skip to main content
RadInfo Logo Home

Colorectal Cancer

Colorectal cancer or colorectal carcinoma is cancer of the colon and/or rectum. Your doctor may perform a colonoscopy, CT colonography (also known as virtual colonoscopy) or an air-contrast barium enema to help diagnose your condition. Your doctor also may order blood tests, an abdominal and pelvic CT, chest CT, PET/CT, pelvic MRI or an endorectal ultrasound to help assess the cancer and look for any signs of spread.

Depending on the size, extent and stage of the cancer, surgery may be required. Advanced cases may require treatment with radiation therapy such as external beam therapy (EBT). Your doctor may also prescribe chemotherapy to decrease the chance of the tumor returning elsewhere in the body.

What is colorectal carcinoma?

Colorectal carcinoma is a cancer, or malignant tumor, of the large intestine, which may affect the colon or rectum. The colon (also called the large intestine) is broken up into a few different anatomic segments and attached to your small intestine. The colon is composed of the cecum/ascending colon (on the right side of your body), the transverse colon (in the middle part of your body), the descending colon (on the left side of your body), and the sigmoid colon (in your pelvis area). The sigmoid colon connects to your rectum which is the lowest part of the large intestine that is located right above the anal canal.

Factors such as age, race, personal or family history of colon disease and diet can play a significant role in having an increased risk of developing colorectal cancer.

Many colon cancers develop over a long period of time, often arising from pre-cancerous colon polyps that gradually grow and can turn into cancer. Many early stage colon cancers do not cause any symptoms at all. Therefore, various methods of colon cancer screening are currently recommended in the hope of finding the polyp or cancer at a time when it can be removed and cured. You should talk to your physician about if and when colon cancer screening would be appropriate.

If the cancer has grown to a size where it causes symptoms, these may include:

  • Abdominal pain, cramps or gas
  • Weight loss
  • Fatigue
  • Changes in bowel movements such as diarrhea, constipation, bloating or very thin stool
  • Blood in the stool or rectal bleeding
  • Partial or complete blockage of stool/feces passage

How is colorectal cancer diagnosed and evaluated?

In order to diagnose colon cancer your doctor may order:

  • Colonoscopy: This examination uses a flexible tube with a tiny camera at the end, which is inserted through the anus into the colon. The camera captures images of the interior of the large intestine. Polyps and/or tissue samples may be removed and evaluated to determine whether they are cancerous.
  • CT Colonography: A small tube is inserted into the rectum and air is used to inflate the colon. Then, low radiation dose CT images of the abdomen and pelvis are obtained while you lie on your back and then stomach. You may also be asked to lie on your side. Specially trained radiologists will usually interpret this exam using software designed for CT colonography. This exam can also detect polyps and masses. If abnormalities are found, you will typically need to get a regular colonoscopy.
  • Air-contrast barium enema: Also called a lower GI (gastrointestinal exam), this x-ray exam of the large intestine allows radiologists to view the colon and rectum in real-time and detect abnormal growths. This test is rarely performed for colon cancer screening in the United States as better tests are now available.

Other types of imaging exams that your doctor may order include:

  • Abdominal and Pelvic CT: This imaging procedure uses x-rays to quickly identify sources of pain or abnormalities within the gastrointestinal tract.
  • PET/CT: Positron emission tomography (PET) is a type of nuclear medicine scan that uses a small amount of radioactive material to localize areas of inflammation or cancer in the body. A PET/CT exam combines images from PET and CT scans.
  • Magnetic Resonance Imaging (MRI) of the Body: This imaging test uses a large magnet to produce detailed pictures of the internal organs. It may determine the extent of disease if the patient has been diagnosed with rectal cancer, look at the stage of the tumor or assess other organs for signs of cancer spread (metastatic disease). No radiation is involved.
  • Endorectal Ultrasound: This imaging test uses high frequency sound waves generated from a probe, which is inserted into the rectum. The sound waves create a picture of the rectal wall and surrounding tissue. No radiation is involved. This test may be used to determine the local extent of disease if the patient has been diagnosed with rectal cancer.

How is colorectal cancer treated?

Depending on the size and extent of spread of the cancer, patients may need to undergo a surgery, removing part or all of the colon, in order to remove the tumor. For some patients, an ileostomy or colostomy may be needed, which diverts bowel content into an external bag. Advanced cases may require radiation therapy treatments (usually combined with chemotherapy) prior to surgery. This is usually given as:

  • External Beam Therapy (EBT): This treatment is a form of radiation therapy done by aiming several beams of high-energy x-rays directly at a patient's tumor over the course of one to six weeks. These x-rays deliver radiation to the patient's tumor in order to destroy the cancer cells while minimizing the effects on the surrounding healthy tissues. Most common side effects are fatigue and changes in bowel movement frequency.

In many cases, chemotherapy may be used, either as a standalone treatment or in combination with radiation therapy. Chemotherapy is given to decrease the chance of the tumor returning elsewhere in the body or to decrease the amount of tumor throughout the body if all of the tumor(s) cannot be removed surgically. It is usually given over time and alternated with periods of no treatment. Side effects, such as abnormal blood-cell counts, fatigue, diarrhea, mouth sores, and a compromised immune system may occur.

Which test, procedure or treatment is best for me?

  • Staging of Colorectal Cancer
  • This page was reviewed on May 01, 2023


    Radiologist and patient consultation. View full size with caption

    Sponsored By

    Please note is not a medical facility. Please contact your physician with specific medical questions or for a referral to a radiologist or other physician. To locate a medical imaging or radiation oncology provider in your community, you can search the ACR-accredited facilities database.

    This website does not provide cost information. The costs for specific medical imaging tests, treatments and procedures may vary by geographic region. Discuss the fees associated with your prescribed procedure with your doctor, the medical facility staff and/or your insurance provider to get a better understanding of the possible charges you will incur.

    Web page review process: This Web page is reviewed regularly by a physician with expertise in the medical area presented and is further reviewed by committees from the Radiological Society of North America (RSNA) and the American College of Radiology (ACR), comprising physicians with expertise in several radiologic areas.

    Outside links: For the convenience of our users, provides links to relevant websites., RSNA and ACR are not responsible for the content contained on the web pages found at these links.