Colorectal cancer

Imaging for rectal cancer

From Cancer Guidelines Wiki

No systematic review has been performed for this section. The guidance below is based on current international guidelines and consensus statements considered to be relevant to Australian practice.

Background[edit source]

Patients with a new diagnosis of rectal cancer are stratified into different treatment pathways, based upon patient factors and imaging findings after each case is discussed at a multidisciplinary team meeting. Adequate local staging with high-resolution magnetic resonance imaging (MRI) requires the scan to meet internationally recognised minimum standards for spatial resolution and scan technique.[1] A suboptimal MRI scan may compromise reporting accuracy and appropriate patient management.[2]

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Overview of evidence (non-systematic literature review)[edit source]

No systematic reviews were undertaken for this topic. Practice points were based on selected evidence and guidelines. Please see Guidelines Development for more information.

Many studies, including the MERCURY trial, have demonstrated the ability of MRI to provide important prognostic information about the staging of the tumour and relationship to the mesorectal fascia (MRF) which is the potential circumferential resection margin (CRM). Using high resolution scan technique, MRI has been shown to have good accuracy in assessing the depth of T3 extension, distance of tumour to the CRM, lymph nodes assessment by morphological criteria, and the presence of extramural venous invasion (EMVI).[3][4][5][6][7]

Initial staging investigations[edit source]

High-resolution MRI[edit source]

High-resolution MRI of the rectum is the recommended primary staging imaging investigation.[8][9][10][11][1][12]

Protocol[edit source]

Coverage: L5/S1 to anal verge

The tumour and all mesorectal lymph nodes at and above the level of the tumour should be covered by high-resolution (HR) sequences.

Low tumours within 5 cm of the anal verge need imaging angled to the anal canal to assess the relationship of tumour to the levator ani muscles and anal sphincter complex.

The protocol is set out in Table 7.2.


  • Anterior saturation bands should be used. Phase L-R can be useful in the axial images to reduce breathing artefact.
  • An antiperistaltic agent (e.g hyoscine butylbromide) can be given to reduce artefact from adjacent bowel motion.
  • Patients may fast, but there is no other bowel preparation required. The use of per-rectal fluid or gel is not recommended, as it can distort the rectal wall.[1]

Table 7.2. Rectal cancer MRI protocol[edit source]
Sequence Notes
All tumours Axial large FOV To cover whole pelvis
Sagittal T2 Preferably a HR sequence (as defined in the row below)
Axial oblique T2 HR Angled to the centre of the tumour

Acquired voxel < 1.3 mm
16–18 cm FOV, 3 mm slice thickness
0.6 mm x 0.6 mm in plane resolution^

Coronal oblique T2 HR†
Optional HR T2 oblique Parallel to sacrum to cover mesorectum up to 5 cm above upper border of tumour if needed
Low tumours Coronal oblique T2 HR Angled to the anal canal
HR parameters as above
Axial oblique T2 HR†

FOV: field of view; HR: high resolution

† optional but recommended

‡ within 5cm of anal verge

^ calculated using acquired matrix measurements. Interpolated or zipped measurements do not give the required spatial resolution.

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Report[edit source]

Radiologists are expected to provide a quality report that includes all of:

  • distance from anal verge (and distance from puborectalis sling for low tumours within 5 cm of anal verge)
  • relationship to the peritoneal reflection
  • T stage of the tumour, including the distance of spread in millimetres in the axial plane if it has spread beyond the muscularis propria
  • any involvement of the peritoneal reflection or adjacent organs
  • N stage of the tumour, using morphological criteria (irregularity of border and/or internal signal heterogeneity)
  • presence or absence of extramural venous invasion (EMVI) and whether it is contiguous or non-contiguous
  • tumour involving the potential circumferential resection margin (CRM), defined as tumour within 1 mm of the mesorectal fascia or inferior total mesorectal excision (TME) plane
  • presence of involved pelvic sidewall lymph nodes outside the mesorectum.

A structured report template is preferred (see Appendix 1 for a recommended pro forma).[13] If free text is used, it should include all of the above information.

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Practice pointQuestion mark transparent.png

MRI of the rectum is the recommended staging investigation for rectal cancer.

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High-resolution sequences must be performed and must meet accepted criteria.

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Additional sequences coronal to the anal canal are required for low tumours (Table 7.2).

Practice pointQuestion mark transparent.png

Template reports are recommended, which include all of:

  • Distance from anal verge (and puborectalis sling for low tumours)
  • Relationship to the peritoneal reflection
  • T stage including spread in mm beyond muscularis
  • N stage and pelvic lymph nodes using morphological criteria
  • EMVI status
  • CRM status using 1mm as a cut-off distance.

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CT of chest, abdomen and pelvis[edit source]

CT of the chest, abdomen and pelvis should be performed as part of pre-operative staging, to assess for more distant nodal and metastatic disease. This should not replace the MRI scan of the pelvis for local staging, unless MRI is contraindicated.[8]

Protocol[edit source]

Post intravenous contrast enhanced CT chest abdomen and pelvis with oral contrast.[8][11][12]

Report[edit source]

The staging report should identify and describe:

  • the primary tumour (within limits of CT)
  • metastatic lymph nodes
  • visceral (lung, liver) and peritoneal metastatic disease.

Alternative modalities[edit source]

If a patient cannot have CT intravenous contrast, staging may be completed by either of the following:

  • non-contrast CT of the chest and ultrasound of liver
  • non-contrast CT of the chest and MRI of the liver.

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Endorectal ultrasound[edit source]

Endorectal ultrasound (ERUS) may be used to assess T1 and early T2 tumours in patients who may be appropriate for local resection techniques. However, it is not as accurate as MRI in detection of potential CRM involvement and should be performed in addition to a staging rectal MRI scan.[8][9][11]

Further staging investigations[edit source]

As per colon cancer.

Restaging MRI following neoadjuvant therapy[edit source]

The use of MRI scans following neoadjuvant treatment is limited in Australia, and is not funded by the Medicare Benefits Scheme (MBS). There is only minimal evidence that MRI scanning influences pre-treatment management plans, and it is more frequently used for assessing treatment response.[14]

Protocol[edit source]

Protocol parameters for MRI of the pelvis undertaken for the purpose of restaging are the same as for primary staging. Some groups recommend the addition of diffusion imaging,[1] and some also use post contrast sequences.

Report[edit source]

Reports should include all the same details as the staging report to give MRI (mr) findings post-neoadjuvant treatment (y) for T stage (ymrT), N stage (ymrN), EMVI status (ymrEMVI) and CRM status (ymrCRM). An additional MRI tumour regression grading system (mrTRG) score, obtained from the high-resolution T2 sequences, can be given to define the amount of residual tumour compared to fibrosis to stratify patient response (Table 7.3).[15]

Table 7.3. Definition of MRI tumour regression grading system scores[edit source]
Score Definition
mrTRG1 No/minimal fibrosis visible (tiny linear scar) and no tumour signal
mrTRG2 Dense fibrotic scar (low signal) but no tumour signal
mrTRG3 Fibrosis predominates but obvious measureable areas of tumour signal visible
mrTRG4 Tumour signal predominates with little / minimal fibrosis
mrTRG5 Tumour signal only – no fibrosis. Includes tumour progression

Source: Patel et al 2012[15]

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Surveillance imaging[edit source]

As per colon cancer.

Staging of recurrence[edit source]

Detection or suspicion of recurrence on clinical follow up, colonoscopy or CT may be further evaluated with PET-CT to assess local and systemic spread. If distant disease is absent or resectable and pelvic exenteration is planned for local recurrence, a pelvic MRI should be performed to define the extent of local disease.

Next section: rectal MRI cancer report

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References[edit source]

  1. 1.0 1.1 1.2 1.3 Spada C, Stoker J, Alarcon O, Barbaro F, Bellini D, Bretthauer M, et al. Clinical indications for computed tomographic colonography: European Society of Gastrointestinal Endoscopy (ESGE) and European Society of Gastrointestinal and Abdominal Radiology (ESGAR) Guideline. Eur Radiol 2015 Feb;25(2):331-45 Available from:
  2. Suzuki C, Torkzad MR, Tanaka S, Palmer G, Lindholm J, Holm T, et al. The importance of rectal cancer MRI protocols on interpretation accuracy. World J Surg Oncol 2008 Aug 20;6:89 Available from:
  3. Beets-Tan RG. MRI in rectal cancer: the T stage and circumferential resection margin. Colorectal Dis 2003 Sep;5(5):392-5 Available from:
  4. Brown G, Richards CJ, Bourne MW, Newcombe RG, Radcliffe AG, Dallimore NS, et al. Morphologic predictors of lymph node status in rectal cancer with use of high-spatial-resolution MR imaging with histopathologic comparison. Radiology 2003 May;227(2):371-7 Available from:
  5. MERCURY Study Group.. Diagnostic accuracy of preoperative magnetic resonance imaging in predicting curative resection of rectal cancer: prospective observational study. BMJ 2006 Oct 14;333(7572):779 Available from:
  6. MERCURY Study Group.. Extramural depth of tumor invasion at thin-section MR in patients with rectal cancer: results of the MERCURY study. Radiology 2007 Apr;243(1):132-9 Available from:
  7. Koh DM, Smith NJ, Swift RI, Brown G. The Relationship Between MR Demonstration of Extramural Venous Invasion and Nodal Disease in Rectal Cancer. Clin Med Oncol 2008;2:267-73 Available from:
  8. 8.0 8.1 8.2 8.3 National Institute for Health and Care Excellence. Colorectal cancer: The Diagnosis and Management of colorectal cancer. United Kingdom: National Institute for Health and Care Excellence; 2014.
  9. 9.0 9.1 New Zealand Guidelines Group. Colorectal cancer: Management of Early Colorectal Cancer. Wellington: Ministry of Health; 2011.
  10. 10.0 10.1 National Comprehensive Cancer Network. NCCN Guidelines: Colon Cancer. National Comprehensive Cancer Network; 2016.
  11. 11.0 11.1 11.2 Radiologists TRCo. Recommendations for cross-sectional imaging in cancer management - colon, rectum and anal cancer. Radiologists TRCo; 2014.
  12. 12.0 12.1 National Comprehensive Cancer Network. NCCN Guidelines for Rectal Cancer Version 2.; 2016 Available from:
  13. Goergen, S. Radiology Written Report Guideline. Sydney: The Royal Australian and New Zealand College of Radiologists; 2011 [cited 2016 Dec 24] Available from:
  14. McBrearty A, McCallion K, Moorehead RJ, McAllister I, Mulholland K, Gilliland R, et al. Re-Staging Following Long-Course Chemoradiotherapy For Rectal Cancer: Does It Influence Management? Ulster Med J 2016 Sep;85(3):178-181 Available from:
  15. 15.0 15.1 Patel UB, Brown G, Rutten H, West N, Sebag-Montefiore D, Glynne-Jones R, et al. Comparison of magnetic resonance imaging and histopathological response to chemoradiotherapy in locally advanced rectal cancer. Ann Surg Oncol 2012 Sep;19(9):2842-52 Available from:

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