Indications.
1/ CTC as total colon examination technique.
1/ CTC as screening technique.
* RESULTS
The need for a total colon examination.
Older and even more recent reports show sufficient data that a total colon examination is mandatory e.g. right sided disease is as important a left sided disease : Thiis-Evenson et al (Gut , 1999; 45 (6):834-839) found that more than half of the adenomas were located proximal to the sigmoid, and in nearly half of the adenomas bearing subjects examined, the adenomas were proximal to the descending colon. This indicates that examinations restricted to the sigmoid or left colon are insufficient.
We thus need a total colon examination.
Currently, conventional colonoscopy is the gold standard to obtain a total colon examination. If conventional colonoscopy is impossible because of. technical failure or obstructing lesion, than we are left with double contrast barium enema (DCBE) or virtual colonoscopy (CTC).
Johnson CD et al. published there results upon a comparison between double contrast barium enema and virtual colonoscopy for screen detection of colorectal polyps. They found CTC to be far more better than DCBE for larger as well as smaller polyps. For larger polyps (> 10mm) sensitivity was 81% for CTC vs 45% for DCBE; for smaller polyps (5-9mm), sensitivity was 72% for CTC vs 44% for DCBE. Specificity on a per patient basis was 96-99% for CTC vs 99-100% for DCBE.
So, as a conclusion, even if CTC is not as good as conventional colonoscopy, it is at least the second best technique available to obtain a total colon examination.
Therefore, there is no doubt that in case of incomplete colonoscopy due to technical failure or an obstructing lesion, CTC is the technique of choice.
The same holds true in case patients are reluctant or unwilling to undergo CTC.
For these reasons, Barish et al. (Radiol. Clin. N Am 2005;43:1049-1062) concluded that current accepted indications are
* incomplete colonoscopy because of technical failure
*incomplete colonoscopy because of an obstructing lesion
*in cases conventional colonoscopy is contra-indicated
*the frail and elderly patients
What about CTC as screening technique?
CTC is appealing as a screening technique because of its non-invasive nature.
Today three studies included a screening population:
Johnson et al. Gastroenterology 2003
Yee et al. ((Radiology 2001) :
combination of screening patients and patients with symptoms
300 pt's, including 96 in a screening setting, and 204 patients presenting with symptoms).
There was no significant difference between screening and symptomatic population:
Yee et al. |
< 5 mm |
5-9mm |
> 10 mm |
overall |
sens |
82 |
93 |
100 |
90.1 |
spec |
72 |
Johnson et al, Gastroenterology 2003
703 asymptomatic patients at higher-than-average risk for colorectal cancer
preparation: not uniform (multi centre trial); no tagging
technique: single slice and multi slice, 5mm coll
Johnson et al. |
5-9 mm |
10mm |
|
CTC sens |
double read |
54 |
63 |
CTC spec |
all |
86-95
|
95-98
|
Pickhardt PJ et al. , NEJM, Dec 2003
1233 asymptomatic adults (1201 classified as average risk for CRC)
preparation: double dosis phospho soda prep and fluid tagging
technique: MDCT: coll 1.25/2.5, reconstruction interval 1mm
Pickhardt et al. |
> 6mm |
> 8mm |
> 10mm |
CTC sens |
88.7 |
93.9 |
93.8 |
CTC spec |
79.6 |
92.2 |
96.0 |
OC sens |
92.3 |
91.5 |
87.5 |
What is mandatory to make VC an acceptable screening test ? First of all, notwithstanding the adequate results in experienced centers, there is a lack inconsistency in diagnostic performance (see results section) before widespread use can be advocated.
Improving the variability of the results is possible by standardization of the technique with accomplishment of a high quality examination in all its parts.
Substantial progress is also to be expected with CAD.
Reaching a sensitivity of > 80 % with an acceptable number of false positives will certainly improve overall performance of VC in less experienced centers.
Secondly, the cathartic preparation is still an important barrier.
Substantial progress has been achieved with the use of a reduced cathartic preparation based on fecal tagging.
Now research is performed to use a laxative-free approach for VC.
Hence it is foreseeable that laxative-free VC combined with CAD and electronic cleansing will become widely available.
Once these 2 requirements are fulfilled, the way will be open for widespread implementation of VC as a screening test for CRC.
