CT colonography (protocol)
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Computed tomographic (CT) colonography, also called CTC, virtual colonoscopy (VC) or CT pneumocolon, is a powerful minimally invasive technique for colorectal cancer screening.
Indications
- screening test for colorectal carcinoma
- colon evaluation after incomplete or unsuccessful
conventional colonoscopyoptical (conventional) colonoscopy - assessment of strictures
- to better evaluate the colon proximal to obstructing neoplasms detected by conventional colonoscopy
- patients with contraindications or refusing conventional colonoscopy
Technique
- patient preparation
- for optimal image quality, the colon should be clean and completely distended
- residual stool and fluid may lead to a false negative or false positive diagnosis
- residual stool may be "tagged" using oral contrast agents such as Gastrografin
- bowel distension
- optimal colonic distention is critical to technical success for proper intraluminal evaluation of the large bowel
- distension can be achieved via a pressure-regulated device with carbon dioxide (preferred) or room air
- intravenous contrast
- not necessary although it is used in some centres
- antispasmodic agent
- IV/IM hyoscine-N-butylbromide (Buscopan), an antimuscarinic drug reduces colonic motion, leading to higher quality images and reduced patient discomfort
- IV glucagon is used in some countries/institutions as a first or second-line antiperistaltic agent: its efficacy is contentious
Data acquisition and analysis
- CT scanning is ideally performed on a
multi-detectormultidetector computed tomography (MDCT) scanner in both supine and prone positions with a thin collimation - image review with the use of two-dimensional (2D) and three-dimensional (3D) displays is strongly advised for optimal evaluation
Findings
- colonic diverticulosis
- colon polyps
- colorectal carcinoma
- extrinsic lesions impressing on the colon
- extracolonic pathology
Contraindications
- acute inflammatory conditions such as acute diverticulitis, active stage of ulcerative colitis or Crohn disease
- recent abdominal or pelvic surgery
- CTC cannot be performed if a colostomy is present as there is no natural sphincter mechanism to retain the tube
- general CT contraindications e.g. pregnancy, claustrophobia, etc.
- history of severe allergy/anaphylaxis to iodinated contrast media
- patients at high risk for a gastrointestinal tumor (e.g. Lynch syndrome) may not be good candidates for CTC screening 7
Advantages
Virtual colonoscopy has several advantages over conventionaloptical colonoscopy:
- less invasive procedure, therefore complication rate lower
- takes less time
- can visualise colon beyond the obstruction or narrowing
- detects extracolonic pathology
Disadvantages
- residual faecal material can give rise to wrong interpretation
- biopsy specimen cannot be taken at the time of the procedure
- exposure to ionising radiation
See also
-<p><strong>Computed tomographic (CT) colonography</strong>, also called <strong>CTC</strong>, <strong>virtual colonoscopy</strong> (<strong>VC</strong>) or <strong>CT pneumocolon</strong>, is a powerful minimally invasive technique for <a href="/articles/colorectal-cancer-1">colorectal cancer</a> screening.</p><h4>Indications</h4><ul>- +<p><strong>Computed tomographic (CT) colonography</strong>, also called <strong>CTC</strong>, <strong>virtual colonoscopy</strong> (<strong>VC</strong>) or <strong>CT pneumocolon</strong>, is a powerful minimally invasive technique for <a href="/articles/colorectal-cancer-1">colorectal cancer</a> screening. </p><h4>Indications</h4><ul>
-<li>colon evaluation after incomplete or unsuccessful conventional colonoscopy</li>- +<li>colon evaluation after incomplete or unsuccessful optical (conventional) colonoscopy</li>
-<li>CT scanning is ideally performed on a multi-detector computed tomography (MDCT) scanner in both supine and prone positions with a thin collimation</li>- +<li>CT scanning is ideally performed on a multidetector computed tomography (MDCT) scanner in both supine and prone positions with a thin collimation</li>
-<li><a href="/articles/colorectal-carcinoma">colorectal carcinoma</a></li>-<li>extrinsic lesions impressing the colon</li>- +<li><a href="/articles/colorectal-cancer-1">colorectal carcinoma</a></li>
- +<li>extrinsic lesions impressing on the colon</li>
-<li>history of severe allergy / <a href="/articles/anaphylaxis">anaphylaxis</a> to iodinated contrast media</li>- +<li>history of severe allergy/<a href="/articles/anaphylaxis">anaphylaxis</a> to <a href="/articles/iodinated-contrast-media-1">iodinated contrast media</a>
- +</li>
-</ul><h4>Advantages</h4><p>Virtual colonoscopy has several advantages over conventional colonoscopy:</p><ul>- +</ul><h4>Advantages</h4><p>Virtual colonoscopy has several advantages over optical colonoscopy:</p><ul>
-<li>exposure to ionising radiation</li>- +<li>exposure to <a href="/articles/ionising-radiation">ionising radiation</a>
- +</li>
Updates to Synonym Attributes
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CTC (CT colon)
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