Perry J. Pickhardt, MD; Pamela A. Nugent, MD; Pauline A. Mysliwiec, MD, MPH; J. Richard Choi, ScD, MD; William R. Schindler, DO
Disclaimer: The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.S. Navy, U.S. Army, or U.S. Department of Defense.
Acknowledgment: The authors thank Cara Olsen, Biostatistics Consulting Center, Uniformed Services University of the Health Sciences, Bethesda, Maryland, for her statistical analysis support.
Grant Support: By the U.S. Department of Defense Advances in Medical Practice (AMP) funds.
Potential Financial Conflicts of Interest:Patents pending: P.J. Pickhardt (Naval Medical Research Center).
Requests for Single Reprints: Perry J. Pickhardt, MD, Department of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Avenue, Madison, WI 53792-3252; e-mail, email@example.com.
Current Author Addresses: Dr. Pickhardt: Department of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Avenue, Madison, WI 53792-3252.
Dr. Nugent: Department of Radiology, National Naval Medical Center, 8901 Wisconsin Avenue, Bethesda, MD 20889-5600.
Dr. Mysliwiec: Division of Gastroenterology and Hepatology, Department of Internal Medicine, University of California, Davis, Medical Center, 4150 V Street, Suite 3500, Sacramento, CA 95817.
Dr. Choi: Department of Radiology, Walter Reed Army Medical Center, 6900 Georgia Ave NW, Washington, DC 20307.
Dr. Schindler: Department of Gastroenterology, Naval Medical Center San Diego, 34800 Bob Wilson Drive, San Diego, CA 92134.
Author Contributions: Conception and design: P.J. Pickhardt, P.A. Mysliwiec, J.R. Choi, W.R. Schindler.
Analysis and interpretation of the data: P.J. Pickhardt, P.A. Mysliwiec, J.R. Choi, W.R. Schindler.
Drafting of the article: P.J. Pickhardt, P.A. Mysliwiec, J.R. Choi.
Critical revision of the article for important intellectual content: P.J. Pickhardt, P.A. Mysliwiec.
Final approval of the article: P.J. Pickhardt, P.A. Nugent, P.A. Mysliwiec, J.R. Choi, W.R. Schindler.
Provision of study materials or patients: P.J. Pickhardt, P.A. Nugent, J.R. Choi, W.R. Schindler.
Obtaining of funding: P.J. Pickhardt, J.R. Choi.
Administrative, technical, or logistic support: P.J. Pickhardt, P.A. Nugent, J.R. Choi, W.R. Schindler.
Collection and assembly of data: P.J. Pickhardt, P.A. Nugent, P.A. Mysliwiec, J.R. Choi, W.R. Schindler.
Previous estimates of the adenoma miss rate with optical colonoscopy (OC) are hindered by the use of OC as its own reference standard.
To evaluate the frequency and characteristics of colorectal neoplasms that are missed prospectively on OC by using virtual colonoscopy (VC) as a separate reference standard.
Prospective, multicenter screening trial.
3 medical centers.
1233 asymptomatic adults who underwent same-day VC and OC.
Colorectal neoplasms (adenomatous polyps) missed at OC before VC results were unblinded.
Fourteen (93.3%) of 15 nonrectal neoplasms were located on a fold; 10 (71.4%) of these were located on the backside of a fold. Five (83.3%) of 6 rectal lesions were located within 10 cm of the anal verge.
Estimation of the OC miss rate depended on polyp detection on both VC and second-look OC and therefore underestimates the true OC miss rate, particularly for smaller polyps.
Most clinically significant adenomas missed prospectively on OC are located behind a fold or near the anal verge. The 12% OC miss rate for large adenomas (≥ 10 mm) when state-of-the-art 3-dimensional VC is used as a separate reference standard is increased from the previous 0% to 6% estimates derived by using OC as its own reference standard.
How often does colonoscopy miss adenomas?
During a multicenter screening trial, experienced colonoscopists performed same-day optical (OC) and virtual colonoscopy (VC) on 1233 asymptomatic adults. Optical colonoscopy performed without knowledge of the VC findings missed 55 of 511 polyps; 21 of these polyps were adenomas measuring 6 mm or greater. Adenomas missed by OC were usually on the proximal side of a fold or near the anal verge. Virtual colonoscopy missed 14% of the adenomas that measured 6 mm or greater that were de-tected by OC.
Neither OC nor VC is a perfect test: Each misses 10% to 14% of adenomas that measure 6 mm or greater.
Table. Characteristics of Neoplasms Missed at Prospective Colonoscopic Evaluation
Unblinded 6-mm tubular adenoma located on the proximal aspect of a fold at the hepatic flexure.Left.Right.
Unblinded 6-mm tubular adenoma located at the inner aspect of a sigmoid flexure.Left.lineRight.arrowcircle
Unblinded 7-mm tubular adenoma located in the distal rectum.Left.arrowarrowheadRight.arrow
Unblinded 11-mm malignant polyp located near the hepatic flexure.Left.Right.
Potential colonoscopic “blind spots.”
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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, et al. 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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