Perry J. Pickhardt, MD; Pamela A. Nugent, MD; Pauline A. Mysliwiec, MD, MPH; J. Richard Choi, ScD, MD; William R. Schindler, DO
Flowchart shows the total number of polyps detected; the number of polyps eligible for unblinding (size ≥ 5 mm); and the number of unblinded adenomas that measured 6 mm or larger, which represent the primary study group. The 10 unblinded adenomas that measured 5 mm were excluded because of their diminutive size. VC = virtual colonoscopy.
Three-dimensional endoluminal view from virtual colonoscopy shows a sessile polyp situated on the backside of a colonic fold. Digital photograph from optical colonoscopy shows the same polyp, which was found after segmental unblinding of the virtual colonoscopy results. Note the adjacent calibrated guidewire used for polyp measurement in the study.
Three-dimensional endoluminal view from virtual colonoscopy shows a sessile polyp situated between folds. The centerline path for automated navigation is shown (line). Colon map generated from the supine computed tomography data set that shows the vantage point (arrow) for the image on the right. The polyp location (circle) is situated at the inner turn of the flexure.
Three-dimensional endoluminal view from virtual colonoscopy that simulates retroflexed view of rectal ampulla shows a subtle flat lesion (arrow) that measured 7 cm from the anal verge. Note the tip of small rectal catheter (arrowhead) that was used for air insufflation. Two-dimensional axial computed tomography image with soft tissue windowing confirms the presence of a flat rectal lesion (arrow).
Left Three-dimensional endoluminal view from virtual colonoscopy shows a large polypoid lesion on the edge of a fold. Right Digital photograph from optical colonoscopy shows the same polyp, which was found only after several attempts to reposition the instrument because of repeated slippage in this region. Invasive adenocarcinoma was confirmed at surgery.
Antegrade endoluminal view (that is, looking distally toward rectum) from virtual colonoscopy indicates the portions of colonic mucosa that were visualized during retrograde flight toward the cecum by “painting” the surface green. The unpainted regions involving the proximal aspects of colonic folds are readily evaluated during antegrade flight on virtual colonoscopy. These regions, however, are the most common sites for missed adenomas at optical colonoscopy because of its unidirectional nature.
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Walter Reed Army Medical Center
September 23, 2004
Limitations of virtual colonoscopy from the patient and gastroenterologists perspective
TO THE EDITOR: Recently, the miss rate of optical colonoscopy (OC) using virtual colonoscopy (VC) was reported in Annals as 12% for polyps Â¡Ã 10mm (1). This and the NEJM VC paper where this data originates (2) sheds a very favorable light on VC. As co-investigators in the original NEJM study and as gastroenterologists, we would like to point out aspects of this data that have not yet been advertised to cast a more balanced view of VC.
Although sensitivity and specificity of VC in the NEJM study were high, VC had a high false positive (FP) rate of 51.1% for polyps Â¡Ã 10mm per patient (47/92, 95% CI 40.4-61.7%) and a low positive predictive value (PPV) of 48.9% (45/92, 95% CI 38.3-59.6%). For polyps Â¡Ã 6mm, the FP rate was 59.3% (217/366, 95% CI 54.1-64.4%) with a PPV of 40.7% (149/366, 95% CI 35.7-45.9%) (2). Thus, if patients with polyps Â¡Ã 6mm on VC were referred for OC, 217 would have potentially received unnecessary OCÂ¡Â¯s. Similar results were recently reported by Van Gelder with VC FP rate of 41% for polyps Â¡Ã 10mm and 64% for polyps Â¡Ã 6mm (3). Incidentally, the OC miss rate in that study was 17% for polyps Â¡Ã 10mm.
Admittedly, sensitivity and specificity are more important for a screening test of a low prevalence disease. However, when the test is expensive, uncomfortable and risks high radiation exposure, the issue becomes more complex.
From the patient and the endoscopistÂ¡Â¯s perspective, the high FP rates and low PPV's are problematic, as findings on VC may represent low likelihood of true disease. Thus, patientÂ¡Â¯s anxiety about the results, and extra time spent by endoscopists may not be warranted. This high FP rate also reduces the benefit of pre-selection. These concerns have been more than academic at our institution where we have been using VC for screening.
Ultimately, despite criticism by some that VC may be an inaccurate test with sensitivity and specificity as low as 55% for polyps Â¡Ã 10mm (4), we believe it has a role for screening when performed correctly. However, results may vary with different software, protocols and technologies. Thus, when applied on a broad scale it may not be as good as originally promised, and its shortcomings may not be apparent from initial reports. VC has limitations we need to understand before we embrace it as the standard of care for routine clinical practice.
Inku Hwang, MD Roy K.H. Wong, MD Walter Reed Army Medical Center Washington, DC 20307
1. Pickhardt PJ, Nugent PA, Mysliwiec PA, Choi JR, Schindler WR. Location of adenomas missed by optical colonoscopy. Annals of Internal Medicine. 2004;141(5):352-9.
2. Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults.[see comment]. New England Journal of Medicine. 2003;349(23):2191- 200.
3. Van Gelder RE, Nio CY, Florie J, et al. Computed tomographic colonography compared with colonography in patients at increased risk for colorectal cancerl. Gastroenterology. 2004;127(1):41-8.
4. Cotton PB, Durkalski VL, Pineau BC, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA. 2004;291(14):1713 -9.
Pickhardt PJ, Nugent PA, Mysliwiec PA, Choi JR, Schindler WR. Location of Adenomas Missed by Optical Colonoscopy. Ann Intern Med. 2004;141:352-359. doi: 10.7326/0003-4819-141-5-200409070-00009
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Published: Ann Intern Med. 2004;141(5):352-359.
Colonoscopy/Sigmoidoscopy, Gastroenterology/Hepatology, Hematology/Oncology.
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