MRI of a patient with known rectal cancer . Evident on the MRI is a very large T3 stage carcinoma, highlighted in purple. The tumour has passed through the muscularis propria (the thick muscle layer), the subserosa and into the serosa (See Image 2 below), or the outermost layers of the rectum or perirectal tissue, but has not invaded any neighbouring muscles, muscle groups or organs. Findings: Moderately advanced rectal carcinoma: Stage T3.
To fully understand the MRI and stage of the rectal cancer in Image 1, it is necessary to take a brief look at the Colorectal cancer classification system. Colorectal tumours, like many other carcinomas, are staged by a grading system known as ‘TMN’ which was devised by the American Joint Committee on Cancer (AJCC) and describes the extent and spread of cancer in the body.(1) T stands for Tumour, and in Colorectal cancers describes the extent of spread through the Colonic or rectal wall. N stands for Nodal involvement and indicates the spread (or lack of) to neighbouring lymph nodes and M stands for Metastases or secondary spread to other organs around the body.
Diagram to illustrate the layers of the rectal wall.
Image 2 above can be used in conjunction with the ‘T’ staging system for Colorectal cancer as described below:-
Tx: The tumour cannot be assessed.
TO: No evidence of a primary tumour.
Tis: Carcinoma in situ in the early stages. It is confined to the mucosa and has not invaded further than the muscularis mucosa (the thin inner muscle layer on the image above).
T1: The cancer has spread into but not through the submucosa.
T2: The tumour has entered the muscularis propria, or the thick outer muscle layer but has not yet passed into the submucosa.
T3: The cancer has passed through the muscularis propria and into the subserosa/serosa, or the outermost layers of the colon or rectum.
T4: Carcinoma has extended through the wall of the colon or rectum and into neighbouring organs.
MRI of a 64 year old male. Previous sigmoidoscopy confirmed low rectal cancer. On this image there is a low rectal tumour and a visible affected perirectal node (marked in purple) and possibly another malignant side wall node adjacent to it. Later CT scan confirmed a solitary segment metastasis in the liver. Diagnosis: Low Rectal Tumour T3 N2 M1.
Image 3 nicely illustrates the TNM grading system at work. The ‘T’ for Tumour part of the grading system has been examined above so let’s take a brief look at the lymph nodes and metastatic grades below:-
Lymph Node Involvement:
Nx : Nodal involvement cannot be assessed
N0 : There is no evidence of nodal involvement
N1 : 1 to 3 regional lymph nodes are involved
N2 : Lymph node involvement of 4 or more
Mx : The presence of metastases could not be assessed
M0 : There is no clear evidence of metastases
M1 : Distant Metastases are present
It now becomes a lot easier to understand the classification system demonstrated in Image 3 above which is T3 N2 M1. As we have seen, T3 indicates the exact location of the tumour in that it is present in the serosa but has not passed through it into surrounding pelvic tissue. N2 indicates that from this sequence of MRI’s there are clearly more than 4 lymph nodes affected – the lymph nodes appeared round or of an irregular shape. M1 was discovered on a later CT scan whereby a solitary area of metastases was identified.
Colorectal cancer (also known as colon cancer, rectal cancer or bowel cancer) is a general term for cancers that develop in the colon or the rectum (parts of the large intestine).(2) Colon and rectal cancer share many features. On a worldwide scale colorectal cancer is the third most common type of cancer and accounts for about 10% of all cases. In 2012 there were 1.4 million new cases and 694,000 deaths from the disease.(3) Studies have shown that more than 80% of colorectal cancers arise from adenomatous polyps, an adenoma is a tumour that occurs in glandular tissues such as the mucosa of the small intestine and colon. Polyps are easily detectable on colonoscopy and barium enema procedures which means that screening has the potential to reduce deaths by colorectal cancer by 60%.(4)
1. Edge S, Byrd DR, Carducci, et al. (eds.) AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer; 2009.
2. ‘General Information About Colon Cancer’. NCI. 2014-05-12. Retrieved 29 June 2014.
3. 2 World Cancer Report 2014. World Health Organization. 2014. pp. Chapter
4. He J, Efron, JE (2011). “Screening for colorectal cancer”. Advances in surgery 45: 31–44. doi:10.1016/j.yasu.2011.03.006. PMID 21954677