Virtual Colonscopy for Primary Screening

MINERVA CHIR 2005;60:139-50 A Virtual colonscopy for primaryC screening IThe future is now D P. J. PICKHARDT 1, 2 E Virtual colonoscopy (VC) is a minimally invasive ®1Department of Radiology tool that utilizes modern CT technology for col- University of Wisconsin Medical School orectal evaluation. Since its inception in 1994, VC Madison, WI, USA has continued to rapidly evolve and improve M 2Department of Radiology as a diagnostic screening tool. Early success Uniformed Services University using primary two-dimensional (2D) detection T of the Health Sciences in polyp-rich cohorts was followed by disap- Bethesda, MD, USA pointing results in low prevalence populations. Subsequent introduction of the three-dimensional (3D) endoluminal display for primaryA H polyp detection and oral contrast tagging has transformed VC into an effective primary screen- irtual colonoscopy (VC), also referred to ing tool. This state-of-the-art VC technique has Vas CT colonography, is a minimally inva- already proven to be a viable enterpriseV when sive test for the detection of colorectal polyps combined with existing optical colonoscopy and masses.G This technique, which combines practice. More widespread implementation of two-dimensionalI (2D) and three-dimensional VC screening faces multiple challenges,R but these (3D) CT displays, has been rapidly evolving are all greatly overshadowed by the immediate 1 need for increased participation in effective col- since its inception in 1994. Some of the ear- orectal screening. Given its relatively noninva- lier VC trials involving polyp-rich cohorts sive nature and the wide Eavailability of CT, VCRdemonstrated very encouraging results using holds significant potential for addressing a very a primary 2D approach to polyp detection,2, 3 important yet preventable public health con- but the initial attempts to study low preva- cern. This review will cover current VC tech- Y lence populations were rather disappointing.4- nique, compare the existing multi-center VC tri- N 6 als, discuss issues related to primary VC screen- However, subsequent improvements in VC ing, and briefly Iupdate the progress of our VC technique, particularly the use of the 3D endo- screening program. P luminal display for primary polyp detection Key words: Virtual colonoscopy - Colon diseases and oral contrast for tagging of residual fluid - Rectum diseases - Computer tomography. and stool, have transformed VC into an effective primary screening tool. These advances The opinionsM and assertions containedO herein are the pri- vate views of the authors and are not to be construed as offi- culminated in a large multi-center VC screen- cial or as reflecting the views of the Departments of the Navy ing trial that showed comparable performance or Defense. to optical colonoscopy (OC).7 Clinical imple- C mentation of this proven method for VC Address reprint requests to: P. J. Pickhardt, MD, Department screening has already been shown to be a of Radiology, University of Wisconsin Medical School, E3/311 Clinical Science Center, 600 Highland Ave, Madison, WI 53792- viable enterprise, particularly when covered by 3252. E-mail: [email protected] third-party payers and combined with an exist- Vol. 60, N. 3 MINERVA CHIRURGICA 139 PICKHARDT VIRTUAL COLONSCOPY FOR PRIMARY SCREENING TABLE I.—Potential challenges to clinical implementa- Colonic preparation tion of VC screening. Robust colonic preparation is important — Reimbursemnt of VC screening from third-party payers for accurate polyp detection.7, 10 Not only (U.S.) — Development of an acceptable diagnostic screening must the fecal matter be adequately removed, but oral contrast material shouldA be used for algorithm — Identifying the appropriate group of patients for pri- tagging any retained solid or liquid material. mary VC screening Patient preparation usually begins the day — Establishing an effective relationship with gastroente- before the examination. We have had great rology and colorectal surgery C — Establishing practice guidelines and program accredi- success with a relatively simple low-volume tation cathartic preparationI (less than 400 mL) that — Demonstrating cost effectiveness of VC screening combines 3 basic components, all of which — Dedicated training of enough radiologists and techno- are important for complete success: sodium logists phosphate for catharsis, dilute 2% barium for — Educating patients and referring physicians on the role D for VC in screening solid stool tagging, and an ionic water-solu- — Continued need for colon purgation (and development ble contrast agent for fluid opacification.10 In of non-cathartic alternatives) addition to the actual prep components, the — Issue of exposure to ionizing radiation (albeit low dose patient maintainsE a clear-liquid diet with lib- in adults) ® — Assessing the net impact of extracolonic CT findings eral hydration throughout the day. Through — Competing with other screening tools (new and old) continued testing, we have refined this prep — Flat colorectal lesions considerably compared with that used in the multi-centerM trial.7 Now, only single doses of each component Tare required the evening ing OC program.8 The dire need for increased before the examination (45 mL sodium phos- colorectal screening is quite apparent, as far phate, 250 mL 2% barium, and 60 mL gas- too many people are dying from a largely pre-A troview or gastrografin), which greatly sim- H 11 ventable disease.9 Although widespread imple- plifies the patient instructions. For patients mentation of VC screening faces multiple chal- with known or suspected renal or cardiac lenges (Table I), these are clearly overshad-V insufficiency, magnesium citrate is substitut- owed by the need for increased screening. ed forG the sodium phosphate. This review will cover the basic essentials of Less vigorous preparations for VC are cur- current VC technique, compare the 3 major rentlyI under investigation and have shown R 12 multi-center VC trials to date, address some of preliminary success in high-risk groups. The the relevant issues related to primary VC prepless designation sometimes applied to this approach is a misnomer, since a bowel screening, and provide an update on the sta-R E preparation is invariably employed. The terms tus of our VC screening program. “non-cathartic” or “minimal” prep are closer to the truth, although most would agree that Y the use of gastrografin provokes at least a VC Ntechnique mild cathartic effect. Regardless, important I trade-offs with this approach include an The basic concept behind VC isP rather sim- expected drop in accuracy in low prevalence ple: by imaging a properly cleaned and dis- populations and inability for same-day tended colon with a modern (multi-detec- polypectomy.13 Although non-cathartic preps tor) CTM scanner, clinically significant col- for VC may ultimately increase overall com- orectal polyps can be readilyO identified. pliance, I believe it should be primarily Having said that, there has been consider- reserved for patients who are unwilling to able variability in the specific techniques used undergo proper cleansing, assuming they for performing VC. ForC the purpose of this understand the consequences. Furthermore, report, emphasis will be placed on the VC this approach must first be validated in a methods that have proven most successful multi-center trial evaluating an asymptomatic to date. average-risk population. In my opinion, it is 140 MINERVA CHIRURGICA Giugno 2005 VIRTUAL COLONSCOPY FOR PRIMARY SCREENING PICKHARDT preferable to use a bowel preparation method that allows for the possibility of same-day polypectomy to avoid the need for a second prep. Our patients greatly value this one-stop shop approach to colorectal screening. A Colonic distention Gaseous distention of the colon, like prop- C er cleansing, is also critical for diagnostic success. Distention may be achieved with either I room air or carbon dioxide. The rate and degree of insufflation can be controlled by the patient, controlled by the technologist/physi- D cian, or automated. The adequacy of colonic distention prior to scanning is usually gauged on the CT scout view (Figure 1). The 2 best E (and safest) techniques for consistent colonic ® distention are patient-controlled room air insufflation and automated carbon dioxide delivery (PROTOCO2L, E-Z-EM). Perforations FigureM 1.—Scout image from CT scan performed as part of are extremely rare when these techniques VC study in 53-year-old woman undergoing colorectal are employed and are essentially unheard screening. Excellent gaseousT distention such as this is relia- bly obtained from the automated carbon dioxide delivery of in the setting of asymptomatic VC screen- system (PROTOCO2L, E-Z-EM). The sigmoid colon, howe- ing. We recently compared patient-controlled ver, often requires extra attention and its adequacy for room air insufflation versus automated car-A distention is bestH evaluated directly on the axial 2D images. bon dioxide delivery for VC screening in over 200 patients and determined that the now offer these patients same-day, unse- latter approach resulted in slightly improvedV datedG flexible sigmoidoscopy to complete colonic distention and decreased post-pro- their screening evaluation (again, a one-stop cedure discomfort (Shinners TJ, Pickhardt shopI offering). PJ, Taylor AJ, Jones DA, OlsenR CH. Colonic distention and patient comfort at screening CT colonography: prospective comparison CT scanner requirements of patient-controlled roomE air insufflationRWhile

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