T Sammour C Lai G Roadley G Wilton AG Hill

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

CT colonography (CTc)

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

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

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

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

Subset 1 incomplete colonoscopy  CTc

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

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

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

Subset 2 CTc first  cscopy / surgery

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

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

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

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

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

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.