Conventional colonoscopy

In any case, virtual gastroscopy should be considered a natural complement to a CT or MR study of the upper abdomen when a gastric disease is suspected or when a known neoplastic lesion must be staged. At the moment, mainly due to the fact that conventional gastroscopy is not invasive as colonoscopy, there is no indication to use this imaging technique as a primary method for evaluation of the gastric lumen. 

Polyps between 6 and 9 mm are defined as intermediate lesions. Most of them are eventually found to be low-grade dysplasia adenomas, less than 1% are found to be harbour invasive carcinomas and 30% are found to be hyperplastic lesions. Thus, surveillance either with conventional or virtual colonoscopy may be a reasonable option in these cases... 

Table 17.3 reports the results of the most relevant studies on CTC accuracy using conventional colonoscopy (CC) as the reference standard. Results show that the sensitivity and specificity of CTC in the detection of polyps and cancer is still lower than that of CC and that the accuracy of CTC increases with size and is highest for polyps 1 cm or larger. Therefore, CTC should not be used as a first approach... 

Ajaj W, Pelster G, Treichel U et al (2003) Dark lumen magnetic resonance colonography comparison with conventional colonoscopy for the detection of colorectal pathology. Gut 52 1738-1743... 

Akerkar GA, Yee J, Hung R et al (2001) Patient experience and preferences toward colon cancer screening a comparison of virtual colonoscopy and conventional colonoscopy. Gastrointest Endosc 54 310-315... 

Pass R, Do S, Hixson LI (1993) Fatal hyperphosphatemia following Fleet Phospo-Soda in a patient with colonic ileus. Am 1 Gastroenterol 88 929-932 Fenlon HM, Nunes DP, Schroy PC S " et al (1999) A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 341 1496-1503... 

Macari M, Bini EJ, Xue X et al (2002) Colorectal neoplasms prospective comparison of thin-section low-dose multidetector row CT colonography and conventional colonoscopy for detection. Radiology 224 383-392... 

Ristvedt SL, McFarland EG, Weinstock LB et al (2003) Patient preferences for CT colonography, conventional colonoscopy, and bowel preparation. Am J Gastroenterol... 

Schreyer AG, Rath HC, Kikinis R et al (2005b) Comparison of magnetic resonance imaging colonography with conventional colonoscopy for the assessment of intestinal inflammation in patients with inflammatory bowel disease a feasibility study. Gut 54 250-256... 

Svensson MH, Svensson E, Lasson A et al (2002) Patient acceptance of CT colonography and conventional colonoscopy prospective comparative study in patients with or suspected of having colorectal disease. Radiology... 

So a ideal 3D display mode shows the complete colonic surface without image distortion (so polyps can be recognized as such) in a time efficient way. A techniques that satisfy these three requirements has a less colonoscopy -like representation than the conventional 3D fly-through the unfolded cube display. 

Hoppe H, Quattropani C, Spreng A, Mattich J, Netzer P, Dinkel HP (2004) Virtual colon dissection with CT colonography compared with axial interpretation and conventional colonoscopy preliminary results. AJR Am J Roentgenol 182 1151-1158... 

Pickhardt PJ, Choi JR, Hwang 1 et al. (2003) CT virtual colonoscopy to screen for colorectal neosplasia in asymptomatic adults. N Engl J Med 349 2189-2198 Royster AP, Fenlon HM, Clarke PD et al. (1997) CT colonoscopy of colorectal neoplasms two-dimensional and three-dimensional virtual-reality techniques with colonoscopic coreelation. AJR 169 1237-1242 Svensson MH, Svensson E, Lasson A et al. (2002) Patient acceptance of CT colongraphy and conventional colonoscopy prospective comparative study in patients with or suspected of having colorectal disease. Radiology 222 337-345... 

The indications for CTC closely follow the indications for conventional optical colonoscopy with few exceptions. These indications include screening asymptomatic high- and average-risk patient populations, pre-operative assessment of the colon proximal to an obstructing mass, evaluation of patients with change in bowel habits, surveillance of patients post colorectal cancer surgery, and incomplete or failed colonoscopy. Patients with bleeding diathesis, contraindications to sedation, and frail and elderly patients may also be better suited for CTC than conventional colonoscopy. 

Conventional colonoscopy is also not without risk to the patient and significant morbidity and mortality has been reported (Garbay et al. 1996). The most common adverse outcome associated with conventional colonoscopy includes hemorrhage and perforation. The rate of perforation of the colon ranges from 0.2 to 0.4% after diagnostic colonoscopy, increases with polypectomy, and approximates 5% with hydrostatic balloon dilatation of colonic strictures (Zubarik et al. 1999). 

A landmark multicenter study published by Pickhardt et al. compared CT colonography and conventional colonoscopy in asymptomatic average-risk patient population. As a screening study, comparable adenoma and colorectal cancer detection rates were reported (Pickhardt et al. 2003). In... 

Several studies have shown that patients acceptance of CTC is greater than conventional colonoscopy or double contrast barium enema (Taylor et al. 2003). Development of minimal bowel prep or prep-less CTC through fecal tagging and electronic cleansing appears to be within reach, thus making a truly prep-less colorectal screening test an attractive possibility (Lefere et al. 2002). 

The indications for diagnostic CTC closely follow those for conventional colonoscopy (Rankin 1987). Rectal bleeding, heme positive stool, anemia and constipation are just a few examples. Indications for screening and diagnostic CTC are summarized in Table 2.1. 

Diagnostic CTC may be used to further evaluate findings on conventional colonoscopy. Not infrequently, diagnostic CTC is performed in patients with suspicious intramural or extra-mural masses detected on optical colonoscopy (Fig. 2.2). 

Occasionally, patients are unable to undergo conventional colonoscopy due to presence of a colonic stricture, redundant sigmoid, or contraindications to intravenous conscious sedation. Flexible sigmoidoscopy can be performed without sedation however, the majority of the colon is not evaluated. 

The assessment of colon proximal to an obstructing colonic mass has been a shortcoming of conventional colonoscopy. In the past, inter-operative palpation or post-operative colonoscopy was performed with the possibility of a second surgery required for a missed synchronous cancer or adenoma. The sensitivity of hand palpation is fairly low and intraoperative insufflation of the colon increases the risk of peritoneal contamination. 

The role of CT colonography has been evaluated specifically in this patient population. Incomplete colonoscopies secondary to post-operative strictures and rigid mesentery have been reported. In 2002, Gollub et al. reported a conventional colonoscopy failure rate of 4%-29% in post-operative or post-radiotherapy patients (Gollub et al. 2002). These patients would undergo a double contrast barium enema for complete evaluation of the colon. As discussed, CTC sensitivity for polyp detection is greater than DCBE and thus makes it a superior surveillance tool in this subset of patients. 

CTC has been shown to be superior to double contrast barium enema following incomplete conventional colonoscopy and, in fact, failed colonoscopy was the first established indication for CTC. An incomplete colonoscopy is defined as failure to intubate up to the cecum. The reported rate of failed colonoscopy ranges from 8% to as high as 35%. Patients with a history of an incomplete colonoscopy have a significantly increased risk of failing a second attempt. A multitude of reasons contribute to a failed conventional colonoscopy poor bowel... 

In patients with failed colonoscopy, Macari et al. reported CTC sensitivities of polyp detection of 87%, compared with 45% for DCBE. The specificity was also better for CTC than DCBE 98 vs 89%, respectively (Macari et al. 1999). Therefore, in this subset of patients who have failed conventional colonoscopy, CTC rather than a second attempt of conventional colonoscopy or DCBE maybe prudent. 

Ota et al. reported a study of 33 patients with Crohn s disease and compared CTC with conventional colonoscopy and DCBE in the detection of... 

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