Normal Anatomy of Colon explained with Video and ImagesVideo Transcript: This pouch-like structure, present at the beginning of the colon is called as caecum. This part, present on the right side of the abdomen, extending upwards from the caecum is called an ascending colon. The longest part of the colon, that extends from the right to the left side of the abdomen, is called as transverse colon. And this part, which extends downwards from transverse colon, on the left side of the abdomen, is called as descending colon. And this last part, which connects colon to the rectum and anal canal is called as sigmoid colon. These are the loops of the small intestine that occupy the central part of the abdomen. This is the cross-section from the wall of the colon, with the upper part being inside and lower part being outside of the wall. The innermost layer is epithelium, followed by this layer called as lamina propria. Outer to which lies muscularis mucosa. Then comes the submucosa. Outer to which lies the muscularis propria which is followed by a layer of pericolorectal tissue. On the outermost aspect, lies this layer which is called as serosa.
What is the TNM Staging for Colon Cancer?Video Transcript: Now we will discuss the T-staging for colon cancer. Tis is the disease which is limited to the epithelium. If it infiltrates into the lamina propria or muscularis mucosa, it is called as T1a. And T1b, when it infiltrates into the submucosa. Infiltration into muscularis propria is called as T2 disease. Pericolorectal tissue infiltration is called as T3 disease. And infiltration of serosa is called as T4a. If the tumor infiltrates through the wall of colon, to involve the surrounding structures, it is called as T4b. A tumor present in almost any part of the colon may infiltrate into the small intestine. Tumor in the ascending colon may infiltrate into the right kidney. And that in the descending colon may infiltrate into the left kidney. A transverse colon tumor may extend to involve pancreas. And may even extend to involve the stomach. Now we will discuss the N staging or the nodal staging for colon cancer. In this figure, you can see the draining lymph nodes for the colon. It can be called as N1 or N2, depending upon the number of lymph nodes involved. Lastly, we will discuss the M-staging or the metastatic staging of the colon cancer. As you can see in the figure, the venous drainage from most of the part of colon, ultimately pass through the liver. So liver is the most common site for the distant spread of the tumor from colon. As you can see in this figure, the tumor in the right side of colon has spread to the liver. In this figure, a left sided tumor has spread to the liver. Due to the direction of vascular drainage, after liver, lungs are the second most common organs involved by metastasis. This figure shows the spread of colon cancer to both the lungs, in form of multiple nodular deposits. And sometimes, both lungs and liver maybe involved in the metastatic spread of the disease, as we can see in this figure. The tumor may also spread to the peritoneum, in form of peritoneal deposits. It may rarely spread to one or both the ovaries. Very rarely, the tumor may also spread to the brain or bones. TNM is the most commonly used staging system for colorectal cancer. It uses mainly 3 parameters: “T” stands for “Tumor”; “N” for “Lymph Nodes”; and “M” for “Metastasis”. Numbers and/or letters after T (0, is, 1, 2, 3, and 4), N (0, 1, and 2), and M (0 and 1) provide more details about each of these parameters. Once T, N, and M are determined, it is used to assign an overall stage (from 0 to IV).
T STAGINGTis – Pre-cancerous or cancer cells present only in the superficial layer (epithelium) of colorectal mucosa T1 – Cancer extends to the lamina propria T2 – Cancer extends to the muscular layer (muscularis propria) T3 – Cancer extends through the muscularis propria into the pericolorectal tissues T4a – Cancer has invaded up to the outermost serosa layer (or visceral peritoneum) T4b – Cancer has invaded into the adjacent structures/organs like small intestine, kidneys, pancreas, or stomach
N STAGINGN0 – Cancer has not spread to regional lymph nodes N1 – Cancer has spread to 1 to 3 nearby lymph nodes N2a – Cancer has spread to 4 to 6 nearby lymph nodes. N2b – Cancer has spread to >/=7 nearby lymph nodes.
M STAGINGM1a – Cancer has spread to one distant organ without peritoneal spread. M1b – Cancer that has spread to >/=2 distant organs without peritoneal spread. M1c – Cancer that has spread to peritoneum with or without other sites.
What are the 4 Stages of Colon Cancer?Colon cancer can be divided into 4 stages depending on the TNM classification discussed above. After determining the TNM characteristics of colon cancer, it is allotted on of the 4 stages as discussed below.
|0||Tis N0 M0|
|I||T1-2 N0 M0|
|IIA||T3 N0 M0|
|IIB||T4a N0 M0|
|IIC||T4b N0 M0|
|IIIA||T1-2 N1/1c M0|
|T1 N2a M0|
|IIIB||T3-4a N1/1c M0|
|T2-3 N2a M0|
|T1-2 N2b M0|
|IIIC||T4a N2a M0|
|T3-4a N2b M0|
|T4b N1-2 M0|
|IVA||Any T Any N M1a|
|IVB||Any T Any N M1b|
|IVC||Any T Any N M1c|
What are the Investigations for Diagnosis and Staging of Colon Cancer?Once someone is suspected to have colon cancer based on signs and symptoms, further investigations are needed to confirm the diagnosis and stage the disease. Some diagnostic techniques can accurately determine the extent of cancer invasion in the intestinal wall and spread of the disease to other body parts, which in turn help in selecting an appropriate treatment option.
Digital Rectal ExaminationDigital rectal examination can be done in which a doctor examines the rectum for an abnormality by inserting a lubricated, gloved finger via the anus. This test can provide little information about cancer within the rectum or in nearby organs. Thus, detailed investigations are required to establish the diagnosis of cancer.
Barium Enema/Double-Contrast Barium Enema (DCBE)In double contrast barium enema, a thick, viscous liquid containing barium (a heavy element that reflects x-rays) and the air is administered into the rectum and colon via the anus. Then, x-rays images are obtained for the lower abdomen where any polyps or cancer lesions are detected by the irregular barium coating. The test has relatively higher sensitivity for larger lesions and in symptomatic patients. It cannot be used to determine the extent of invasion or the spread of cancer to distant organs.
Colonoscopy is a diagnostic technique which uses a colonoscopy – a long, flexible, slender tube usually equipped with a camera, a light source, and some special instruments for biopsy or surgery. This enables the doctors to directly observe the lining of the rectum and entire colon to look for any abnormality. Biopsy samples are generally collected from abnormal areas.
Flexible sigmoidoscopyThis technique is very similar to with the only difference being the extent of the area examined during the test. Sigmoidoscopy helps in examining the distal part of the colon and the complete rectum.
Carcinoembryonic antigen (CEA)An elevated level of serum CEA may be associated with colorectal cancer, but it is of little value in detecting early-stage disease and may be false positive or false negative in some cases. This can, however, be useful in assessing the efficacy of the treatment/surgery and the progression/recurrence of the disease.
Laboratory Tests for Biopsy SamplesBiopsy samples contains a small piece of tissue, collected from the affected area with the help of a biopsy instrument. When subjected to various laboratory tests, these samples provide information about the type of cancer, the presence of specific defective genes or proteins, etc. The detected defects may then be targeted with a targeted therapy.
Imaging TestsThese tests are generally employed after the establishment of the pathological diagnosis. They help to diagnose the extent of locoregional invasion and spread of disease to the distant organs. Alternatively, these tests are employed after treatment to evaluate the treatment efficacy and to detect any signs of disease progression/recurrence. Computed tomography (CT) scan In this technique, detailed cross-sectional images of body organs are generated using x-rays, with or without a contrast medium. It can help diagnose the spread of disease to nearby/distant lymph nodes and other organs, and may also be used to guide a biopsy needle into the affected area. Positron emission tomography (PET) scan This technique uses a radioactive substance (fluorodeoxyglucose [FDG], etc) that is given via intravenous injection prior to the procedure. Cancer cells absorb larger amounts of the radioactive substance than normal cells. The areas of higher radioactivity indicate cancerous tissue on the PET scan. Thus, this technique can diagnose unsuspected spread of disease to distant body parts. It is usually combined with a CT scan (PET/CT). Magnetic resonance imaging (MRI) scan This technique provides detailed images of tissues inside the body using radio waves, a strong magnetic field, and gadolinium contrast. It can accurately diagnose the extent of invasion and spread of disease to nearby/distant body parts. Guaiac-based fecal occult blood test (gFOBT), immunochemical fecal occult blood test (iFOBT), and stool DNA test are some other useful screening techniques which might help in the diagnosis of occult disease.
Investigations for Diagnosis and Staging of Colon Cancer explained through Videohttps://youtu.be/cHO6jhu7tMU Video Transcript: CancerBro, what are the investigations required to confirm the diagnosis of colon cancer. Investigations required to confirm and stage the disease are colonoscopy, tumor markers and imaging. Colonoscopy is one of the most important investigations which is required to confirm the disease. In this, a colonoscope is passed through the rectum into the intestine, that helps in localising the site of the tumor. We can take a biopsy from the tumor for histopathological diagnosis. Also we can do an endoscopic ultrasound, to assess the depth of infiltration of tumor and involvement of adjacent structures and regional lymph nodes by the tumor. CT scan of abdomen helps us to assess the local and distant spread of the tumor to other structures. Rarely, PET CT scan may also be required. Imaging of chest with X-ray or CT scan may also be required in some cases, depending upon the symptoms. Next step is to do blood tests, to check for tumor marker. CEA is the tumor marker for colon cancer. Baseline level of CEA should be done to assess the response to treatment. So these were the investigations required to confirm the diagnosis of colon cancer, and stage the disease.
What is the Dukes Staging of Colon Cancer?Dukes A: invasion into but not through the bowel wall Dukes B: invasion through the bowel wall but not involving lymph nodes Dukes C: involvement of lymph nodes Dukes D: widespread metastases
What is the Survival according to Stage of Colorectal Cancer?Survival rates give you an idea of percentage of people that are alive 5 years after being diagnosed with colorectal cancer. It does not tell how long they live, but helps in better understanding of the treatment response. Also, what needs to be understood is that these survival rates are an average of the patients with same type and stage of cancer, that are compared to general population without the disease. It is calculated based on whether the disease is Localised, Regional or Distant.
- Cancer is limited to the bladder.
- 5 year survival 90%.
- Cancer has spread to nearby structures or lymph nodes
- 5 year survival 71%.
- Cancer has spread to distant body parts like lungs, liver or bones.
- 5 year survival 14%.
What are the Symptoms of Advanced Stage (Stage 4) Colorectal Cancer?Symptoms of advanced disease may be caused due to local involvement of nearby structures and metastasis to distant sites. Local spread may cause:
- Changes in the bowel habit- constipation or diarrhea
- Abdominal pain or discomfort
- Bloating or sense of abdominal distension
- Reddish or blackish stools (due to bleeding)
- Nausea and/or vomiting
- Ascitis or fluid collection in abdomen causing distension
- Breathlessness, cough, chest discomfort