Rectal cancer lexicon 2023 revised and updated consensus statement from the Society of Abdominal Radiology Colorectal and Anal Cancer Disease-Focused Panel

Abstract

The Society of Abdominal Radiology's Colorectal and Anal Cancer Disease-Focused Panel (DFP) first published a rectal cancer lexicon paper in 2019. Since that time, the DFP has published revised initial staging and restaging reporting templates, and a new SAR user guide to accompany the rectal MRI synoptic report (primary staging). This lexicon update summarizes interval developments, while conforming to the original lexicon 2019 format. Emphasis is placed on primary staging, treatment response, anatomic terminology, nodal staging, and the utility of specific sequences in the MRI protocol. A discussion of primary tumor staging reviews updates on tumor morphology and its clinical significance, T1 and T3 subclassifications and their clinical implications, T4a and T4b imaging findings/definitions, terminology updates on the use of MRF over CRM, and the conundrum of the external sphincter. A parallel section on treatment response reviews the clinical significance of near-complete response and introduces the lexicon of "regrowth" versus "recurrence". A review of relevant anatomy incorporates updated definitions and expert consensus of anatomic landmarks, including the NCCN's new definition of rectal upper margin and sigmoid take-off. A detailed review of nodal staging is also included, with attention to tumor location relative to the dentate line and locoregional lymph node designation, a new suggested size threshold for lateral lymph nodes and their indications for use, and imaging criteria used to differentiate tumor deposits from lymph nodes. Finally, new treatment terminologies such as organ preservation, TNT, TAMIS and watch-and-wait management are introduced. This 2023 version aims to serve as a concise set of up-to-date recommendations for radiologists, and discusses terminology, classification systems, MRI and clinical staging, and the evolving concepts in diagnosis and treatment of rectal cancer.

Keywords: Gastrointestinal tract; MRI; Oncology; Rectal adenocarcinoma; Rectal cancer.

Fig. 1

Examples of submucosal enhancing stripe (SES). A T1 tumor demonstrates intact SES throughout its base (long thin arrows). B T2 tumor with disrupted SES. The submucosal stripe is intensely enhancing at the periphery of the tumor(long thin arrows). However, it is interrupted at the central base (arrowheads), suggestive of invasion through the submucosal layer [6]

Fig. 2

Rectal cancer without and with peritoneal involvement at the anterior peritoneal reflection illustrations and MRI examples. Accurate categorization will prevent unnecessary overtreatment which has been reported to occur in greater than 10% of MRI interpretation [68]. Rectal tumor abutting the peritoneum alone should not be considered peritoneal invasion. Illustration A demonstrates tumor (blue) abutting the peritoneum without involvement. Correlating MRI T2-weighted oblique axial image (C) demonstrates high rectal tumor (orange outline) partially enveloped by peritoneum (light blue thin line) anteriorly without peritoneum thickening, with no evidence of invasion. Illustration B demonstrates nodular peritoneal thickening at the tumor base(blue) consistent with T4a. B MRI T2W axial image (D) demonstrates annular tumor (orange outline) peritoneum nodular thickening extending laterally along the anterior peritoneal reflection (red arrows).T3 tumor of the upper rectum may be considered appropriate for primary surgical resection, if otherwise low risk, with no lymph node involvement, EMVI, or mesorectal involvement [15]. T4a tumors are associated with peritoneal metastasis

Fig. 3

Peritoneal and mesorectal fascia (MRF) involvement. A Tumor of the anterior wall above the anterior peritoneal reflection involving the peritoneum. B Tumor above the anterior peritoneal reflection on the lateral wall extends anteriorly to involve the peritoneum and posteriorly to involve the MRF. C Tumor at the level of the anterior peritoneal reflection extends posterior and laterally, involving the MRF only. D Tumor below the anterior peritoneal reflection, involving the MRF anteriorly

Fig. 4

Pelvis side wall node anatomy, from upper to lower pelvis. External iliac arteries (EIA, red), external iliac vein (EIV, blue), internal iliac arteries (IIA, red), and internal iliac veins (IIV, blue), and their relationship with the external iliac lymph node region (orange), internal iliac lymph node region (green), and obturator lymph node region (yellow) are depicted. At the level of the obturator muscle, nodes medial to the internal iliac artery are internal iliac lymph nodes (region outlined in green). Lymph nodes lateral to the internal iliac artery within the yellow boundary are obturator lymph nodes [33]

Fig. 5

Pelvic nodal drainage pathway in relation to the dentate line. A For a tumor above the dentate line, the locoregional nodes (colored in gold) include the inferior mesenteric, superior rectal, internal iliac, obturator, and mesorectal nodes. Non-locoregional nodes (colored in purple) include the common iliac, external iliac, and inguinal nodes. B For a tumor below the dentate line, the locoregional nodes (colored in gold) also include the inguinal lymph nodes. Non-locoregional nodes (colored in purple) include the common iliac and external iliac nodes

Fig. 6

Criteria for suspicious lymph nodes on initial staging and restaging after neoadjuvant therapy