Diagnostic accuracy and interobserver agreement of CT colonography (virtual colonoscopy)

BACKGROUND AND AIMS: Computed tomographic (CT) colonography or virtual colonoscopy (VC) is a non-invasive imaging method proposed for screening patients with colorectal neoplasias. Our aims were to study the diagnostic accuracy and interobserver agreement of VC for correct patient identification compared with conventional colonoscopy (CC). METHODS: This was a prospective study of 50 patients successively undergoing VC and CC. Multiplanar two dimensional CT images and three dimensional VC were constructed using surface rendering software and interpreted by two independent investigator teams. VC findings were compared with those of CC. Interobserver agreement was determined using kappa statistics. RESULTS: CC found 65 polyps in 24 patients. For identification of patients with polyps > or =10 mm, the sensitivity of VC was 38% and 63%, and specificity was 74% and 74% for teams 1 and team 2. Interobserver agreement was good (kappa 0.72). For patients with polyps of any size, the sensitivity of VC was 75% and 71%, and specificity was 62% and 69% for teams 1 and 2. Interobserver agreement was fair (kappa 0.56). Accuracy improved when comparing the results of the first 24 with the last 26 patients. CONCLUSIONS: In our experience, VC had a low diagnostic value for identification of patients with colorectal neoplasias. Interobserver agreement for VC interpretation was fair. These results may be explained by software imperfections and a learning curve effect.     

CT colonography (virtual colonoscopy): technique, indications and performance

Worldwide, colorectal cancer is the third most frequent cancer occurring in both sexes. Screening programs for early detection enable detection of tumors at an earlier stage and have been shown to reduce death rate. Currently, colonoscopy is the investigation of choice for colorectal cancer screening and for investigation of patients with suspected colorectal cancer. However, colonoscopy remains an invasive technique requiring anesthesia, with a risk of perforation and bleeding. In addition, even experienced colonoscopists may be unable to complete the colonoscopy due to multiple reasons such as severe diverticulosis, stricture, obstructing mass, or fixation of colonic loops. CT colonography, also known as virtual colonoscopy, is a relatively new technique that is becoming increasingly popular. The technical aspects, indications, advantages and diagnostic performance of this technique are briefly reviewed.     

Clinical significance of virtual colonoscopy (CT colonography) with special reference to polyp morphology

BACKGROUND/AIMS: Computed tomographic colonography [virtual colonoscopy (VC)] is a new imaging method that may contribute to the detection of colorectal neoplasms. The aim of this study was to investigate the clinical significance of VC for the diagnosis of colorectal tumors with special reference to their morphology. METHODOLOGY: Sixteen patients with colorectal tumors were enrolled in this study. Colonic preparation was performed using magnesium sulfate, and scopolamine butylbromide was injected before air insufflation from the anus. VC was performed with an Aquilion multislice CT system (Toshiba) and Workstation M900 maximum (ZIO). The results were compared with those of conventional colonoscopy (CC). In six cases, total colonoscopy was not possible due to tumor stricture. RESULTS: The number of lesions detected by CC was 58; 48 early carcinomas/adenomas (group A) and 10 advanced carcinomas (group B). All group B lesions and 43.8% (21 lesions) of group A lesions were identified by VC. The specificity of VC for group A and B lesions was 45.8% and 100%, respectively. There was no significant difference in detection rate for group A lesions by subclassification according to their morphology: pedunculated; 22% (2/9), semipedunculated; 50% (6/12), sessile; 29% (4/14), superficially elevated; 56% (5/9), and superficially elevated morphology with central depression; 100% (4/4). The mean diameter of the lesions that were detected and not detected by VC was 7+/-8.0 mm (range: 3-30 mm) and 8+/-5.8 mm (range: 2-20 mm), respectively (P=0.90). CONCLUSIONS: Polyps with superficial morphology could be detected by VC as well as those with protuberant morphology. According to evidence that neither the morphology nor the size of a lesion was a significant factor for detection by VC, the authors consider that the diagnostic ability of VC may be improved by better preparation.     

Findings on optical colonoscopy after positive CT colonography exam

BACKGROUND & AIMS:  The aim of this study is to evaluate the findings on optical colonoscopy (OC) after a positive CT colonography (CTC) exam and characterize the type of polyps seen on OC but not reported by CTC.
METHODS:  Over an 18-month period a total of 159 asymptomatic adults had polyps seen on computed tomography colonography examination and subsequently underwent planned therapeutic optical colonoscopy. The colonoscopists were aware of the findings on CT colonography prior to further evaluation of the colon. Characteristics of polyps and adenomas seen on subsequent optical colonoscopy but not seen or reported on CT colonography were examined.
RESULTS:  The adenoma miss rate for CT colonography overall was 18.9% (25/132) including 6.2% (4/65) for polyps >9 mm and 18.2% (8/44) for polyps 6–9 mm. Three of the adenomas >9 mm not seen on CTC were sessile, and two were found in patients with technically difficult CT colonography studies due to poor colonic distention. No adenomas with advanced pathology <6 mm were found on optical colonoscopy but not reported on CT colonography. False-positive CTC referral where no polyp was seen on colonoscopy was 5.0%.
CONCLUSIONS:  CT colonography has adenoma miss rates similar to miss rates historically found with optical colonoscopy, with most missed adenomas being <10 mm and sessile in shape.     

An analysis of the potential impact of computed tomographic colonography (virtual colonoscopy) on colonoscopy demand

BACKGROUND AND AIMS: There has been much speculation about the potential impact on the use of conventional colonoscopy if "virtual" computed tomographic colonography (CTC) became a widely accepted modality for colorectal cancer (CRC) screening. However, no formal analysis of the impact of CTC on colonoscopy demand has been reported. METHODS: A mathematical model to predict colonoscopy demand based on several relevant input parameters was constructed. Current national colonoscopy practice, estimated using various published reports, was used as the foundation to project colonoscopy demand if CTC were implemented as the primary CRC screening modality. RESULTS: In the base-case analysis, if CTC were used as the primary modality for CRC screening, 1.78 million colonoscopies could be eliminated from the total 6.47 million in 2003. Depending on the polyp size threshold used to define a CTC study as positive (6 or 10 mm), this loss would be partially offset by 1.21 million (6 mm) or .34 million (10 mm) follow-up colonoscopies for CTC examinations with positive findings, resulting in a net loss of .57 million (8.8% decrease) (6 mm) or 1.44 million (22.3% decrease) (10 mm). Extensive sensitivity analyses showed that the findings of this model were robust and insensitive to most parameters tested but were sensitive to a few parameters, including the percentage of CTC examinations with positive findings. CONCLUSIONS: Wide-scale implementation of CTC for CRC screening would likely lead to a decrease in use of conventional colonoscopy. The percentage of CTC studies with positive findings seemed to be a pivotal variable, which would be determined in large part by the polyp size ultimately established to define a positive finding.     

CT colonography: current status and future promise

CT colonography (CTC) is an innovative technology that entails CT examination of the entire colon and computerized processing of the raw data after colon cleansing and colonic distention. CTC could potentially increase the screening rate for colon cancer because of its relative safety, relatively low expense, and greater patient acceptance, but its role in mass colon cancer screening is controversial because of its highly variable sensitivity, the inability to sample polyps for histologic analysis, and lack of therapeutic capabilities. This article reviews the CTC literature, including imaging and adjunctive techniques, radiologic interpretation, procedure indications, contraindications, risks, sensitivity, interpretation pitfalls, and controversies.     

Virtual CT colonoscopy and virtual CT barium enema using multidetector-row CT]

CT colonography is a promising technique that provides both multiplanar and endoluminal perspective of the air-filled, distended, cleaned colon. "Virtual colonoscopy" refers to computer-simulated 3D endoscopic visualization of the colonic mucosal surface. Unlike barium enema and conventional colonoscopy, CT colonography can give cross- sectional and endoluminal images of the colon and enables to image extracolic abnormality. CT colonography offers potential advantages over colonoscopy in that it causes little discomfort to the patient, and does not need sedation. It is more accurate in spatial location of lesions and creates no complication. To date, most studies assessing CT colonography have focused in technical development, less aggressive bowel preparation, and computer-aided diagnosis of polyp detection. In the future, CT colonography would be a diagnostic and screening tool for the colorectal polyp and cancer.     

Patient preferences for CT colonography,conventional colonoscopy,and bowel preparation

OBJECTIVES: The aim of this study was to determine patient pre-examination expectations and postexamination appraisals for CT colonography, conventional colonoscopy and bowel preparation. METHODS: Prospective evaluation of 120 patients at defined risk for colorectal neoplasia was performed with CT colonography followed by colonoscopy on the same day. Subjects were stratified by age and sex (67 women and 53 men) and were randomized to receive either manual air (n = 61) or CO(2) (n = 59) insufflation during CT colonography. Patients' expectations were assessed just before the two examinations, and appraisals were assessed 2 to 3 days afterward regarding pain/discomfort, embarrassment, difficulty, overall assessment, preference for future testing, and bowel preparation. RESULTS: No significant differences were found in appraisals of manual air versus CO(2) insufflation techniques. For both CT colonography and colonoscopy, patients' appraisals after the procedure were significantly more positive than prior expectations. Patients expressed more favorable appraisals of colonoscopy for pain (p < 0.001) and embarrassment (p < 0.001), with most responses being "none" to "a little" for both examinations. Overall appraisals of the tests were favorable and similar between CT and colonoscopy: patients mainly expressed "not unpleasant" to "a little unpleasant" (95%, 114/120 for both examinations). Overall, appraisal of the bowel preparation was the most negative. Preferences for future testing were more favorable toward CT: of the patients, 58% (69/120) preferred CT, 14% (17/120) preferred colonoscopy, and 28% (34/120) had no preference. CONCLUSIONS: Overall appraisals were similar and positive for both CT colonography and colonoscopy, with less favorable appraisals of the bowel preparation. Most patients stated that they would prefer CT for future evaluation.     

Meta-analysis comparing CT colonography, air contrast barium enema, and colonoscopy

Introduction

Published studies have reported a wide range of sensitivities and specificities for computed tomographic (CT) colonography for polyp detection, generating controversy regarding its diagnostic accuracy.

Methods

A meta-analysis of published studies comparing the accuracies of CT colonography and colonoscopy for polyp detection was performed. The pooled per-patient sensitivities and specificities were calculated at various thresholds for polyp size. Summary receiver operating characteristic (sROC) curves were also constructed.

Results

Thirty studies were included in the meta-analysis of CT colonography. The pooled per-patient sensitivity of CT colonography was higher for polyps greater than 10 mm (0.82, 95% confidence interval [CI], 0.76-0.88) compared with polyps 6 to 10 mm (0.63, 95% CI, 0.52-0.75) and polyps 0 to 5 mm (0.56, 95% CI, 0.42-0.70). Similarly, the exact area under the sROC curve (area ± standard error) was higher using a threshold greater than 10 mm (0.898 ± 0.063) compared with thresholds of greater than 5 mm and any size (0.884 ± 0.033 and 0.822 ± 0.059, respectively). There were no significant differences in the diagnostic characteristics of 2-dimensional versus 3-dimensional CT colonography. At a threshold greater than 5 mm, the exact area under the sROC curve was significantly higher for endoscopic colonoscopy compared with CT colonography (0.998 ± 0.006 vs 0.884 ± 0.033, P < .005).

Conclusions

CT colonography has a reasonable sensitivity and specificity for detecting large polyps but was less accurate than endoscopic colonoscopy for smaller polyps. Thus, CT colonography may not be a reasonable alternative in situations in which a small polyp may be clinically relevant.     

CT colonography after incomplete colonoscopy in subjects with positive faecal occult blood test

AIM： To report our experience with computed tomography colonography （CTC） systematically performed in subjects with positive faecal occult blood test （FOBT） and an incomplete colonoscopy in the setting of a population-based screening for colorectal cancer （CRC）.
METHODS： From April 2006 to April 2007, 43 290 individuals （age range 50-70） who adhered to the regional screening program for the prevention of CRC underwent immunochemical FOBT. FOBT was positive in 1882 subjects （4.3%）. 1463 （77.7%） of these subjects underwent colonoscopy, 903 performed in a single center. Of 903 colonoscopies 65 （7.2%） were incomplete. Forty-two of these subjects underwent CTC. CTC was performed with a 16-MDCT scanner after standard bowel prep （polyethyleneglycole） in both supine and prone position. Subjects whose CTC showed polyps or masses were referred to the endoscopist for repeat colonoscopy under sedation or underwent surgery. Perlesion and per-segment positive predictive values （PPV） were calculated.
RESULTS： Twenty-one （50%） of 42 CTCs showed polyps or masses. Fifty-five of these subjects underwent a repeat colonoscopy, whereas 2 subjects underwent surgery for colonic masses of indeterminate nature. Four subjects refused further examinations. CTC correctly identified 2 colonic masses and 20 polyps. PPV for masses or polyps greater than 9 mm was of 87.5%. Per-lesion and per-segment PPV were, respectively, 83.3% and 83.3% for polyps greater or equal to 10 mm, and 77.8% and 85.7% for polyps of 6-9 mm.
CONCLUSION： In the context of a screening program for CRC based on FOBT, CTC shows high per-segment and per-lesion PPV for colonic masses and polyps greater than 9 mm. Therefore, CTC has the potential to become a useful technique for evaluation of the non visualized part of the colon after incomplete colonoscopy.     

Impact of a CT colonography screening program on endoscopic colonoscopy in clinical practice

OBJECTIVE: The potential effect of CT colonography (CTC) on endoscopic colonoscopy (EC) has been the topic of much speculation. The aim of this study was to evaluate the impact of a CTC screening program on colonoscopy in clinical practice. METHODS: At our institution a third-party reimbursed CTC colorectal cancer (CRC) screening program was established in 2004. The number of CTC monthly exams performed, monthly EC total and screening exams performed, EC with polypectomy performed, and the number of referrals for EC screening exams requested were prospectively examined in the first 33 months after introduction of a CTC CRC screening program. RESULTS: The mean number of overall (378.5 vs 413.1) and screening (150.7 vs 162.9) colonoscopy exams performed per month did not change significantly after screening CTC was introduced. The mean number of monthly CTC exams performed rose significantly throughout the first year of the study from 39 initially to a peak of 147.6 cases per month but decreased slightly to 114.3 monthly exams at the end of 2006. A mean 10.0 patients per month were sent for EC after a positive CTC exam. The mean number of monthly colonoscopies with polypectomy remained constant after the introduction of CTC (197.0 vs 180.2). Monthly referrals for screening EC exams initially decreased but were unchanged 3 yr after institution of a CTC screening program (255.0 vs 253.5). CONCLUSIONS: (a) In our tertiary care center the initiation of a screening CTC program did not result in a decrease in the number of total colonoscopy exams, screening colonoscopy exams performed, nor requests for screening colonoscopy. (b) Only a small number of CTC exams were referred for EC with polypectomy, therefore a CTC screening program may not increase the overall number of therapeutic colonoscopies performed.     

Three-dimensional MR and axial CT colonography versus conventional colonoscopy for detection of colon pathologies

AIM: To evaluate the sensitivity and specificity of MR colonography (MRC) and CT performance in detecting colon lesions, and to compare their sensitivity and specificity with that of conventional colonoscopy. METHODS: Forty-two patients suspected of having colonic lesions, because of rectal bleeding, positive fecal occult blood test results or altered bowel habits, underwent the examinations. After insertion of a rectal tube, the colon was filled with 1000-1500 mL of a mixture of 9 g/L NaCI solution, 15-20 mL of 0.5 mmol/L gadopentetate dimeglumine and 100 mL of iodinized contrast material. Once colonic distension was achieved, three-dimensional gradient-echo (3D-GRE) sequences for MR colonography and complementary MR images were taken in all cases. Immediately after MR colonography, abdominal CT images were taken by spiral CT in the axial and supine position. Then all patients were examined by conventional colonoscopy (CC). RESULTS: The sensitivity and specificity of MRC for colon pathologies were 96.4% and 100%, respectively. The percentage of correct diagnosis by MRC was 97.6%. The sensitivity and specificity of CT for colon pathologies were 92.8%, 100%, respectively. The percentage of correct diagnosis by CT was 95.2%. CONCLUSION: In detecting colon lesions, MRC achieved a diagnostic accuracy similar to CC. However, MRC is minimally invasive, with no need for sedation or analgesics during investigation. There is a lower percentage of perforation risk, and all colon segments can be evaluated due to multi-sectional imaging availability; intramural, extra-intestinal components of colonic lesions, metastasis and any additional lesions can be evaluated easily. MRC and CT colonography are new radiological techniques that promise to be highly sensitive in the detection of colorectal mass and inflammatory bowel lesions.     

CT仿真结肠镜在老年患者中的临床应用

目的探讨CT仿真结肠镜在老年患者中的临床价值。方法 75例高度怀疑存在结直肠病变却不能耐受或不愿接受结肠镜检查的老年患者,进行CT仿真结肠镜检查。结果 CT仿真结肠镜显示存在阳性病变61例,包括肿瘤53例,其中16例患者最后得到了手术治疗,经手术及术后病理得到进一步证实;另有良性狭窄病变8例。8例良性病变及14例阴性结果病例中有11例在6个月后得到复查,病情均无明显进展。结论 CT仿真结肠镜对老年患者的结直肠病变诊断具有较高的临床价值,是结肠镜检查的重要补充。     

CT仿真结肠镜与电子结肠镜对结直肠疾病诊断的对照研究

目的探讨CT仿真结肠镜(CTVC)在结直肠疾病,尤其是溃疡性结肠炎诊断中的价值。方法应用螺旋CT对2004年5月至2005年1月就诊于首都医科大学附属北京友谊医院的58例疑诊结直肠病变患者进行容积扫描,获取仿真结肠镜图像,将所得结果与结肠镜结果进行比较分析。结果CTVC检查均获得成功,共检出结直肠癌14例,结直肠息肉15例,溃疡性结肠炎14例,正常者6例。CTVC对结直肠疾病总的敏感性为82.7%(43/52),特异性为100%,准确性为84.5%(49/58),阳性预测值87.8%(43/49),阴性预测值40.0%(6/15),Kappa值为0.497;CTVC对溃疡性结肠炎诊断的敏感性为70.0%(14/20),特异性为100%,准确性为76.9%(20/26),阳性预测值70.0%(14/20),阴性预测值50.0%(6/12),Kappa值为0.519。结论CTVC是一种无创的检查方法,具有一定优势,但仍存在一些弊端,因此对于溃疡性结肠炎诊断仅是一种有效的补充,尚不能完全替代常规结肠镜检查。     

Colorectal polyp detection with virtual colonoscopy (computed tomographic colonography); the reliability of the method

BACKGROUND/AIMS: The aim of this study was to compare the reliability of virtual colonoscopy with conventional colonoscopy in detection of colorectal polyps. METHODOLOGY: Between November 1997 and February 2000, 23 patients (14 males, 9 females) aged 43-86 years (mean: 63) with colorectal polyps who underwent colonoscopy in our endoscopy unit, were referred for virtual colonoscopy. The colon was distended with an enema tube for rectal insufflation and subsequently was scanned by helical CT (Toshiba X-vision) using the following parameters: KV 120, mAs 200, table feed 5 mm/sec, slice thickness 5 mm and reconstruction intervals 2.5 mm. Using SPARC Station 20, virtual colonoscopy was generated. RESULTS: A total of 30 polyps (19 with diameter 8-15 mm and 11 larger than 15 mm) were detected with conventional colonoscopy. Virtual colonoscopy visualized 27 polyps (17 with diameter 8-15 mm and 10 with diameter > 15 mm). CONCLUSIONS: Virtual colonoscopy is a non-invasive, well-tolerated, safe technique and can be useful for detection of colorectal polyps. Weaknesses of the method are the inability to detect small lesions and to perform biopsies.