Current controversies in TNM for the radiological staging of rectal cancer and how to deal with them: results of a global online survey and multidisciplinary expert consensus

Abstract

Objectives: To identify the main problem areas in the applicability of the current TNM staging system (8^th ed.) for the radiological staging and reporting of rectal cancer and provide practice recommendations on how to handle them.

Methods: A global case-based online survey was conducted including 41 image-based rectal cancer cases focusing on various items included in the TNM system. Cases reaching < 80% agreement among survey respondents were identified as problem areas and discussed among an international expert panel, including 5 radiologists, 6 colorectal surgeons, 4 radiation oncologists, and 3 pathologists.

Results: Three hundred twenty-one respondents (from 32 countries) completed the survey. Sixteen problem areas were identified, related to cT staging in low-rectal cancers, definitions for cT4b and cM1a disease, definitions for mesorectal fascia (MRF) involvement, evaluation of lymph nodes versus tumor deposits, and staging of lateral lymph nodes. The expert panel recommended strategies on how to handle these, including advice on cT-stage categorization in case of involvement of different layers of the anal canal, specifications on which structures to include in the definition of cT4b disease, how to define MRF involvement by the primary tumor and other tumor-bearing structures, how to differentiate and report lymph nodes and tumor deposits on MRI, and how to anatomically localize and stage lateral lymph nodes.

Conclusions: The recommendations derived from this global survey and expert panel discussion may serve as a practice guide and support tool for radiologists (and other clinicians) involved in the staging of rectal cancer and may contribute to improved consistency in radiological staging and reporting.

Key points: • Via a case-based online survey (incl. 321 respondents from 32 countries), we identified 16 problem areas related to the applicability of the TNM staging system for the radiological staging and reporting of rectal cancer. • A multidisciplinary panel of experts recommended strategies on how to handle these problem areas, including advice on cT-stage categorization in case of involvement of different layers of the anal canal, specifications on which structures to include in the definition of cT4b disease, how to define mesorectal fascia involvement by the primary tumor and other tumor-bearing structures, how to differentiate and report lymph nodes and tumor deposits on MRI, and how to anatomically localize and stage lateral lymph nodes. • These recommendations may serve as a practice guide and support tool for radiologists (and other clinicians) involved in the staging of rectal cancer and may contribute to improved consistency in radiological staging and reporting.

Keywords: Consensus; Guideline; Magnetic resonance imaging; Neoplasm staging; Rectal neoplasms.

Fig. 1

Study outline

Fig. 2

Left: survey results showing substantial variation in assessment of cT staging in cases with various degrees of anal sphincter or pelvic floor invasion. Right: panel recommendations stating not to include the internal sphincter (IS) and intersphincteric space (ISS) in cT-stage categorization, and to consider invasion of external sphincter (ES), puborectalis, and levator ani muscles (i.e., skeletal muscles) as cT4b disease

Fig. 3

Anatomical overview of the lining of the mesorectal compartment by the MRF and peritoneum in the low, middle, and high parts of the rectum. Above the anterior peritoneal reflection, the mesorectum is lined by peritoneum anteriorly (mid) and anterolaterally (high). The remaining mesorectum is lined by the MRF. Invasion of the MRF constitutes cT3 MRF+ disease, while invasion of the peritoneum or peritoneal reflection constitutes cT4a disease. When both the peritoneum and MRF are involved, this constitutes cT4a MRF+ disease

Fig. 4

Anatomical boundaries of lateral lymph node stations (external iliac, internal iliac, obturator) on MRI. EIA = external iliac artery, EIV = external iliac vein, IIA = internal iliac artery, IIV = internal iliac vein. The border between the internal iliac and obturator compartments is defined by the lateral border of the main trunk of the internal iliac vessels (II–IV). The posterior wall of the EIV defines the border between the external iliac and obturator plus internal iliac compartments (II–VI). *The infrapiriformis foramen represents the transit point of the internal iliac vessels from the internal iliac compartment into the pudendal canal (V). This figure is largely based on a map previously published by Ogura et al JAMA Surg 2019;254: e192172 (supplement) [26]