1. T Sammour C Lai G Roadley G Wilton AG Hill

2. Introduction Colonoscopy is the gold standard
Failure rate (incomplete scope) 5 – 25%
Technical difficulty
Obstructive lesion
Barium enema  2nd line investigation
Suboptimal pickup rate
Misses up to 50% of adenomas > 10mm

3. CT colonography (CTc)

4. CT colonography (CTc) First described in 1994
Gaining acceptance as 2nd line modality for colonic visualisation
2008 meta-analysis*
More sensitive than Ba enema for lesions > 6mm
Most data from urban centers
* Sosna J et al. Critical analysis of the performance of double-contrast barium enema for detecting colorectal polyps > or = 6 mm in the era of CT colonography. Am J Roent 2008; 190(2):374-85

5. Aim
To audit the use of CT colonography in a rural NZ hospital setting

6. Timaru Hospital 131 bed hospital
South Canterbury population 54,000 ppl
CTc performed on-site
Images networked to workstation at Christchurch Radiology Group site
Read and verified by one of two radiologists

7. Methods Electronic endoscopy and radiology records Subset 1 Subset 2
April 2004 – Dec 2006
Subset 1
incomplete colonoscopy  then CTc
Subset 2
CTc first  followed by colonoscopy / surgery

8. Subset 1
incomplete colonoscopy  CTc

9. Subset 1 – incomplete cscopy
2,502 colonoscopies during study period
196 incomplete  rate of 9.6%
All of these had a CTc
Majority on same day (88.3%)
55 new lesions identified
Followed up by repeat cscopy /surgery

10. Number True Positive False 8 3 5 27 19 10 7 Total 55 28
CTc
Cscopy / surgery
Number
True
Positive
False
Polyp < 5mm 8 3 5
Polyp 6-9mm 27 19
Polyp > 10mm 10 7
Mass lesion
Total 55 28
Fix this, prefix polyps

11. Subset 1 – incomplete cscopy
Diagnostic yield =
no. of true positives / total no. of CTc done
After incomplete colonoscopy
5.6% for lesions < 10mm
8.7% for lesions > 10mm

12. Subset 2
CTc first  cscopy / surgery

13. Subset 2 – CTc then scope 568 CTc’s performed
169 had followup colonoscopy / surgery.
Normal CTc = 73
58 confirmed normal on colonoscopy
15 polyps missed by CTc (all < 5mm)
Abnormal CTc = 96
Total of 203 lesions identified
Followed up by colonoscopy / surgery 13

14. Subset 2 – CTc then scope 568 CTc’s performed
169 had followup colonoscopy / surgery.
Normal CTc = 73
58 confirmed normal on colonoscopy
15 polyps missed by CTc (all < 5mm)
Abnormal CTc = 96
Total of 203 lesions identified
Followed up by colonoscopy / surgery 14

15. Subset 2 – CTc then scope 568 CTc’s performed
169 had followup colonoscopy / surgery.
Normal CTc = 73
58 confirmed normal on colonoscopy
15 polyps missed by CTc (all < 5mm)
Abnormal CTc = 96
Total of 203 lesions identified
Followed up by colonoscopy / surgery 15

16. CTc Cscopy / surgery Number True Positive False Polyp < 5mm 59 42
Number
True
Positive
False
Polyp < 5mm 59 42 17
Polyp 6-9mm 64 29 35
Polyp > 10mm 40 37 3
Mass lesion 38 2
Total
203
146 57
Fix this

17. Subset 2 – CTc then scope For all lesions For lesions > 10mm
Sensitivity 90.7%; Specificity 50.4%
For lesions > 10mm
Sensitivity 100%; Specificity 92.1%
For cancers
Sensitivity 100%; Specificity 96.7%
But…CTc performed much better for lesions > 10mm

18. Conclusion
CT colonography is effective as a second line tool for the detection of clinically important colorectal lesions.
The advent of remote viewing of radiology images has made it possible to utilise CTc in the rural setting.