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Using Virtual Colonoscopy for Colon Cancer Screening

August 31, 2009
Written by: , Filed in: Abdominal Imaging
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Colon cancer is a significant health problem in the United States, and globally. In the US, it is the third most frequent cancer and the second most frequent cause of cancer death.

Unfortunately, by the time patients present and are symptomatic, the disease has already spread. Fortunately, when detected early, colon cancer is highly treatable.

In order to impact morbidity and mortality due to colon cancer (also referred to as colorectal cancer), we need to implement screening for colon cancer on a widespread basis.

Colon cancer is a great cancer to screen for because, unlike other cancers, we actually have the opportunity to detect precancerous lesions and prevent the disease from advancing, since most colon cancers arise from precancerous adenomatous polyps.

Colon cancer screening relies on detecting the precancerous polyps, and one of the main problems with screening is that polyps are very common. It is estimated that more than half of patients over the age of 50 have some polyps. Not all polyps are adenomatous.

A small number of adenomatous polyps can go on to become cancer, but it can take between 10 and 15 years for an adenoma to become a carcinoma. Many patients have polyps so, in order to screen for colon cancer, you need to screen everybody for colon cancer, and particularly people who have a family history of colon cancer or unusual abdominal or bowel symptoms.

We have a variety of screening choices available at present, including sigmoidoscopy, virtual colonoscopy and conventional colonoscopy.

The most definitive colon cancer screening procedure is conventional colonoscopy. However, it is fairly involved, requires sedation, and has risk of bleeding and perforation. The risk of death is somewhere between one and three per ten thousand, and sometimes the colonoscopist cannot reach the right colon. It is not suitable for everyone, particularly those patients who are deemed to be frail or have health concerns which would not make them an ideal candidate for such an invasive procedure.

Virtual colonoscopy uses CT to specifically image the colon and to look inside the colon to find polyps. The procedure is quick compared with more invasive colon cancer screening procedures.

Patients are in the room for about 10 minutes, and virtual colonoscopy requires no sedation. Patients do not have to take the day off work, have somebody drive them home, and there is no anesthesia risk. The scan itself only takes a matter of seconds. There is no potentially painful or even dangerous ‘poking around’ or high levels of embarrassment or other psychological issues for the patient. These advantages may encourage more people to be screened for colon cancer more regularly, for better colon cancer prevention.

Additionally, with virtual colonoscopy, you can look at the entire colon with no blind spots. Virtual colonoscopy is less invasive, and is definitely safer with less morbidity. There is a very small chance of perforation, but much less than conventional colonoscopy, and it is less expensive as well.

Related CME:
NEW FOR 2009
Abdominal & Thoracic CT/MR/US: Optimizing Practice
The University of California, San Francisco School of Medicine
Evolving technology improves radiological practice through improved image quality for anatomical interpretation and generation of functional data. The use of MDCT and fast, multi-phase imaging sequences also translates to a tremendous increase in data that requires review and handling and greater need for contrast and radiation safety awareness. This activity targets the community radiologist involved in body and cardiovascular imaging with a focus on developing an efficient workflow practice in the modern imaging environment.
Read more or order: Abdominal & Thoracic CT/MR/US: Optimizing Practice

CT/MRI of the Abdomen and Pelvis
University of California San Francisco Department of Radiology and Biomedical Imaging
Provides an updated review on the use of helical (single and multidetector-row) CT and MRI for imaging of the abdomen and pelvis. Participants will learn the current approach and uses of CT/MRI in the examination of the abdomen and pelvis including advances in abdominal MRI techniques, genitourinary applications of CT/MRI, CT colonoscopy, CT/MR angiography, and CT cholangiography.
Earn up to 12 AMA PRA Category 1 Credits™.
Abdominal Imaging CME

Correct preparation for virtual colonoscopy is key. Bowel cleansing is essential and is done with the same agents used for conventional colonoscopy. Tagging agents assist the radiologist in case there is any fluid or stool left in the colon.

Tagging can be done with Tagitol, a dilute barium agent that the patient drinks the day before while they are taking the prep. It will mix with the residual solid stool and make it look white on the CT scan so there is no way that you will confuse stool with a polyp.

Another option is Gastroview, or an iodinated agent given the night before that will tag any residual fluid so the fluid will look white. So, if there is a polyp hidden in the fluid, you will be able to see it, because the fluid will be white and the polyp will be soft-tissue density.

There might be some sensitivity in patients to the contrast agents, but in general the risk to reward ratio of performing virtual colonoscopy makes it an excellent choice for screening patients to rule out colon cancer fairly quickly and easily.

If you want to perform virtual colonoscopy in your practice, you need to be trained. You need to be trained in how to set it up, the bowel prep needed, tagging agents, and the details in performing the study. You especially need to be trained in how to read the study.

The best way is to look at real cases with colonoscopy or surgical proof. You need to have these data sets and quiz cases, and you should look at a minimum of 50 well-chosen cases that include examples of various pathology of the colon in order to discern colon cancer from other colon health issues.

In the beginning, it will take you about 45 minutes or an hour per virtual colonoscopy to screen for colon cancer. By the time you finish the 50 cases, you will be down to about a half hour, and that will get better over time as you practice reading more scans.

If the virtual colonoscopy detects polyps suggestive of colon cancer, then a full colonoscopy will need to be scheduled.

Virtual colonoscopy is not a substitute for conventional colonoscopy in cases of family history, or follow-up colon cancer screening if there have been previous findings suggestive of colon cancer, such as previous adenomatous polyps.

But is virtual colonoscopy is another valuable tool in our gastrointestinal imaging arsenal which can help detect and prevent colon cancer when still in its early stages.

Author: Karen Horton, M.D.

Related CME:
NEW FOR 2009
Abdominal & Thoracic CT/MR/US: Optimizing Practice
The University of California, San Francisco School of Medicine
Evolving technology improves radiological practice through improved image quality for anatomical interpretation and generation of functional data. The use of MDCT and fast, multi-phase imaging sequences also translates to a tremendous increase in data that requires review and handling and greater need for contrast and radiation safety awareness. This activity targets the community radiologist involved in body and cardiovascular imaging with a focus on developing an efficient workflow practice in the modern imaging environment.
Read more or order: Abdominal & Thoracic CT/MR/US: Optimizing Practice

CT/MRI of the Abdomen and Pelvis
University of California San Francisco Department of Radiology and Biomedical Imaging
Provides an updated review on the use of helical (single and multidetector-row) CT and MRI for imaging of the abdomen and pelvis. Participants will learn the current approach and uses of CT/MRI in the examination of the abdomen and pelvis including advances in abdominal MRI techniques, genitourinary applications of CT/MRI, CT colonoscopy, CT/MR angiography, and CT cholangiography.
Earn up to 12 AMA PRA Category 1 Credits™.
Abdominal Imaging CME
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