Flat colorectal lesions in asymptomatic adults: implications for screening with CT virtual colonoscopy

CT Colonography Reporting and Data System (C-RADS): Version 2023 Update

The CT Colonography Reporting and Data System (C-RADS) has withstood the test of time and proven to be a robust classification scheme for CT colonography (CTC) findings. C-RADS version 2023 represents an update on the scheme used for colorectal and extracolonic findings at CTC. The update provides useful insights gained since the implementation of the original system in 2005. Increased experience has demonstrated confusion on how to classify the mass-like appearance of the colon consisting of soft tissue attenuation that occurs in segments with acute or chronic diverticulitis. Therefore, the update introduces a new subcategory, C2b, specifically for mass-like diverticular strictures, which are likely benign. Additionally, the update simplifies extracolonic classification by combining E1 and E2 categories into an updated extracolonic category of E1/E2 since, irrespective of whether a finding is considered a normal variant (category E1) or an otherwise clinically unimportant finding (category E2), no additional follow-up is required. This simplifies and streamlines the classification into one category, which results in the same management recommendation.

Anorectal pitfalls in computed tomography colonography

There is a wide array of pathological lesions seen in the anorectal region with CT colonography (CTC), much of which is unique to this location. Many relatively common findings in the anorectal region are typically benign, but can be misinterpreted as malignant. There are also technique-related pitfalls that can impede accurate diagnosis of anorectal findings at CTC. Understanding common and uncommon lesions in the anorectal region as well as recognizing technical pitfalls will optimize interpretation of CTC and decrease the number of missed cancers and false positives. This review will systematically cover that they key pitfalls confronting the radiologist at CTC interpretation of the anorectal region, primarily dividing them into those related to underlying anatomy and those related to technique. Tips for how to effectively handle these potential pitfalls will also be discussed.

Positive Predictive Value for Colorectal Lesions at CT Colonography: Analysis of Factors Impacting Results in a Large Screening Cohort

OBJECTIVE. The purpose of this study is to evaluate factors affecting the positive predictive value (PPV) for detecting colorectal lesions at CT colonography (CTC), using optical colonoscopy (OC) as the reference standard for concordance. MATERIALS AND METHODS. Consecutive CTC studies from a single screening program interpreted as positive for at least one detected colorectal lesion 6 mm or larger and sent for subsequent OC were analyzed according to per-polyp and per-patient results. Univariable and multivariable analysis of multiple input factors was performed. RESULTS. Of 1650 studies (median patient age, 59.7 years; 877 men and 773 women) with 2688 total CTC-detected lesions 6 mm or larger, the overall PPVs were 88.8% (2386/2688) by polyp and 90.8% (1499/1650) by patient. The by-polyp PPV was significantly higher for polypoid (91.2%; 1793/1965) versus flat or nonpolypoid (79.4%; 459/578) lesions (p < 0.0001). Overall per-patient PPVs were 72.3% (1193/1650) for any neoplasia 6 mm or larger and 38.8% (641/1650) for advanced neoplasia. PPVs for advanced neoplasia increased by CTC Reporting and Data System category: 5.8% (45/781) for C2, 67.1% (511/762) for C3, and 79.4% (85/107) for C4. PPVs for cancer also increased by CTC Reporting and Data System category: 0% (0/781) for C2, 2.2% (17/762) for C3, and 52.3% (56/107) for C4. On multivariable regression analysis, polyp morphologic type (flat vs polypoid) and diagnostic confidence were the strongest predictors of CTC-OC concordance. CTC PPV results are somewhat underestimated because 28.8% (87/302) of CTC-OC-discordant results were categorized as likely OC false-negatives at consensus review. CONCLUSION. Concordance between CTC and OC is high for relevant colorectal polyps and masses. Unlike stool-based tests that provide only a binary positive or negative result, CTC can specify the nature of the positive findings, resulting in much greater specificity and risk stratification for patient management decisions.

Volumetric growth rates of sessile serrated adenomas/polyps observed in situ at longitudinal CT colonography

OBJECTIVE

Sessile serrated adenomas/polyps (SSA/Ps) are now recognized as potential cancer precursors, but little is known about their natural history. We assessed the in vivo growth rates of histologically proven SSA/Ps at longitudinal CT colonography (CTC) and compared results with non-advanced tubular adenomas (TAs).

METHODS

We identified a cohort of 53 patients (mean age, 54.8 ± 5.5 years; M:F, 26:27) from one center with a total of 58 SSA/Ps followed longitudinally at CTC (mean follow-up interval, 5.3 ± 1.9 years). Initial and final size measurements were determined using dedicated CTC software. Findings were compared with 141 non-advanced TAs followed at CTC (mean, 4.1 ± 2.3 years) in 113 patients (mean age, 56.8 ± 6.9 years).

RESULTS

SSA/Ps were more often flat (62% [36/58] vs. 14% [20/141], p < 0.0001) and right-sided (98% [57/58] vs. 46% [65/141], p < 0.0001) compared with TAs. Initial average diameter was greater for SSA/Ps (9.3 mm vs. 6.3 mm; p < 0.0001). Mean annual volumetric growth was + 12.7%/year for SSA/Ps vs. + 36.4%/year for TAs (p = 0.028). Using a previously defined threshold of + 20% increase in volume/year to define progression, 22% (13/58) of SSA/Ps and 41% (58/141) of TAs progressed (p = 0.014). None of the SSA/Ps had dysplasia or invasive cancer at histopathology.

CONCLUSIONS

Sessile serrated adenoma/polyps demonstrate slower growth compared with conventional non-advanced tubular adenomas, despite larger initial linear size. This less aggressive behavior may help explain the more advanced patient age for serrated pathway cancers. Furthermore, these findings could help inform future colonoscopic surveillance strategies, as current guidelines are largely restricted to expert opinion related to the absence of natural history data.

KEY POINTS

• Sessile serrated adenoma/polyps (SSA/Ps) tend to be flat, right-sided, and demonstrate slower growth compared with conventional non-advanced tubular adenomas. • This less aggressive behavior of SSA/Ps may help explain the more advanced patient age for serrated pathway cancers.

Deep learning and conditional random fields-based depth estimation and topographical reconstruction from conventional endoscopy

Colorectal cancer is the fourth leading cause of cancer deaths worldwide and the second leading cause in the United States. The risk of colorectal cancer can be mitigated by the identification and removal of premalignant lesions through optical colonoscopy. Unfortunately, conventional colonoscopy misses more than 20% of the polyps that should be removed, due in part to poor contrast of lesion topography. Imaging depth and tissue topography during a colonoscopy is difficult because of the size constraints of the endoscope and the deforming mucosa. Most existing methods make unrealistic assumptions which limits accuracy and sensitivity. In this paper, we present a method that avoids these restrictions, using a joint deep convolutional neural network-conditional random field (CNN-CRF) framework for monocular endoscopy depth estimation. Estimated depth is used to reconstruct the topography of the surface of the colon from a single image. We train the unary and pairwise potential functions of a CRF in a CNN on synthetic data, generated by developing an endoscope camera model and rendering over 200,000 images of an anatomically-realistic colon.We validate our approach with real endoscopy images from a porcine colon, transferred to a synthetic-like domain via adversarial training, with ground truth from registered computed tomography measurements. The CNN-CRF approach estimates depths with a relative error of 0.152 for synthetic endoscopy images and 0.242 for real endoscopy images. We show that the estimated depth maps can be used for reconstructing the topography of the mucosa from conventional colonoscopy images. This approach can easily be integrated into existing endoscopy systems and provides a foundation for improving computer-aided detection algorithms for detection, segmentation and classification of lesions.

Accuracy of CT Colonography for Detection of Polypoid and Nonpolypoid Neoplasia by Gastroenterologists and Radiologists: A Nationwide Multicenter Study in Japan

OBJECTIVES

The objective of this study was to assess prospectively the diagnostic accuracy of computer-assisted computed tomographic colonography (CTC) in the detection of polypoid (pedunculated or sessile) and nonpolypoid neoplasms and compare the accuracy between gastroenterologists and radiologists.

METHODS

This nationwide multicenter prospective controlled trial recruited 1,257 participants with average or high risk of colorectal cancer at 14 Japanese institutions. Participants had CTC and colonoscopy on the same day. CTC images were interpreted independently by trained gastroenterologists and radiologists. The main outcome was the accuracy of CTC in the detection of neoplasms ≥6 mm in diameter, with colonoscopy results as the reference standard. Detection sensitivities of polypoid vs. nonpolypoid lesions were also evaluated.

RESULTS

Of the 1,257 participants, 1,177 were included in the final analysis: 42 (3.6%) were at average risk of colorectal cancer, 456 (38.7%) were at elevated risk, and 679 (57.7%) had recent positive immunochemical fecal occult blood tests. The overall per-participant sensitivity, specificity, and positive and negative predictive values for neoplasms ≥6 mm in diameter were 0.90, 0.93, 0.83, and 0.96, respectively, among gastroenterologists and 0.86, 0.90, 0.76, and 0.95 among radiologists (P<0.05 for gastroenterologists vs. radiologists). The sensitivity and specificity for neoplasms ≥10 mm in diameter were 0.93 and 0.99 among gastroenterologists and 0.91 and 0.98 among radiologists (not significant for gastroenterologists vs. radiologists). The CTC interpretation time by radiologists was shorter than that by gastroenterologists (9.97 vs. 15.8 min, P<0.05). Sensitivities for pedunculated and sessile lesions exceeded those for flat elevated lesions ≥10 mm in diameter in both groups (gastroenterologists 0.95, 0.92, and 0.68; radiologists: 0.94, 0.87, and 0.61; P<0.05 for polypoid vs. nonpolypoid), although not significant (P>0.05) for gastroenterologists vs. radiologists.

CONCLUSIONS

CTC interpretation by gastroenterologists and radiologists was accurate for detection of polypoid neoplasms, but less so for nonpolypoid neoplasms. Gastroenterologists had a higher accuracy in the detection of neoplasms ≥6 mm than did radiologists, although their interpretation time was longer than that of radiologists.

Colorectal Findings at Repeat CT Colonography Screening after Initial CT Colonography Screening Negative for Polyps Larger than 5 mm

Purpose To determine the rate and types of polyps detected at repeat computed tomographic (CT) colonography screening after initial negative findings at CT colonography screening. Materials and Methods Among 5640 negative CT colonography screenings (no polyps ≥ 6 mm) performed before 2010 at one medical center, 1429 (25.3%; mean age, 61.4 years; 736 women, 693 men) patients have returned for repeat CT colonography screening (mean interval, 5.7 years ± 0.9; range, 4.5-10.7 years). Positive rates and histologic findings of initial and repeat screening were compared in this HIPAA-compliant, institutional review board-approved study. For all patients with positive findings at repeat CT colonography, the findings were directly compared against the initial CT colonography findings. Fisher exact, Pearson χ², and Student t tests were applied as indicated. Results Repeat CT colonography screening was positive for lesions 6 mm or larger in 173 (12.1%) adults (compared with 14.3% at initial CT colonography screening, P = .29). In the 173 patients, 29.5% (61 of 207) of nondiminutive polyps could be identified as diminutive at the initial CT colonography and 12.6% (26 of 207) were missed. Large polyps, advanced neoplasia (advanced adenomas and cancer), and invasive cancer were seen in 3.8% (55 of 1429), 2.8% (40 of 1429), and 0.14% (two of 1429), respectively, at follow-up, compared with 5.2% (P = .02), 3.2% (P = .52), and 0.45% (P = .17), respectively, at initial screening. Of 42 advanced lesions in 40 follow-up screenings, 33 (78.6%) were right sided and 22 (52.4%) were flat, compared with 45.4% (P < .001) and 11.3% (P < .001), respectively, at initial screening. Large right-sided serrated lesions were confirmed in 20 individuals (1.4%), compared with 0.5% (P < .001) confirmed at initial screening. Conclusion Positive rates for large polyps at repeat CT colonography screening (3.7%) were lower compared with those at initial screening (5.2%). However, more advanced right-sided lesions were detected at follow-up CT colonography, many of which were flat, serrated lesions. The cumulative findings support both the nonreporting of diminutive lesions and a 5-10-year screening interval. ^© RSNA, 2016 An earlier incorrect version of this article appeared online. This article was corrected on August 30, 2016.

CT Colonography: an update on current and future indications

Computed tomographic colonography (CTC) is a minimally invasive, patient-friendly, safe and robust colonic imaging modality. The technique is standardized and consolidated evidence from the literature shows that the diagnostic performances for the detection of colorectal cancer and large polyps are similar to colonoscopy (CS) and largely superior to alternative radiological exams, like barium enema. A clear understanding of the exact role of CTC will be beneficial to maximize the benefits and minimize the potential sources of frustration or disappointment for both referring clinicians and patients. Incomplete, failed, or unfeasible CS; investigation of elderly, and frail patients and assessment of diverticular disease are major indications supported by evidence-based data and agreed by the endoscopists. The use of CTC for symptomatic patients, colorectal cancer screening and colonic surveillance is still under debate and, thus, recommended only if CS is unfeasible or refused by patients.

Developments in Screening Tests and Strategies for Colorectal Cancer

BACKGROUND

Worldwide, colorectal cancer (CRC) is the third most common cancer in men and second most common in women. It is the fourth most common cause of cancer mortality. In the United States, CRC is the third most common cause of cancer and second most common cause of cancer mortality. Incidence and mortality rates have steadily fallen, primarily due to widespread screening.

METHODS

We conducted keyword searches on PubMed in four categories of CRC screening: stool, endoscopic, radiologic, and serum, as well as news searches in Medscape and Google News.

RESULTS

Colonoscopy is the gold standard for CRC screening and the most common method in the United States. Technological improvements continue to be made, including the promising "third-eye retroscope." Fecal occult blood remains widely used, particularly outside the United States. The first at-home screen, a fecal DNA screen, has also recently been approved. Radiological methods are effective but seldom used due to cost and other factors. Serum tests are largely experimental, although at least one is moving closer to market.

CONCLUSIONS

Colonoscopy is likely to remain the most popular screening modality for the immediate future, although its shortcomings will continue to spur innovation in a variety of modalities.

CT colonography for the detection of nonpolypoid adenomas: sensitivity assessed with restricted national CT colonography trial criteria

OBJECTIVE

The purpose of this study was to determine the prevalence of nonpolypoid adenomas and the sensitivity of CT colonography (CTC) in their detection by use of the restricted criteria of height-to-width ratio<50% and height elevation≤3 mm.

MATERIALS AND METHODS

In the National CT Colonography Trial (American College of Radiology Imaging Network protocol 6664), a cohort of 2531 participants without symptoms underwent CTC and screening colonoscopy. The CTC examinations were interpreted with both 2D and 3D techniques. Nonpolypoid adenomatous polyps identified with CTC or colonoscopy were retrospectively reviewed to determine which polyps met the restricted criteria. The prevalence of nonpolypoid adenomas and the prospective sensitivity of CTC were determined. Descriptive statistics were used to report the prevalence, size, and histologic features. The sensitivities (with 95% CIs) for nonpolypoid and polypoid lesions were compared by two-sided Z test for independent binomial proportions.

RESULTS

The retrospective review confirmed 21 nonpolypoid adenomas, yielding a prevalence of 0.83% (21 of 2531 participants). Eight (38.1%) were advanced adenomas, many (50% [4/8]) only because of large size (≥10 mm). The overall per polyp sensitivity of CTC (combined 2D and 3D interpretation) for detecting nonpolypoid adenomas≥5 mm (n=21) was 0.76; ≥6 mm (n=16), 0.75; and ≥10 mm (n=5), 0.80. These values were not statistically different from the sensitivity of detecting polypoid adenomas (p>0.37).

CONCLUSION

In this large screening population, nonpolypoid adenomas had a very low prevalence (<1%), and advanced pathologic features were uncommon in polyps<10 mm in diameter. Most nonpolypoid adenomas are technically visible at CTC. The prospective sensitivity is similar to that for polypoid adenomas when the interpretation combines both 2D and 3D review.

Colon capsule versus CT colonography in patients with incomplete colonoscopy: a prospective, comparative trial

OBJECTIVE

In case of incomplete colonoscopy, several radiologic methods have traditionally been used, but more recently, capsule endoscopy was also shown to be accurate. Aim of this study was to compare colon capsule endoscopy (CCE) and CT colonography (CTC) in a prospective cohort of patients with incomplete colonoscopy.

DESIGN

Consecutive patients with a previous incomplete colonoscopy underwent CCE and CTC followed by colonoscopy in case of positive findings on either test (polyps/mass lesions ≥6 mm). Clinical follow-up was performed in the other cases to rule out missed cancer. CTC was performed after colon capsule excretion or 10-12 h postingestion. Since the gold standard colonoscopy was performed only in positive cases, diagnostic yield and positive predictive values of CCE and CTC were used as study end-points.

RESULTS

100 patients were enrolled. CCE and CTC were able to achieve complete colonic evaluation in 98% of cases. In a per-patient analysis for polyps ≥6 mm, CCE detected 24 patients (24.5%) and CTC 12 patients (12.2%). The relative sensitivity of CCE compared to CTC was 2.0 (95% CI 1.34 to 2.98), indicating a significant increase in sensitivity for lesions ≥6 mm. Of larger polyps (≥10 mm), these values were 5.1% for CCE and 3.1% for CTC (relative sensitivity: 1.67 (95% CI 0.69 to 4.00)). Positive predictive values for polyps ≥6 mm and ≥10 mm were 96% and 85.7%, and 83.3% and 100% for CCE and CTC, respectively. No missed cancer occurred at clinical follow-up of a mean of 20 months.

CONCLUSIONS

CCE and CTC were of comparable efficacy in completing colon evaluation after incomplete colonoscopy; the overall diagnostic yield of colon capsule was superior to CTC.

TRIAL REGISTRATION NUMBER

NCT01525940.

CT colonography: accuracy, acceptance, safety and position in organised population screening

Colorectal cancer (CRC) is the second most common cancer and second most common cause of cancer-related deaths in Europe. The introduction of CRC screening programmes using stool tests and flexible sigmoidoscopy, have been shown to reduce CRC-related mortality substantially. In several European countries, population-based CRC screening programmes are ongoing or being rolled out. Stool tests like faecal occult blood testing are non-invasive and simple to perform, but are primarily designed to detect early invasive cancer. More invasive tests like colonoscopy and CT colonography (CTC) aim at accurately detecting both CRC and cancer precursors, thus providing for cancer prevention. This review focuses on the accuracy, acceptance and safety of CTC as a CRC screening technique and on the current position of CTC in organised population screening. Based on the detection characteristics and acceptability of CTC screening, it might be a viable screening test. The potential disadvantage of radiation exposure is probably overemphasised, especially with newer technology. At this time-point, it is not entirely clear whether the detection of extracolonic findings at CTC is of net benefit and is cost effective, but with responsible handling, this may be the case. Future efforts will seek to further improve the technique, refine appropriate diagnostic algorithms and study cost-effectiveness.

Contrast coating for the surface of flat polyps at CT colonography: a marker for detection

OBJECTIVES

To assess the frequency of oral contrast coating of flat polyps, which may promote detection, and influencing factors within a screening CT colonography (CTC) population.

METHODS

This was a retrospective, observational study performed at one institution. From 7,426 individuals, 123 patients with 160 flat polyps were extracted. Flat polyps were defined as plaque-like, raised at most 3 mm in height and reviewed for contrast coating. Factors including demographic variables such as age and sex, and polyp variables such as polyp size, location and histology were analysed for effect on coating.

RESULTS

Of 160 flat polyps (mean size 9.4 mm ± 3.6), 78.8 % demonstrated coating. Mean coat thickness was 1.5 mm ± 0.6; 23.8 % (n = 30) demonstrated a thin film of contrast. Large size (≥10 mm) and proximal colonic location (relative to splenic flexure) were predictive variables by univariate logistic regression [OR (odds ratio) 3.4 (CI 1.3-8.9; p = 0.011), 2.0 (CI 1.2-3.5; p = 0.011), respectively]. Adenomas (OR 0.37, CI 0.14-1.02; p = 0.054) and mucosal polyps or venous blebs (OR 0.07, CI 0.02-0.25; p < 0.001) were less likely to coat than serrated/hyperplastic lesions. Age and sex were not predictive for coating (p = 0.417, p = 0.499, respectively).

CONCLUSIONS

Surface contrast coating is common for flat polyps at CTC, promoted by large size, proximal location and serrated/hyperplastic histology. Given the difficulty in detection, recognition may aid in flat polyp identification.

KEY POINTS

• Oral contrast coats the surface of most flat colorectal polyps at CT colonography. • Large size, proximal colonic location and serrated/hyperplastic histology increase polyp coating. • Contrast coating increases diagnostic confidence for flat polyps. • Contrast coating may help in flat polyp detection at CTC.

Colorectal laterally spreading tumors by computed tomographic colonography

To date, few reports focused primarily on detecting colorectal laterally spreading tumors (LSTs) have been published. The aim of this study was to determine the visibility of LSTs on computed tomographic colonography (CTC) compared with that on colonoscopy as a standard. We retrospectively reviewed and matched data on endoscopic and CTC reports in 157 patients (161 LSTs) who received a multidetector CT scan using contrast media immediately after total colonoscopy at the National Cancer Center Hospital in Tokyo, Japan, between December 2005 and August 2010. The results of the total colonoscopy were known at the time of the CTC procedure and reading. Of the 161 LSTs detected on colonoscopy, 138 were observed and matched by CTC (86%). Of the 91 granular type LSTs (LST-Gs), 88 (97%) were observed and matched, while of the 70 non-granular type LSTs (LST-NGs), 50 (71%) were observed and matched by CTC (p < 0.0001). CTC enabled observation of 73% (22/30) of 20–29 mm, 83% (35/42) of 30–39 mm, 88% (49/56) of 40–59 mm, and 97% (32/33) of ≥60 mm tumors. The rate of observed LSTs by CTC was 86% (97% of LST-G, 71% of LST-NG) of the LSTs found during total colonoscopy.

Carpet lesions detected at CT colonography: clinical, imaging, and pathologic features

PURPOSE

To describe carpet lesions (laterally spreading tumors ≥ 3 cm) detected at computed tomographic (CT) colonography, including their clinical, imaging, and pathologic features.

MATERIALS AND METHODS

The imaging reports for 9152 consecutive adults undergoing initial CT colonography at a tertiary center were reviewed in this HIPAA-compliant, institutional review board-approved retrospective study to identify all potential carpet lesions detected at CT colonography. Carpet lesions were defined as morphologically flat, laterally spreading tumors 3 cm or larger. For those patients with neoplastic carpet lesions, CT colonography studies were analyzed to determine maximal lesion width and height, oral contrast material coating, segmental location, and computer-aided detection (CAD) findings. Demographic data and details of clinical treatment in these patients were reviewed.

RESULTS

Eighteen carpet lesions in 18 patients (0.2%; mean age, 67.1 years; eight men, 10 women) were identified and were subsequently confirmed at colonoscopy and pathologic examination among 20 potential flat masses (≥3 cm) prospectively identified at CT colonography (there were two nonneoplastic rectal false-positive findings). No additional neoplastic carpet lesions were found in the cohort undergoing colonoscopy after CT colonography and/or surgery (there were no false-negatives). Mean lesion width was 46.5 mm (range, 30-80 mm); mean lesion height was 7.9 mm (range, 4-14 mm). Surface retention of oral contrast material was noted in all 18 cases. All but two lesions were located in the distal rectosigmoid or proximal right colon. At CAD, 17 (94.4%) lesions were detected (mean, 6.2 CAD marks per lesion). Sixteen lesions (88.9%) demonstrated advanced histologic features, including a villous component (n = 11), high-grade dysplasia (n = 4), and invasive cancer (n = 5). Sixteen patients (88.9%) required surgical treatment for complete excision.

CONCLUSION

CT colonography can effectively depict carpet lesions. Common features in this series included older patient age, rectal or cecal location, surface coating with oral contrast material, multiple CAD hits, advanced yet typically benign histologic features, and surgical treatment.

Sessile serrated adenomas in the proximal colon are likely to be flat, large and occur in smokers

AIM

To examine the epidemiology and the morphology of the proximal sessile serrated adenomas (SSAs).

METHODS

We conducted a retrospective study to identify patients with SSAs using a university-based hospital pathology database query from January 2007 to April 2011. Data collected included: age, gender, ethnicity, body mass index, diabetes, smoking, family history of colorectal cancer, aspirin, and statin use. We collected data on morphology of SSAs including site (proximal or distal), size, and endoscopic appearance (flat or protuberant). We also compared proximal SSAs to proximal tubular adenomas detected during same time period.

RESULTS

One hundred and twenty patients with SSAs were identified: 61% were distal and 39% were proximal SSAs. Proximal SSAs were more likely to be flat than distal (100% vs 78% respectively; P = 0.0001). Proximal SSAs were more likely to occur in smokers (OR = 2.63; 95%CI: 1.17-5.90; P = 0.02) and in patients with family history of colorectal cancer (OR = 4.72; 95%CI: 1.43-15.55; P = 0.01) compared to distal. Proximal SSAs were statistically more likely to be ≥ 6 mm in size (OR = 2.94; P = 0.008), and also more likely to be large (≥ 1 cm) (OR = 4.55; P = 0.0005) compared to the distal lesions. Smokers were more likely to have proximal (P = 0.02), flat (P = 0.01) and large (P = 0.007) SSAs compared to non-smokers. Compared to proximal tubular adenomas, proximal SSAs were more likely to be large and occur in smokers.

CONCLUSION

Proximal SSAs which accounted for two-fifths of all SSAs were more likely to present as flat lesions, larger SSAs, and were more likely to occur in smokers and in patients with family history of colorectal cancer. Our data has implications for colorectal cancer screening.

Missed lesions at CT colonography: lessons learned

Misinterpretation at CT colonography (CTC) can result in either a colorectal lesion being missed (false-negative) or a false-positive diagnosis. This review will largely focus on potential missed lesions-and ways to avoid such misses. The general causes of false-negative interpretation at CTC can be broadly characterized and grouped into discrete categories related to suboptimal study technique, specific lesion characteristics, anatomic location, and imaging artifacts. Overlapping causes further increase the likelihood of missing a clinically relevant lesion. In the end, if the technical factors of bowel preparation, colonic distention, and robust CTC software are adequately addressed on a consistent basis, and the reader is aware of all the potential pitfalls at CTC, important lesions will seldom be missed.

Evaluation of colonic lesions and pitfalls in CT colonography: a systematic approach based on morphology, attenuation and mobility

Computed tomographic colonography is a reliable technique for the detection and classification of neoplastic and non-neoplastic lesions of the colon. It is based on a thin-section CT dataset of the cleansed and air-distended colon, acquired in prone and supine position. Two-dimensional and 3D projections are used in combination for image interpretation. The evaluation of CT colonography datasets is based on two steps, lesion perception to detect a polyp candidate and image interpretation to correctly characterize colonic filling defects. A thorough knowledge of the morphologic and attenuation characteristics of common colonic lesions and artifacts facilitates characterization of the findings. The purpose of this review article is to give an overview of the key CT colonographic imaging criteria to correctly characterize common colorectal lesions and to identify typical pitfalls and pseudolesions.

Current status on performance of CT colonography and clinical indications

CT colonography (CTC) is a robust and reliable imaging test of the colon. Accuracy for the detection of colorectal cancer (CRC) is as high as conventional colonoscopy (CC). Identification of polyp is size dependent, with large lesions (≥10mm) accurately detected and small lesions (6-9mm) identified with moderate to good sensitivity. Recent studies show good sensitivity for the identification of nonpolypoid (flat) lesions as well. Current CTC indications include the evaluation of patients who had undergone a previous incomplete CC or those who are unfit for CC (elderly and frail individuals, patients with underlying severe clinical conditions, or with contraindication to sedation). CTC can also be efficiently used in the assessment of diverticular disease (excluding patients with acute diverticulitis, where the exam should be postponed), before laparoscopic surgery for CRC (to have an accurate localization of the lesion), in the evaluation of colonic involvement in the case of deep pelvic endometriosis (replacing barium enema). CTC is also a safe procedure in patients with colostomy. For CRC screening, CTC should be considered an opportunistic screening test (not available for population, or mass screening) to be offered to asymptomatic average-risk individuals, of both genders, starting at age 50. The use in individuals with positive family history should be discussed with the patient first. Absolute contraindication is to propose CTC for surveillance of genetic syndromes and chronic inflammatory bowel diseases (in particular, ulcerative colitis). The use of CTC in the follow-up after surgery for CRC is achieving interesting evidences despite the fact that literature data are still relatively weak in terms of numerosity of the studied populations. In patients who underwent previous polypectomy CTC cannot be recommended as first test because debate is still open. It is desirable that in the future CTC would be the first-line and only diagnostic test for colonic diseases, leaving to CC only a therapeutic role.

Computer-aided detection of colorectal polyps in CT colonography with and without fecal tagging: a stand-alone evaluation

PURPOSE

To evaluate the stand-alone performance of a computer-aided detection (CAD) algorithm for colorectal polyps in a large heterogeneous CT colonography (CTC) database that included both tagged and untagged datasets.

METHODS

Written, informed consent was waived for this institutional review board-approved, HIPAA-compliant retrospective study. CTC datasets from 2063 patients were assigned to training (n = 374) and testing (n = 1689). The test set consisted of 836 untagged and 853 tagged examinations not used for CAD training. Examinations were performed at 15 sites in the United States, Asia, and Europe, using 4- to 64-multidetector-row computed tomography and various acquisition parameters. CAD sensitivities were calculated on a per-patient and per-polyp basis for polyps measuring ≥6 mm. The reference standard was colonoscopy in 1588 (94%) and consensus interpretation by expert radiologists in 101 (6%) patients. Statistical testing employed χ, logistic regression, and Mann-Whitney U tests.

RESULTS

In 383 of 1689 individuals, 564 polyps measuring ≥6 mm were identified by the reference standard (347 polyps: 6-9 mm and 217 polyps: ≥10 mm). Overall, CAD per-patient sensitivity was 89.6% (343/383), with 89.0% (187/210) for untagged and 90.2% (156/173) for tagged datasets (P = 0.72). Overall, per-polyp sensitivity was 86.9% (490/564), with 84.4% (270/320) for untagged and 90.2% (220/244) for tagged examinations (P = 068). The mean false-positive rate per patient was 5.14 (median, 4) in untagged and 4.67 (median, 4) in tagged patient datasets (P = 0.353).

CONCLUSION

Stand-alone CAD can be applied to both tagged and untagged CTC studies without significant performance differences. Detection rates are comparable to human readers at a relatively low false-positive rate, making CAD a useful tool in clinical practice.

Initial experience with computed tomographic colonography applied for noncolorectal cancerous conditions

PURPOSE

The aim of this study was to asses retrospectively the performance of computed tomography colonography (CTC) for noncolorectal cancerous conditions.

MATERIAL AND METHODS

A total of 44 patients with non-colorectal cancerous conditions underwent CTC. We researched the indications for CTC or present illness and evaluated the CTC imaging findings. We assessed whether diagnosis by CTC reduced conventional colonoscopic examinations.

RESULTS

A total of 47 examinations were performed in 44 patients. The indications for CTC or a present illness were as follows: 15 patients with impossible or incomplete colonoscopy, 7 with diverticular disease, 6 with malignancy (noncolorectal cancer), 6 with Crohn's disease, 4 suspected to have a submucosal tumor on colonoscopy, 2 with ischemic colitis, and 4 with various other diseases. Colonic findings were diagnosed on CTC in 36 examinations, and extracolonic findings were identified in 35 of 44 patients. In all, 17 patients had undergone colonoscopy previously, 9 (52.9%) of whom did not require further colonoscopy by CTC. Five patients underwent colonoscopy after CTC.

CONCLUSION

The indications for CTC were varied for patients with noncolorectal cancerous conditions. CTC examinations could be performed safely. Unlike colonoscopy or CT without preparation, CTC revealed colonic and extracolonic findings and may reduce the indication of colonoscopy in patients with noncolorectal cancerous conditions.

Fecal-tagging CT colonography with structure-analysis electronic cleansing for detection of colorectal flat lesions

PURPOSE

To evaluate the feasibility and sensitivity of the 3D-reading of fecal-tagging CT colonography (CTC) with a novel structure-analysis electronic cleansing (SAEC) in detecting colorectal flat lesions in comparison with a cleansed 3D reading with Viatronix V3D Colon system (V3D) and primary uncleansed 2D reading (2D).

MATERIALS AND METHODS

Forty CTC cases with flat lesions were retrospectively observed. The Subjects from a multicenter clinical trial underwent cathartic bowel preparation with orally administrated barium-based fecal-tagging. Sixty-nine flat lesions were confirmed using colonoscopy and histopathology as a reference standard. The results from SAEC reading were compared with those of prospective V3D and 2D readings.

RESULTS

Overall detection sensitivity with SAEC was 52% (36/69), which was statistically higher than that of 32% (22/69) and 29% (20/69) with V3D and 2D readings, respectively (p<0.05). The sensitivities in detecting not-on-fold flat lesions were 63% (24/38), 45% (17/38), and 42% (16/38) with SAEC, V3D, and 2D readings, respectively; whereas those of on-fold flat lesions were 39% (12/31), 16% (5/31), and 13% (4/31), respectively. None of the eight flat lesions (2-9mm) at cecum was detected by any of the three reading methods. Excluding the flat lesions at cecum, the sensitivity with SAEC for detecting flat lesion ≥4mm increased to 84% (31/37).

CONCLUSIONS

The fecal-tagging CTC with structure-analysis electronic cleansing could yield a high sensitivity for detecting flat lesions ≥4mm. The not-on-fold flat lesions were detected with higher sensitivity than on-fold flat lesions.

Colon segmentation for prepless virtual colonoscopy

A novel segmentation framework for a prepless virtual colonoscopy (VC) is presented, which reduces the necessity for colon cleansing before the CT scan. The patient is injected rectally with a water-soluble iodinated contrast medium using manual insufflators and a small rectal catheter. Compared to the air-based contrast medium, this technique can better preserve the color lumen and reduce the partial volume effect. However, the contrast medium, together with the fecal materials and air, makes colon wall segmentation challenging. Our solution makes no assumptions about the shape, size, and location of the fecal material in the colon. This generality allows us to label the fecal material accurately and extract the colon wall reliably. The accuracy of our technique has been verified on 60 human subjects. Compared with current VC technologies, our method is shown to be better in terms of both sensitivity and specificity. Further, in our experiments, the accuracy of the technique was comparable to that of optical colonoscopy results.

Risk factors and diagnosis of flat adenomas of the colon

In addition to histology, size and location, a morphologic description can be ascribed to polyps and adenomas. Traditionally, adenomas have been described as sessile and pedunculated, but it is now accepted that they can also present as flat or even depressed. Although first recognized in 1985, flat adenomas have become more common in Western published literature and in endoscopic reports. The Japanese Research Society Classification describes flat adenomas as lesions with a height that is less than one half of the diameter, while the Paris classification divides polyps into protruding and nonprotruding. The clinical significance of flat adenomas includes their potential malignancy, difficulty in detection and possible role in interval cancers. Serrated polyps represent a subset of polyps that have all the features that make flat lesions clinically important. Due to the relatively recent recognition of these lesions, as well as the technology required to detect them, the prevalence and malignant potential of these lesions in Western patients are still unknown. Finally, the best techniques and equipment for detecting flat polyps are also not established. In this article, we examine the issue of flat polyps and their significance in colorectal cancer screening with regard to prevalence, risk factors and methods for detecting flat polyps.

Comparison of accuracy and time-efficiency of CT colonography between conventional and panoramic 3D interpretation methods: an anthropomorphic phantom study

PURPOSE

To retrospectively compare the conventional three-dimensional (3D) interpretation method with the panoramic 3D method with regard to accuracy and time-efficiency in the detection of colonic polyps, using pig colonic phantoms as the standard of reference.

MATERIALS AND METHODS

One-hundred and sixty-two polyps were created in 18 pig colonic phantoms. CT colonography was performed with a 64-row detector CT scanner. Two-week interval reviews for the CTC image dataset with both the conventional and the panoramic 3D interpretation method were independently performed by three radiologists. The sensitivities of both methods were compared with the McNemar test. The mean interpretation time for each interpretation method was also assessed and compared with the Wilcoxon signed-rank test.

RESULTS

Compared with the conventional 3D method (0.96 for reader 1, 0.89 for reader 2, and 0.97 for reader 3), the panoramic method revealed comparable sensitivities (0.91 for reader 1, 0.86 for reader 2, and 0.93 for reader 3) (p>0.05). Interpretation time was significantly shorter with the panoramic method (115.1±32.7 s for reader 1, 229.7±72.2 s for reader 2, and 282.6±113.7 s for reader 3) than with the conventional method (218.9±59.9 s for reader 1, 379.4±117.0 s for reader 2, and 458.7±149.4 s for reader 3) for all readers (p<0.05).

CONCLUSION

Compared with the conventional 3D interpretation method, the panoramic 3D interpretation method shows improved time-efficiency and comparable sensitivity in the detection of colonic polyps.

Flat colon polyps: what should radiologists know?

With the recent publication of international computed tomography (CT) colonography standards, which aim to improve quality of examinations, this review informs radiologists about the significance of flat polyps (adenomas and hyperplastic polyps) in colorectal cancer pathways. We describe flat polyp classification systems and propose how flat polyps should be reported to ensure patient management strategies are based on polyp morphology as well as size. Indeed, consistency when describing flat polyps is of increasing importance given the strengthening links between CT colonography and endoscopy.

Colorectal cancer screening: The role of CT colonography

Computed tomography colonography (CTC) in colorectal cancer (CRC) screening has two roles: one present and the other potential. The present role is, without any further discussion, the integration into established screening programs as a replacement for barium enema in the case of incomplete colonoscopy. The potential role is the use of CTC as a first-line screening method together with Fecal Occult Blood Test, sigmoidoscopy and colonoscopy. However, despite the fact that CTC has been officially endorsed for CRC screening of average-risk individuals by different scientific societies including the American Cancer Society, the American College of Radiology, and the US Multisociety Task Force on Colorectal Cancer, other entities, such as the US Preventive Services Task Force, have considered the evidence insufficient to justify its use as a mass screening method. Medicare has also recently denied reimbursement for CTC as a screening test. Nevertheless, multiple advantages exist for using CTC as a CRC screening test: high accuracy, full evaluation of the colon in virtually all patients, non-invasiveness, safety, patient comfort, detection of extracolonic findings and cost-effectiveness. The main potential drawback of a CTC screening is the exposure to ionizing radiation. However, this is not a major issue, since low-dose protocols are now routinely implemented, delivering a dose comparable or slightly superior to the annual radiation exposure of any individual. Indirect evidence exists that such a radiation exposure does not induce additional cancers.

CT colonography and non-polypoid colorectal neoplasms

Computed tomographic colonography (CTC) has been reported to be as effective as optical colonoscopy in the detection of significant adenomas. However, there are widely conflicting performance data in relation to detection of flat neoplasia. This article describes the potential and limitations of CTC and computer-aided diagnosis in the detection of flat neoplasms.

Increasing computer-aided detection specificity by projection features for CT colonography

PURPOSE

A large number of false positives (FPs) generated by computer-aided detection (CAD) schemes is likely to distract radiologists' attention and decrease their interpretation efficiency. This study aims to develop projection-based features which characterize true and false positives to increase the specificity while maintaining high sensitivity in detecting colonic polyps.

METHODS

In this study, two-dimensional projection images are obtained from each initial polyp candidate or volume of interest, and features are extracted from both the gray and color projection images to differentiate FPs from true positives. These projection features were tested to exclude different types of FPs, such as haustral folds, rectal tubes, and residue stool using a database of 325 patient studies (from two different institutions), which includes 556 scans at supine and/or prone positions with 347 polyps and masses sized from 5 to 60 mm. For comparison, several well-established features were used to generate a baseline reference. The experimental evaluation was conducted for large polyps (> or = 10 mm) and medium-sized polyps (5-9 mm) separately.

RESULTS

For large polyps, the additional usage of the projection features reduces the FP rate from 5.31 to 1.92 per scan at the comparable by-polyp sensitivity level of 93.1%. For medium-sized polyps, the FP rate is reduced from 8.89 to 5.23 at the sensitivity level of 80.6%. The percentages of FP reduction are 63.9% and 41.2% for the large and medium-sized polyps, respectively, without sacrificing detection sensitivity.

CONCLUSIONS

The results have demonstrated that the new projection features can effectively reduce the FPs and increase the detection specificity without sacrificing the sensitivity. CAD of colonic polyps is supposed to help radiologists to improve their performance in interpreting computed tomographic colonography images.

Flat (nonpolypoid) colorectal lesions identified at CT colonography in a U.S. screening population

RATIONALE AND OBJECTIVES

The aim of this study was to investigate the clinical importance and height definition of flat (nonpolypoid) colorectal lesions detected on screening computed tomographic colonography (CTC).

MATERIALS AND METHODS

Results from prospective screening CTC in 5107 consecutive asymptomatic adults (mean age, 56.9 years) at a single center were analyzed. All detected colorectal lesions > or = 6 mm were prospectively categorized as polypoid or flat (nonpolypoid). The maximal height of all flat lesions was measured to assess the suggested 3-mm threshold definition.

RESULTS

Of 954 polyps measuring > or = 6 mm identified on screening CTC, 125 lesions (13.1%) in 106 adults were prospectively categorized as flat, with a mean size of 12.7 mm (range, 6-80 mm), including 73 lesions 6 to 9 mm, 42 lesions 10 to 29 mm, and 10 lesions > or = 3 cm (carpet lesions). For polyps between 6 and 30 mm in size, flat lesions were less likely than polypoid lesions to be neoplastic (25.0% vs 60.3%, P < .001), histologically advanced (5.4% vs 12.1%, P = .07) or malignant (0% vs 0.5%, P = NS). Two of 10 carpet lesions (20%) were malignant, compared to 50% of polypoid masses > or = 3 cm. Of nine flat lesions seen only on colonoscopy (false-negatives on CTC), two were neoplastic (tubular adenomas), and none was histologically advanced. For all flat lesions between 6 and 30 mm, the maximal height averaged 2.2 mm and was < or =3 mm in 86.1%, including 93.2% of small 6-mm to 9-mm flat lesions.

CONCLUSION

In a US screening population, flat colorectal lesions detected on CTC demonstrated less aggressive histologic features compared to polypoid lesions. Excluding carpet lesions, a maximal height of 3 mm appears to be a reasonable definition.

Association of smoking and flat adenomas: results from an asymptomatic population screened with a high-definition colonoscope

BACKGROUND

Flat adenomas represent a morphologically distinct class of polyps that may be difficult to detect, and little is known regarding risk factors for these lesions. Identification of risk factors for these lesions may aid in colorectal cancer (CRC) screening, because patients at risk for these lesions may require special imaging techniques. Smoking, an important risk factor for CRC, may be associated with molecular changes that increase the risk for flat adenomas.

OBJECTIVE

The aim of this study was to examine the association between smoking and flat adenomas.

DESIGN

Prospective cross-sectional study.

SETTING

University hospital endoscopy center.

PATIENTS

We enrolled asymptomatic patients presenting for CRC screening.

INTERVENTIONS

We screened patients with a high-definition (1080i signal) wide-angle (170 degrees field of view) Olympus 180-series colonoscope. We collected demographics, medication use, family history of CRC, diet history, and smoking history.

MAIN OUTCOME MEASUREMENTS

Polyp morphology, assessed by using the Japanese Research Society Classification (JRSC).

RESULTS

A total of 600 patients were enrolled. We observed that smoking was associated with having a flat adenoma of any size (adjusted odds ratio [OR], 2.53; 95% CI, 1.60-4.00), having only flat adenomas that were > or = 6 mm in diameter (adjusted OR, 3.84; 95% CI, 2.02-7.32), as well as flat advanced adenomas (adjusted OR, 2.81; 95% CI, 1.08-7.30).

LIMITATIONS

The study design may not account for some confounding variables and provides no information regarding smoking status at the time of initiation of flat adenomas.

CONCLUSION

Smoking was associated with flat adenomas in our population. Our findings may explain the earlier onset of CRC in smokers as well as the advanced stage with which they present, with compared with nonsmokers. Smokers may require screening with high-definition colonoscopes to detect flat adenomas.

Performance of CT colonography for detecting small, diminutive, and flat polyps

The primary goal of colorectal cancer screening and prevention is the detection and removal of advanced neoplasia. Computerized tomography (CT) colonography is now well established as an effective screening test. Areas of greater uncertainty include the performance characteristics of CT colonography for detecting small (6-9 mm), diminutive (< or =5 mm), and flat (nonpolypoid) lesions. However, the actual clinical relevance of small, diminutive, and flat polyps has also been the source of debate. This article addresses these controversial and often misunderstood issues.

ACR Colon Cancer Committee white paper: status of CT colonography 2009

PURPOSE

To review the current status and rationale of the updated ACR practice guidelines for CT colonography (CTC).

METHODS

Clinical validation trials in both the United States and Europe are reviewed. Key technical aspects of the CTC examination are emphasized, including low-dose protocols, proper insufflation, and bowel preparation. Important issues of implementation are discussed, including training and certification, definition of the target lesion, reporting of colonic and extracolonic findings, quality metrics, reimbursement, and cost-effectiveness.

RESULTS

Successful validation trials in screening cohorts both in the United States with ACRIN and in Germany demonstrated sensitivity > or = 90% for patients with polyps >10 mm. Proper technique is critical, including low-dose techniques in screening cohorts, with an upper limit of the CT dose index by volume of 12.5 mGy per examination. Training new readers includes the requirement of interactive workstation training with 2-D and 3-D image display techniques. The target lesion is defined as a polyp > or = 6 mm, consistent with the American Cancer Society joint guidelines. Five quality metrics have been defined for CTC, with pilot data entered. Although the CMS national noncoverage decision in May 2009 was a disappointment, multiple third-party payers are reimbursing for screening CTC. Cost-effective modeling has shown CTC to be a dominant strategy, including in a Medicare cohort.

CONCLUSION

Supported by third-party payer reimbursement for screening, CTC will continue to further transition into community practice and can provide an important adjunctive examination for colorectal screening.

Comparison of 2D and 3D views for evaluation of flat lesions in CT colonography

RATIONALE AND OBJECTIVES

Flat lesions in the colon may result in false-negative computed tomography colonography interpretations. It is unknown whether flat lesions are better measured on two-dimensional (2D) or three-dimensional (3D) images and which settings are optimal for enhanced reproducibility and decreased variability. We evaluated these factors to determine whether 2D or 3D is best for flat lesion measurements.

METHODS AND MATERIALS

Eighty-eight lesions in 66 patients from a previously published clinical trial were analyzed. Lesions were viewed with four methods including 2D at three window/level settings and 3D endoluminal view. Lesions in either supine or prone were counted as one dataset. Long axis and height were measured. Criteria of "height" (<or=3 mm high) or "ratio" (height <or=half the long axis) were applied. A subset of lesions was subject to inter- and intra-observer variability analysis.

RESULTS

With the "height" criterion, more datasets were classified as flat in 2D flat (n = 76), 2D soft tissue (n = 82), and 3D (n = 73) views than in the 2D lung (n = 49) view. If long axis is used as the key metric, endoluminal 3D (12.1%) views significantly showed the least inter-observer variability compared to lung (18.9%) or soft tissue (20.2%) views. Intra-observer variability was low overall for all methods.

CONCLUSION

When characterizing lesions as flat, a consistent viewing method should be used. To minimize inter-observer variability (such as when following a patient over time), it is best to use the ratio criterion for flat lesion definition incorporating the single longest dimension on 3D views as the key metric.

Automated measurement of colorectal polyp height at CT colonography: hyperplastic polyps are flatter than adenomatous polyps

OBJECTIVE

Hyperplastic polyps are more difficult to detect than adenomatous polyps at CT colonography (CTC), and it has been theorized that this difference in detectability is because hyperplastic polyps are flatter. Using automated software that computes polyp height, we determined whether hyperplastic colonic polyps on CTC are indeed flatter than adenomatous polyps of comparable width.

MATERIALS AND METHODS

At three medical centers, 1,186 patients underwent oral contrast-enhanced CTC and same-day optical colonoscopy (OC) with segment unblinding for colorectal cancer screening. One hundred eighty-five of the patients had at least one hyperplastic or adenomatous polyp 6-10 mm visible at both OC and CTC, where size was determined by a calibrated guidewire at OC. To assess flatness, the heights of the polyps at CTC were measured using a validated automated software program. The heights and height-to-width ratios of the hyperplastic polyps were compared with those of the adenomatous polyps using a Student's t test (two-tailed, unpaired, unequal variance).

RESULTS

There were 176 adenomatous and 83 hyperplastic polyps visible at segment-unblinded OC. The fraction of these polyps that were measurable at CTC using the automated software was not significantly different for adenomatous versus hyperplastic polyps (158/176 [89.8%] vs 73/87 [83.9%], respectively; p = 0.2). The average height-to-width ratios using automated width measurements were 15% less for hyperplastic polyps: 0.39 +/- 0.20 (n = 158) and 0.33 +/- 0.19 (n = 73) for adenomatous and hyperplastic polyps, respectively (p = 0.03). When polyps of comparable OC size or CTC width were considered, the heights of hyperplastic polyps were up to 27% less than those of adenomatous polyps.

CONCLUSION

For 6-10 mm polyps of a given size as determined by OC or a given width at CTC, hyperplastic polyps tend to be flatter (i.e., have lower height) compared with adenomatous polyps.

Flat lesions in CT colonography

Flat lesions have been a source of controversy because of concerns that CT colonography (CTC) is insensitive in detecting these lesions, yet they may harbor a high incidence of advanced neoplasia. The wide variation in the reported incidence of flat lesions may in part be due to the lack of a uniform definition of "flat", and in fact in many prior reports the inclusion criteria for flat are not even clearly specified. Emphasis on the more recent CTC literature suggests that when limited the target lesion to neoplasia (adenomas or adenocarcinoma), the incidence of flat lesions is low and most can be detected by CTC. Using fecal tagging and careful attention to the proper methods of searching for flat lesions with both 3D and 2D techniques can maximize the detection of flat lesions at CTC. Computer-aided detection may be helpful.

Sensitivity of CT colonography for nonpolypoid colorectal lesions interpreted by human readers and with computer-aided detection

OBJECTIVE

The purpose of our study was to determine the sensitivity of CT colonography (CTC) interpreted by human readers and with computer-aided detection (CAD) for genuinely nonpolypoid colorectal lesions, defined as 2 mm or less in lesion height at colonoscopy.

MATERIALS AND METHODS

A computerized database search for a 33-month period found 21 patients who had undergone both colonoscopy and CTC and who had a total of 23 genuinely nonpolypoid colorectal lesions: eight adenomas (9-30 mm in width), 10 stage Tis or T1 adenocarcinomas (10-25 mm), and five nonadenomatous lesions (8-20 mm). CTC was performed using a cathartic preparation and fecal tagging and was interpreted by experienced readers in a blinded manner using a primary 3D method and with CAD.

RESULTS

The sensitivities of human readers for nonpolypoid adenomatous lesions (i.e., both adenomas and adenocarcinomas), adenocarcinomas, and nonadenomatous lesions were 66.7% (12/18), 90% (9/10), and 0% (0/5), respectively. Sensitivities were 55.6% (10/18), 90% (9/10), and 0% (0/5) for CAD. A 10-mm stage T1 adenocarcinoma was missed by a human reader on blinded review but was detected with CAD. Both human readers and CAD yielded significantly higher sensitivity for adenomatous lesions than for nonadenomatous lesions (p = 0.014 and 0.046, respectively) and for adenocarcinomas than for noncancerous lesions (p = 0.003 and 0.0001, respectively).

CONCLUSION

CTC showed a high sensitivity for nonpolypoid stage Tis and T1 adenocarcinomas 10 mm or greater in width despite the limited overall sensitivity for nonpolypoid adenomatous lesions, when performed using cathartic preparation and fecal tagging.

Colorectal cancer screening with CT colonography: key concepts regarding polyp prevalence, size, histology, morphology, and natural history

OBJECTIVE

The purpose of this article is to provide a timely update on a variety of key polyp topics to construct a proper framework for physicians who are interested in providing CT colonography screening as a clinical service.

CONCLUSION

As the medical community considers the expansion of CT colonography for screening, we believe it is prudent to update and review several key concepts regarding colorectal polyps. In particular, it is important to replace the older literature derived from high-risk and symptomatic cohorts with the wealth of newer and more applicable data from average-risk and asymptomatic screening cohorts. Familiarity with current concepts regarding flat (nonpolypoid) lesions and the natural history of small colorectal polyps is also vital to the effective application of this technique.

Conspicuity of colorectal polyps at CT colonography: visual assessment, CAD performance, and the important role of polyp height

RATIONALE AND OBJECTIVES

The factors that influence the conspicuity of polyps on computed tomographic (CT) colonography (CTC) are poorly understood. The aim of this study is to compare radiologists' visual assessment of polyp conspicuity to quantitative image features and show the relationship between visual conspicuity and the detection of colonic polyps by computer-aided detection (CAD) on CTC.

METHODS

One polyp (size range 6-10 mm) was selected from the CTC examination of each of 29 patients from a larger cohort. All patients underwent oral contrast-enhanced CTC with same-day optical colonoscopy with segmental unblinding. The polyps were analyzed by a previously validated CAD system and placed into one of two groups (detected [n = 12] or not detected [n = 17] by CAD). The study population was intentionally enriched with polyps that were not detected by the CAD system. Four board-certified radiologists, blinded to the CAD results, reviewed two- and three-dimensional CTC images of the polyps and scored the conspicuity of the polyps using a 4-point scale (0 = least conspicuous, 3 = most conspicuous). Polyp height and width were measured by a trained observer. A t-test (two-tailed, unpaired equal variance) was done to determine statistical significance. Intra- and interobserver variabilities of the conspicuity scores were assessed using the weighted kappa test. Regression analysis was used to investigate the relationship of conspicuity to polyp height and width.

RESULTS

A statistically significant difference was found between the average conspicuity scores for polyps that were detected by CAD compared to those that were not (2.3 +/- 0.6 vs. 1.4 +/- 0.8) (P = .004). There was moderate intraobserver agreement of the conspicuity scores (weighted kappa 0.57 +/- 0.09). Interobserver agreement was fair (average weighted kappa for six pair-wise comparisons, 0.38 +/- 0.15). Conspicuity was correlated with manual measurement of polyp height (r(2) = 0.38-0.56, P < .001).

CONCLUSIONS

This CAD system tends to detect 6-10 mm polyps that are more visually conspicuous. Polyp height is a major determinant of visual conspicuity. The generalizability of these findings to other CAD systems is currently unknown. Nevertheless, CAD developers may need to specifically target flatter and less conspicuous polyps for CAD to better assist the radiologist to find polyps in this clinically important size category.