of clinically significant lesions
Virtual colonoscopy. Diagnosis at the Clínica
Virtual colonoscopy, also known as computed tomographic (CT) colonography, is a type of radiological examination that uses the modality of next-generation CT imaging to obtain an internal view of the entire colon.
This examination, with proper preparation conditions and next-generation equipment and experienced personnel, can help find polyps and other clinically significant lesions with a sensitivity similar to that achieved by conventional colonoscopy.
If everything proceeds normally, the test lasts approximately 15-20 minutes.
Virtual colonoscopy explores the large intestine in a minimally invasive manner, without requiring that patients be hospitalised, sedated or anaesthetised. There is also no need to insert tubes or air or subject the patients to radiation.
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We have extensive experience in conducting this type of testing.
- The procedure is indicated for the detection of polyps in the colon as part of an early detection programme for colorectal cancer and precursor lesions.
- Candidates for this procedure are patients at high clinical risk whose medical condition represents an increased risk of experiencing complications during the implementation of conventional colonoscopy. For example, patients undergoing anticoagulant therapy, those with breathing difficulties and the elderly.
- The procedure is also indicated when colonoscopy cannot reach the entire length during the examination due to stretching of the intestine or obstruction for some reason, for example by a tumour or prior inflammatory process.
- Preoperative staging of colorectal cancer.
After cleansing the intestine with appropriate medication in the days prior to the examination, the patient arrives at the radiology laboratory, where the CT laboratory is located, and lies down on the examination table on their left side.
Prior insufflation of the colon with air is necessary to distend the intestine to eliminate any folding or wrinkles in the walls that could hide potential polyps or lesions.
The procedure is performed by means of a very fine, flexible enema cannula, which is inserted into the rectum and enables manual (or automatic in some cases) insufflation within the colon.
Once the colon has been filled with air, the patient is placed faced down and the clinician proceeds with the examination. The patient will need to hold their breath while the CT table is in motion and the images are acquired.
A second pass through the machine is performed with the patient facing upwards to ensure that all parts of the colon are explored. Once the examination is complete, the enema cannula is withdrawn.
For best results, the colon should be free of residue.
In most cases, patients will use the same preparation for cleansing the intestine used for conventional colonoscopy (taking a liquid laxative the day before and fasting starting 24 hours from the night prior to the examination).
There are various drugs designed for this preparation (polyethylene glycol, monosodium phosphate), which are used depending on the patient’s characteristics.
A small quantity of oral contrast, known as gastrografin, is added to this preparation, which is taken with each meal in order to differentiate the residues that can remain in the lumen of the intestine, thereby helping the clinician to distinguish them from true lesions.
In general, patients who undergo CT colonography report feeling abdominal fullness or cramps during the examination after the colon is inflated.
Less than 5% of the patients report feeling intense pain.
The discomfort is transient and gradually disappears after the procedure is finished and the catheter is removed. The subsequent administration of Aerored-type drugs helps eliminate the introduced gas and reduces this discomfort.
The administration of a muscle relaxant (Buscapine) prior to the examination can improve these symptoms, although it is not routinely used.
The nursing staff in the CT control room adjoining the examination laboratory will supervise the procedure and can hear and talk with the patient at any time if necessary.
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Virtual colonoscopy is only a diagnostic procedure, which means that it cannot be used to perform a therapeutic act to solve a detected problem.
If clinically significant polyps (larger than 10 mm) are found, they will need to be removed by means of conventional colonoscopy.
The adverse effects related to CT colonography examination are rare, often of little importance and are resolved in a conservative manner when they occur.
Air enema: The insertion of air within the colon can be uncomfortable and cause swelling, but it generally does not last more than two hours.
There is a minimal risk of colon rupture (perforation) (0.03%). It is calculated that this occurs in fewer than one examination per 3500 patients.
Radiation: The risk of harmful effects is minimal given that low doses of radiation are used. The risk of radiation exposure is equivalent to or slightly greater than a conventional X-ray examination with barium enema.
This test is contraindicated for women of childbearing age who might be pregnant. Women should always tell their doctor or radiologic technologist if there is a possibility that they are pregnant.