Rectal cancer

Rectal cancers, although sharing many of the features of generic colorectal carcinoma (CRC), has different preoperative imaging assessment, with MRI rectum as the mainstay for local staging, and distinct surgical techniques (i.e. total mesorectal excision). 

Rectal cancer is generally considered a disease of the elderly, but the incidence of cases in patients under the age of 50 has been increasing. There is a slight male predilection, not seen in cancers of the rest of the large bowel.

Patients often present with altered bowel habit or rectal bleeding 3.

Similarly to the rest of the colon, the vast majority of rectal tumors are adenocarcinomas (98%), with carcinoid tumors, lymphoma, and GIST making up most of the remainder 2.

Although CT can make the diagnosis in more advanced cases, due to better soft-tissue contrast, MRI has become the fundamental imaging modality for evaluation and staging. Endorectal ultrasound also has a role in the staging, particularly for assessment and differentiation between T1 and T2 disease, but is not commonly performed by a radiologist. 

MRI may be performed for:

  • diagnosis and/or locoregional staging
    • helps evaluate which patients may benefit from neoadjuvant therapy (usually stage II and III) and for evaluating poor prognostic factors
    • helps surgical planning
  • assessment of the effectiveness/response of neoadjuvant therapy
  • monitoring for recurrence post-therapy

MRI is able not only to assess tumor stage but other important prognostic features such as local lymph node involvement and extramural venous invasion (EMVI). The key sequences are T2-weighted images parallel and perpendicular to the axis of the segment of the rectum containing the tumor. For more information, see MRI protocol for assessment of rectal cancer.

Factors to be assessed and described on MRI report:

  • T stage

    • morphology of primary tumor: annular/ulcerating/polypoidal/villous/eroding/mucinous/signet cannot be assessed
    • distance of distal edge from the anal verge
    • distance of distal edge from puborectalis sling
    • longitudinal extent
    • whether it lies above or below peritoneal reflection with approximate measurements
    • invading edge of tumor (e.g. x o'clock to y o'clock)
    • whether it is confined to or extends through muscularis propria
    • extent of extramural spread (T3 disease)
    • distance from the mesorectal fascia 
    • extramural venous invasion (EMVI)
  • N (locoregional) stage
    • size is not a reliable indicator of nodal involvement
    • irregular or spiculated margin and heterogeneous signal intensity
    • number of nodes 
    • closest node to the mesorectal fascia 
    • pelvic sidewall nodes: none/benign-looking/malignant-looking
    • evidence of peritoneal nodal involvement

Please refer to the article on Rectal cancer (staging) for further details on how to apply and report the TNM staging on imaging.

The mainstay of treatment is surgical excision, however preoperative down-staging with either radiotherapy alone (more common in Europe) or combined chemo-radiotherapy (more common in the US) is employed in T3 and/or N1 disease (see rectal cancer staging) 1.

Depending on the stage at the time of resection local recurrence rates vary from 3-32% 1 with overall good 5-year survival in T1 and T2 tumors (85-100% and 70% respectively) 1,2,5. Some focal T1 lesions are candidates for transanal endoscopic microsurgery.

The majority of local recurrences occur within 20-36 months 2,5, have positive resection margins, and have a major impact on prognosis, with 80-90% of these patients succumbing to the disease within 5 years 4.

Some authors suggest that a circumferential resection margin (CRM) of less than 1 or 2 mm (the exact cut-off is debated) confers a poorer prognosis and patients should be considered for neoadjuvant treatment 6.

Article information

rID: 7172
Synonyms or Alternate Spellings:
  • Rectal carcinoma
  • Carcinoma of the rectum
  • Cancer of the rectum
  • Rectal cancers
  • Rectal carcinomas

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Cases and figures

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  • Case 6: with recto-vesical fistula
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  • Case 7: adenocarcinoma
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  • Case 10: rectal cancer with liver mets
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