaging to establish the great majority of clinical tumour features for therapeutic decision-making, namely tumour location, depth of invasion, lymph node involvement, circumferential resection margin status and extramural venous invasion. Despite major improvements in technique resulting in better image quality, and notwithstanding the dissemination of guidelines and examples of standardised reports, rectal cancer staging is still challenging on the day-today practice, and we believe there are three reasons. First, the normal posterior pelvic compartment anatomy and variants are not common knowledge to radiologists; second, not all rectal cancers fit in review paper models, namely the very early, the very low and the mucinous; and third, the key clinical tumour features may be tricky to analyse. In this review, we discuss the normal anatomy of the rectum and posterior compartment of the pelvis, systematise all rectal cancer staging key points and elaborate on the particularities of early, low and mucinous tumours. We also include our suggested reporting templates and a discussion of its comparison to the reporting templates provided by ESGAR and SAR.

Preoperative MRI accuracy after neoadjuvant chemoradiation for locally advanced rectal cancer

“…If a vessel wall is identified, the lesion is classified as lymphovascular invasion (either lymphatic or venous) and if there are neural structures, perineural invasion is noted [13]. For the patient outcome it is important to note extranodal tumor in MRI reports, even if this might be a positive lymph node with extracapsular extension, a tumoral deposit or discontinuous EMVI [28]. In this study 18.5% of cases with initial N1c+ at MRI turned into good responders after neoadjuvant treatment.…”

MRI‐detected extramural vascular invasion (mrEMVI) as the best predictive factor to identify candidates to total neoadjuvant therapy in locally advanced rectal cancer

“…The standard study protocol, in accordance with ESGAR guidelines, 18,19 includes sagittal T2 Turbo Spin Echo (TSE) sequences (TR ≥ 4000 ms/FOV: 22-26 cm/thickness: 4 mm/Gap: 0 mm), axial and coronal T2 TSE sequences, oblique oriented with respect to the long axis of the tumor (TR ≥ 4000 ms/FOV: 20-22 cm/thickness: 3 mm/Gap: 0 mm) and diffusion weighted sequences (DWI). In selected patients, based on the presence of a diagnostic doubt or the need for further investigations, sequences were also acquired after administration of a Gadolinium-based contrast medium (Gadobutrol T1-THRIVE).…”

Re-staging and follow-up of rectal cancer patients with MR imaging when “Watch-and-Wait” is an option: a practical guide

“…Involvement of lateral pelvic sidewall lymph nodes is more likely to occur in tumours located at the level or below the peritoneal reflection, particularly if ≥ T3 [ 36 ]. The lower the location of the primary lesion, the higher the risk and in tumours < 4 cm from the anal verge, it may exceed 30% [ 36 ].…”

“…Involvement of lateral pelvic sidewall lymph nodes is more likely to occur in tumours located at the level or below the peritoneal reflection, particularly if ≥ T3 [ 36 ]. The lower the location of the primary lesion, the higher the risk and in tumours < 4 cm from the anal verge, it may exceed 30% [ 36 ]. Lymph nodes with mixed signal intensity, irregular borders or short axis ≧ 5, 7 or 8 mm (different cutoffs are considered in different studies) on staging examinations were associated with a higher likelihood of harbouring metastasis [ 37 , 38 ].…”