Usefulness of CT colonography in patients with incomplete colonoscopy

CT colonography: techniques, indications, findings

Computed tomographic colonography (CTC) is a minimally invasive technique for imaging the entire colon. Based on a helical thin-section CT of the cleansed and air-distended colon, two-dimensional and three-dimensional projections are used for image interpretation. Several clinical improvements in patient preparation, technical advances in CT, and new developments in evaluation software have allowed CTC to develop into a powerful diagnostic tool. It is already well established as a reliable diagnostic tool in symptomatic patients. Many experts currently consider CTC a comparable alternative to conventional colonoscopy, although there is still debate about its sensitivity for the detection of colonic polyps in a screening population. This article summarizes the main indications, the current techniques in patient preparation, data acquisition and data analysis as well as imaging features for common benign and malignant colorectal lesions.

Update on Colorectal Cancer Imaging

Colorectal cancer remains a leading cancer killer worldwide. The disease is both curable and preventable, and yet the importance of widespread screening is only now starting to be appreciated. This article reviews the variety of diagnostic tests, imaging procedures and endoscopic examinations available to detect colorectal cancer and polyps in their early stage and also presents details on various screening options. The critical role of the radiologist is elaborated on including accurate assessment of the tumor extent within the bowel wall and beyond and the detection of lymph node and distant metastases. Staging with CT, MR imaging, endorectal ultrasound, and positron emission tomography are of paramount importance in determining the most appropriate therapy and the risk of tumor recurrence and overall prognosis.

An update on imaging of colorectal cancer

Screening of asymptomatic average-risk patients for presence of colon cancer and early detection in precursor stages is of great interest to general population. Comprehensive evaluation of symptomatic or high-risk patients represents another important clinical focus. Available techniques for total colon imaging, rectal cancer staging and the role of positron emission tomography are discussed.

The diagnostic value of multiplanar reconstruction on MDCT colonography for the preoperative staging of colorectal cancer

The purpose of this study was to determine whether multiplanar reconstruction (MPR) images can improve the accuracy of MDCT-based colorectal cancer preoperative staging by receiver-operating characteristic (ROC) analysis. Fifty-five patients with colorectal cancer underwent contrast-enhanced CT colonography using an 8- or 16-row scanner. Two separate interval reviews of the axial MDCT datasets with/without MPR images (coronal and sagittal) were performed independently by two radiologists blinded to both the colonoscopic and histopathologic results. At each review session, the radiologists were asked to determine the colorectal cancer TNM stage within the context of differentiating < or =T3 from T4, N0 from > or =N1 and M0 from M1 using a five-point confidence scale. The radiologists' performance for staging the colorectal cancer using axial CT datasets with/without MPR images was evaluated using ROC analysis. Sensitivities, specificities and interobserver agreement were assessed. When MPR images were added, significant improvement was achieved by both radiologists for differentiating N0 from > or =N1 in terms of both A(Z) (0.651 to 0.769; 0.573 to 0.713) and specificity (26.7 to 69.2%; 23.1 to 76.9%) (P<0.05). For T staging, ROC analysis failed to show a significant improvement in terms of differentiating < or =T3 from T4 for either radiologist (P>0.05), but a significant improvement in the specificity (70 to 90%; 80 to 92%) was achieved by one radiologist (P<0.05). In terms of the M staging, a significant improvement in the Az (0.844 to 0.996) was observed for the combined interpretation of the axial and MPR images by one radiologist (P<0.05). Furthermore, substantial or almost perfect interobserver agreement was achieved for all TNM stagings for the combined interpretations (kappa=0.641-0.866), whereas only fair to substantial agreement was achieved for the axial images alone (kappa=0.337-0.707). In conclusion, the combined interpretation of the axial and MPR MDCT images significantly improved the local staging of colorectal cancer compared with assessments based on axial images alone.

CT colonography features of sigmoid diverticular disease

OBJECTIVE

The objective of this study is to assess the sigmoid distensibility during CT colonography (CTC) in patients with diverticular disease.

METHODS

Consecutive patients without a history of pelvic radiation or neoplasms underwent 150 CTC. Three radiologists in consensus evaluated axial images for colonic distention, luminal diameters (mm), diverticula, and muscular thickening.

RESULTS

The minimum colon diameter in patients with muscular thickening was significantly smaller, irrespective of the presence of diverticula (P=.009).

CONCLUSION

Muscular thickening with diverticular disease was associated with significantly less sigmoid colon distension.

Rectal perforations after barium enema: a review

PURPOSE

Rectal injuries during barium enema are rare but life-threatening complications. The last review about this subject was published more than ten years ago. In the present review, we present an overview on the subject and especially focus on changes in treatment strategies and developments of less risky visualization techniques.

METHODS

A literature search was performed in the PubMed library using the key words-barium enema, complications, peritonitis, and rectal perforation-as well as related articles and other references obtained from these articles.

RESULTS

The most frequent cause of perforation is iatrogenic and catheter-related. Other causes are related to weakness of the colorectal wall or obstruction. Five types of perforations have been described: 1) perforations of the anal canal below the levator; 2) incomplete perforations; 3) perforations into the retroperitoneum; 4) transmural perforations into adjacent viscera; 5) perforations into the free intraperitoneal cavity. Most incomplete perforations and one-half of the retroperitoneal perforations have minimal clinical signs. Intraperitoneal perforations lead to the most catastrophic course, starting with rectal bleeding and mild abdominal complaints. This is rapidly followed by progressive sepsis and peritonitis, and leads to a high mortality rate. Surgery is not always required for intramural or small retroperitoneal perforations. These can be treated conservatively and require surgical debridement only in case of large amounts of extravasation or abscesses. Surgical repair of large rectal mucosal lesions or anal sphincter lesions is advised. Perirectal abscesses require drainage. Intraperitoneal perforations with gross extravasation need immediate aggressive surgical treatment in a critical care setting, because the threat of shock is high. Intraperitoneal perforations, neglected perforations, gross barium extravasation, poorly prepared colon, and venous intravasation of barium are prognostically unfavorable. The severest late complication in intraperitoneal perforations is ileus. Meticulous technical performance of the barium enema is the most important factor in prevention.

CONCLUSIONS

Rectal perforations after barium enema are rare. The overall mortality rate decreased in recent decades from approximately 50 to 35 percent as the result of advances in supportive and intensive care. Because of these advances, more aggressive surgical strategies were undertaken. With the advent of endoscopy, less barium enemas are performed. Consequently, the absolute incidence of complications has decreased. It is expected that in the future barium enemas will be replaced by more sensitive and less risky techniques, such as CT colonography and magnetic resonance colonography.

CT colonography in the detection of colorectal polyps and cancer: systematic review, meta-analysis, and proposed minimum data set for study level reporting

PURPOSE

To assess the methodologic quality of available data in published reports of computed tomographic (CT) colonography by performing systematic review and meta-analysis.

MATERIALS AND METHODS

The MEDLINE database was searched for colonography reports published between 1994 and 2003, without language restriction. The terms colonography, colography, CT colonoscopy, CT pneumocolon, virtual colonoscopy, and virtual endoscopy were used. Studies were selected if the focus was detection of colorectal polyps verified with within-subject reference colonoscopy by using key methodologic criteria based on information presented at the Fourth International Symposium on Virtual Colonoscopy (Boston, Mass). Two reviewers independently abstracted methodologic characteristics. Per-patient and per-polyp detection rates were extracted, and authors were contacted, when necessary. Per-patient sensitivity and specificity were calculated for different lesion size categories, and Forest plots were produced. Meta-analysis of paired sensitivity and specificity was conducted by using a hierarchical model that enabled estimation of summary receiver operating characteristic curves allowing for variation in diagnostic threshold, and the average operating point was calculated. Per-polyp sensitivity was also calculated.

RESULTS

Of 1398 studies considered for inclusion, 24 met our criteria. There were 4181 patients with a study prevalence of abnormality of 15%-72%. Meta-analysis of 2610 patients, 206 of whom had large polyps, showed high per-patient average sensitivity (93%; 95% confidence interval [CI]: 73%, 98%) and specificity (97%; 95% CI: 95%, 99%) for colonography; sensitivity and specificity decreased to 86% (95% CI: 75%, 93%) and 86% (95% CI: 76%, 93%), respectively, when the threshold was lowered to include medium polyps. When polyps of all sizes were included, studies were too heterogeneous in sensitivity (range, 45%-97%) and specificity (range, 26%-97%) to allow meaningful meta-analysis. Of 150 cancers, 144 were detected (sensitivity, 95.9%; 95% CI: 91.4%, 98.5%). Data reporting was frequently incomplete, with no generally accepted format.

CONCLUSION

CT colonography seems sufficiently sensitive and specific in the detection of large and medium polyps; it is especially sensitive in the detection of symptomatic cancer. Studies are poorly reported, however, and the authors propose a minimum data set for study reporting.

CT colonography: where have we been and where are we going?

Over the past decade, computed tomographic (CT) colonography (also known as virtual colonoscopy) has been used to investigate the colon for colorectal neoplasia. Numerous clinical and technical advances have allowed CT colonography to advance slowly from a research tool to a viable option for colorectal cancer screening. However, substantial controversy remains among radiologists, gastroenterologists, and other clinicians with regard to the current role of CT colonography in clinical practice. On the one hand, all agree there is much excitement about a noninvasive imaging examination that can reliably depict clinically important colorectal lesions. However, this is tempered by results from several recent studies that show the sensitivity of CT colonography may not be as great when performed and the images interpreted by radiologists without expertise and training. The potential to miss important lesions exists; moreover, if polyps cannot be differentiated from folds and residual fecal matter, unnecessary colonoscopy will be performed. In this review, current issues will be discussed regarding colon cancer and the established and reimbursed strategies to screen for it and the past, current, and potential future role of CT colonography.

The role of CT colonography in colorectal cancer screening

Computed tomographic colonography (CTC) is a relatively noninvasive technique for large bowel imaging that has the ability to detect colorectal neoplasia. Already well established as a reliable diagnostic tool in symptomatic patients who are unable to undergo complete colonoscopy, it is now being considered as a viable method for population screening. Advances in technique over the past 10 yr make this an attractive alternative, including reduced bowel preparation and stool tagging, three-dimensional (3D) image reconstruction, computer-aided detection software, and low-radiation dose protocols. CTC may be favored by patients compared to other available screening tests due to the ease of performance and comfort. Although published studies vary in relation to the sensitivity of this test for the detection of polyps, in the best hands a sensitivity of greater than 90% for detection of polyps at least 10 mm in diameter may be obtained. Although not yet endorsed for widespread use by major gastroenterological societies, CTC shows promise as a screening tool.

Virtual colonoscopy: current status and future directions

Virtual colonoscopy (CT colonography) is a technique whereby CT images of the cleansed and distended colon are acquired, ostensibly for detecting colonic neoplasia, although also providing additional diagnostic information from extracolonic organs. This article examines the current status of virtual colonoscopy, reviewing the technical parameters, performance characteristics, and issues surrounding implementation in routine clinical practice. Future directions for virtual colonoscopy are explored, including advances toward prepless examinations and automated interpretation.

Low-dose CT colonography in children: initial experience, technical feasibility, and utility

BACKGROUND

CT colonography (CTC) is utilized as a diagnostic tool in the detection of colon polyps and early colorectal cancer in adults. Large studies in the literature, although focused on adult populations, have shown CTC to be a safe, accurate, non-invasive technique.

OBJECTIVE

We evaluated the technical feasibility of CTC in children using a low-dose technique.

MATERIALS AND METHODS

From November 2001 to April 2004 we evaluated eight patients (3-17 years) with non-contrast CTC. Seven of the patients had CTC, followed by standard colonoscopy (SC) the same day; in one patient, CTC followed a failed SC. CTC results were compared to results of SC. The estimated effective dose from each CTC was calculated and compared to that of standard barium enema.

RESULTS

CTC results were consistent with those of SC. Sensitivity for polyps 5-10 mm was 100%, and sensitivity for polyps 10 mm and larger was 66.7%. The estimated mean effective dose was 2.17 mSv for CTC, compared to the 5-6 mSv for a standard air-contrast barium enema in a small child.

CONCLUSION

Our initial experience shows CTC in children is well-tolerated, safe, and useful. The procedure can be performed successfully with a low radiation dose, and preliminary results compare well with SC.

CT colonography with fecal tagging after incomplete colonoscopy

The objective of this study was to evaluate dietary fecal tagging (FT) as a cleansing method prior to CT colonography (CTC) in patients with incomplete conventional colonoscopy (CC). After written informed consent was obtained, 24 patients had standard colonoscopic preparation (ScCl), and 25 patients had FT as cleansing method. Segmental distention, fluid levels, fecal residues, tagged appearance of fluid levels, and residual stool were evaluated. Mann-Whitney U test was used to test for significant differences between FT and ScCl groups. Compared with ScCl, FT improved distention (p=0.001), reduced the amount of fluid (p=0.043), but suffered from residual stool (p=0.046). A clear correlation was found between distention and fluid. No differences were found in stool size between FT and ScCl. FT showed a good labeling of fecal residues, and acceptable labeling of fluid levels. Compared with ScCl, FT reduces fluid, favors distention, but suffers from fecal residues. The tagged nature of these residues, however, allows differentiation from polyps.

The emerging role of virtual colonoscopy

A review of the current status of virtual colonoscopy is germane and topical. Clinicians need to be knowledgeable about this rapidly evolving and clinically relevant technology to understand the test benefits and limitations and to refer patients for this test appropriately. A critical review of the exponentially expanding literature on this subject is important. This article describes the imaging meth-ods, adjunctive techniques, and radiologic interpretation of CT colonography, and comprehensively and critically reviews the clinical data to help the clinician evaluate the current and potential applications of this technology.

MR colonography in patients with incomplete conventional colonoscopy

PURPOSE

To assess dark-lumen magnetic resonance (MR) colonography for the evaluation of colonic segments in patients in whom conventional colonoscopy could not be completed.

MATERIALS AND METHODS

Institutional review board approval and written informed consent were obtained. Within 24 hours of incomplete conventional colonoscopy, 37 patients (22 women, 15 men; age range, 25-63 years) underwent MR colonography. Contrast material-enhanced T1-weighted three-dimensional images were collected after rectal administration of water for colonic distention. Data from MR colonography were evaluated by two radiologists. With a three-point scale, image quality was characterized in terms of colonic distention (1 = good; 2 = moderate, diagnostic; and 3 = poor, nondiagnostic) and presence of artifacts (1 = none; 2 = moderate, diagnostic; and 3 = extensive, nondiagnostic). Depiction of colorectal disease was assessed according to the following colonic segments: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.

RESULTS

Four patients had history of colorectal cancer, and each had undergone partial colonic resection of two segments. Hence, 214 segments were evaluated. Conventional colonoscopy failed in assessment of 127 of 214 potentially visible colonic segments in the 37 patients. MR image quality was rated diagnostic in 35 patients and permitted assessment of 206 of 214 potentially visible segments. Nondiagnostic image quality in two patients was attributed to inadequate distention of prestenotic colonic segments owing to high-grade tumor stenosis. All inflammation- and tumor-induced stenoses and all five polyps identified at conventional colonoscopy in poststenotic segments were correctly detected at MR colonography. However, MR-based assessment of prestenotic segments revealed two lesions suspected of being carcinoma, five polyps, and four segments affected by colitis.

CONCLUSION

MR colonography proved reliable in evaluating the majority of colonic segments inaccessible with conventional colonoscopy. The identification of additional disease at MR colonography underscores the need for a second diagnostic step in the setting of incomplete conventional colonoscopy.

Added value of CT colonography after a positive conventional colonoscopy: impact on treatment strategy

BACKGROUND

Conventional colonoscopy (CC) requires an experienced operator to avoid technical or interpretative errors, and an endoscopic error rate of 14% for tumor localization has been reported. We evaluated the impact of computed tomographic colonography (CTC) on surgical treatment strategy in patients with CC reported as having colorectal neoplasm.

METHODS

Fifty-three patients testing positive for colorectal neoplasm on CC underwent CTC: 32 patients had CC in our hospital (group A) and 21 had CC in area hospitals (group B). All CTC procedures were performed with a multidetector CT system. The results of CTC and CC were compared with that of surgery. The preoperative surgical planning evaluated on the basis of CC and CTC was compared with the actual surgical approach, and the percentage of patients in whom CTC modified the treatment strategy suggested by CC was calculated.

RESULTS

CTC changed the treatment strategy in four of 53 patients (7.5%) in whom CC showed technical or interpretative errors. Group analysis showed that CTC did not influence the surgical management in any patient in group A but did affect treatment strategy in four of 21 patients (19%) in group B. The effect of CTC on treatment strategy between groups was statistically significant (p < 0.05). CTC identified five adenomas and three adenocarcinomas localized proximally to an impassable stenosis.

CONCLUSION

CTC can be used to reevaluate the findings of a positive CC and can indicate a more correct therapeutic approach in patients with colorectal neoplasms who are candidates for surgery.

Early experiences with computed axial tomography colonography

BACKGROUND

Computed axial tomography (CT) colonography is the latest radiologic technique to be used to image the large bowel. We studied its role as a diagnostic tool in colorectal practice.

METHODS

One hundred and three patients suspected of having colorectal pathology underwent CT colonography.

RESULTS

CT colonography suggested a diagnosis of colonic carcinoma in 18 patients, and 17 of these underwent surgery. A colorectal neoplasm was not found in only 1 patient who had extrinsic colonic compression by an ovarian cyst. Twenty-one patients had suspected colonic polyps on scanning. Subsequent endoscopy in 19 of these patients confirmed the presence of polyps in only 10. CT colonography also revealed valuable extracolonic pathology: 8 occult noncolonic neoplasms and 163 other incidental findings.

CONCLUSIONS

CT colonography has good patient compliance and is a useful diagnostic modality in detecting colorectal neoplasms. Its main advantage over other such investigative tools is its ability to detect extracolonic pathology.

Computed Tomographic Colonography (CTC): Possibilities and Limitations of Clinical Application in Colorectal Polyps and Cancer

Colorectal cancer is the second leading cause of cancer-related deaths in Europe and the United States. Most colorectal cancers develop from adenomatous polyps over a number of years. Early detection of polyps eliminates the risk of subsequent carcinomas.

Computed tomographic (CT) colonography is a diagnostic technique detecting colorectal neoplasms. With the introduction of multidetector-row computed tomography (MD-CT), CT colonography (CTC) has gained influence as a new diagnostic tool in early detection of colonic pathologies by acquiring volumetric CT data sets of the abdomen. This volumetric data is analyzed using CTC workstations, which provide an interactive display of 2D and 3D images of the colon. In several studies, CTC revealed a high accuracy (sensitivity/patient: 83–100% and specificity/patient: 93–100%) in detecting pathological colonic changes. Furthermore, CTC is an excellent diagnostic technique for the evaluation of patients with incomplete conventional colonoscopy and allows the assessment of extracolonic abdominal and pelvic organs.

In this article, the status of CT colonography as a method of detecting colonic polyps and colorectal carcinomas using single- and multidetector-row CT will be reviewed.

Comparison of the relative sensitivity of CT colonography and double-contrast barium enema for screen detection of colorectal polyps

BACKGROUND & AIMS

In a population reflective of a screening setting, our aim was to compare the relative sensitivity and specificity of computed tomography (CT) colonography with double-contrast barium enema (DCBE) for detection of colorectal polyps and to assess the added value of double reading at CT colonography, using endoscopy as the arbiter.

METHODS

This prospective, blinded study comprised 837 asymptomatic persons at higher than average risk for colorectal cancer who underwent CT colonography followed by same-day DCBE. Examinations with polyps > or =5 mm in diameter were referred to colonoscopy.

RESULTS

CT colonography readers detected 56%-79% of polyps > or =10 mm in diameter. In comparison, the sensitivity at DCBE varied between 39% and 56% for the 31 polyps > or =1 cm. All of the readers detected more polyps at CT colonography than DCBE, but the difference was statistically significant for only a single reader (P = 0.02). Relative specificity for polyps > or =10 mm on a per-patient basis ranged from 96% to 99% at CT colonography, and 99%-100% at DCBE. Doubly read CT colonography detected significantly more polyps than DCBE (81% vs. 45% for polyps > or =1 cm [P = <0.01], and 72% vs. 44% for polyps 5-9 mm [P < or = 0.01]).

CONCLUSIONS

Double-read CT colonography is significantly more sensitive in detecting polyps than single-read double contrast barium enema. DCBE was significantly more specific than CT colonography.

Colorectal polyps and cancers in asymptomatic average-risk patients: evaluation with CT colonography

PURPOSE

To compare thin-section multi-detector row computed tomographic (CT) colonography with conventional colonoscopy in the evaluation of colorectal polyps and cancer in asymptomatic average-risk patients.

MATERIALS AND METHODS

Sixty-eight asymptomatic men (age > 50 years) scheduled to undergo screening colonoscopy were enrolled in this study. CT colonography was followed by conventional colonoscopy, performed on the same day. Supine and prone CT colonography were performed after colonic insufflation with room air. A gastroenterologist measured all polyps, which were categorized as 1-5, 6-9, or over 10 mm. Biopsy and histologic evaluation were performed of all polyps. CT colonography and colonoscopy results were compared for location, size, and morphology of detected lesions. Point estimates and 95% CIs were provided for specificity and sensitivity of CT by using results at conventional colonoscopy as the reference standard.

RESULTS

At colonoscopy, 98 polyps were identified in 39 patients; 21 (21.4%) of 98 were detected at CT colonography. Sensitivity was 11.5% (nine of 78) for polyps 1-5 mm, 52.9% (nine of 17) for polyps 6-9 mm, and 100% (three of three) for polyps over 10 mm. Results at colonoscopy were normal in 29 (42.6%) of 68 patients; at CT colonography, results were correctly identified as normal in 26 of these 29 patients. In one of these patients, a lesion larger than 10 mm was detected at CT colonography. The per-patient specificity of CT was 89.7% (26 of 29; 95% CI: 72.7%, 97.8%). The mean time for CT image interpretation was 9 minutes.

CONCLUSION

In patients at average risk for colorectal cancer, CT colonography is a sensitive and specific screening test for detecting polyps 10 mm or larger; the sensitivity for detecting smaller polyps is decreased. Examination findings can be interpreted in a clinically feasible amount of time.

Detection of colorectal lesions: lower-dose multi-detector row helical CT colonography compared with conventional colonoscopy

PURPOSE

To compare the performance of lower-dose multi-detector row helical computed tomographic (CT) colonography with that of conventional colonoscopy in the detection of colorectal lesions.

MATERIALS AND METHODS

One hundred fifty-eight patients underwent multi-detector row helical CT colonography (beam collimation, 4 x 2.5 mm; table feed, 17.5 mm/sec; voltage, 140 kV; and effective dose, 10 mAs) followed by conventional colonoscopy. Conventional colonoscopy served as the reference standard. Two radiologists interpreted CT colonographic images to assess the presence of polyps or carcinomas. Sensitivity was calculated on both a per-polyp and a per-patient basis. In the latter, specificity and positive and negative predictive values were also calculated. Weighted CT dose index was calculated on the basis of measurements obtained in a standard body phantom. Effective dose was estimated by using commercially available software.

RESULTS

CT colonography correctly depicted all 22 carcinomas (sensitivity, 100%) and 52 of 74 polyps (sensitivity, 70.3%). Sensitivity for detection was 100% in all 13 polyps 10 mm or larger in diameter, 83.3% in 20 of 24 polyps 6-9 mm, and 51.3% in 19 of 37 lesions 5 mm or smaller. With regard to the per-patient analysis, CT colonography had a sensitivity of 96.0%, a specificity of 96.6%, a positive predictive value of 94.1%, and a negative predictive value of 97.7%. The total weighted CT dose index for combined prone and supine acquisitions was 2.74 mGy. The simulated effective doses for complete CT colonography were 1.8 mSv in men and 2.4 mSv in women.

CONCLUSION

Lower-dose multi-detector row helical CT colonography ensures substantial dose reduction while maintaining excellent sensitivity for detection of colorectal carcinomas and polyps larger than 6 mm in diameter.

CT colonography practice in the UK: a national survey

AIM

To determine the provision of computed tomography (CT) colonography in UK radiology departments.

MATERIALS AND METHODS

A questionnaire relating to the availability of CT colonography, barriers to implementation, clinical indications, technique, and practitioners was posted to clinical directors of UK radiology departments.

RESULTS

One hundred and thirty-eight departments responded. Fifty (36%) offered CT colonography in day-to-day clinical practice. Of those that did not, 68 of 87 (64%) cited limited scanner capacity as the main barrier. Of the 50 departments offering a service, 39 (78%) offered CT after incomplete colonoscopy, 36 (72%), after failed barium enema, and 37 (74%) as an alternative to barium enema. Of those offering a service, the number of studies performed varied between one per month (38%) to more than one per day (8%). Total experience varied between 20 or fewer studies (28%) to more than 300 (12%). Full bowel preparation was common (92%), as was dual positioning (90%). Colonography was interpreted by radiologists with a subspecialty interest in gastrointestinal imaging in 64% of centres offering a service.

CONCLUSION

CT colonography is widely available in the UK, with approximately one-third of responders offering a service. Experience and throughput varies considerably. Limited CT scanner capacity is the major barrier to further dissemination.

Use of multidetector-row CT colonography for detection of colorectal neoplasia in patients referred via the Department of Health "2-Week-wait" initiative

AIM

Patients referred under the Department of Health 2-week wait initiative with symptoms of colorectal cancer frequently undergo whole-colon examination. We investigated the use of computed tomography (CT) colonography as an alternative to colonoscopy in this scenario.

MATERIALS AND METHODS

Fifty-four consecutive patients, referred via the 2-week wait initiative and scheduled for colonoscopy, consented to undergo multidetector CT colonography immediately before endoscopy. The site and morphology of any polyp or cancer detected by CT was noted and comparison made with subsequent colonoscopy.

RESULTS

Colonoscopy detected polyps or cancer in 29 patients (53.7%). CT colonography prospectively detected 18 of 41 (44%) polyps of 1-5 mm, three of four (75%) polyps of 6-9 mm, four of four (100%) polyps 10 mm or larger, and five of six (83%) cancers. The missed cancer occurred early in the series and was a perceptive error. The overall sensitivity, specificity, positive predictive value and negative predictive value of CT colonography for cancer and polyps 10 mm or greater on a per patient basis were 90, 100, 100 and 98%, respectively. CT detected one renal cancer and one colonic cancer, initially missed due to incomplete colonoscopy.

CONCLUSION

CT colonography is a robust technique for investigation of symptomatic patients. The learning curve must be overcome for optimal performance.

Computerized tomographic colonography: performance evaluation in a retrospective multicenter setting

BACKGROUND & AIMS

No multicenter study has been reported evaluating the performance and interobserver variability of computerized tomographic colonography. The aim of this study was to assess the accuracy of computerized tomographic colonography for detecting clinically important colorectal neoplasia (polyps >or=10 mm in diameter) in a multi-institutional study.

METHODS

A retrospective study was developed from 341 patients who had computerized tomographic colonography and colonoscopy among 8 medical centers. Colonoscopy and pathology reports provided the standard. A random sample of 117 patients, stratified by criterion standard, was requested. Ninety-three patients were included (47% with polyps >or=10 mm; mean age, 62 years; 56% men; 84% white; 40% reported colorectal symptoms; 74% at increased risk for colorectal cancer). Eighteen radiologists blinded to the criterion standard interpreted computerized tomography colonography examinations, each using 2 of 3 different software display platforms.

RESULTS

The average area under the receiver operating characteristic curve for identifying patients with at least 1 lesion >or=10 mm was 0.80 (95% lower confidence bound, 0.74). The average sensitivity and specificity were 75% (95% lower confidence bound, 68%) and 73% (95% lower confidence bound, 66%), respectively. Per-polyp sensitivity was 75%. A trend was observed for better performance with more observer experience. There was no difference in performance across software display platforms.

CONCLUSIONS

Computerized tomographic colonography performance compared favorably with reported performance of fecal occult blood testing, flexible sigmoidoscopy, and barium enema. A prospective study evaluating the performance of computerized tomography colonography in a screening population is indicated.

Preoperative staging of colorectal cancer--computed tomography and magnetic resonance imaging

Cross-sectional imaging techniques are increasingly being used in the preoperative evaluation of patients with colorectal cancer. Both computed tomography (CT) and magnetic resonance (MR) imaging have been improved with significant advances of the technological hard- and software. This has contributed to high patient acceptance due to shorter examination times and more open configuration of the systems, consistent high quality images with better delineation of the normal abdomino-pelvic anatomy and pathology. New techniques such as CT-colonography have emerged from a research application to a clinical tool which can be used in different clinical settings. Phased-array receiver coils have significantly increased the usefulness of MR in the evaluation of rectal neoplasms due to the high resolution that can be obtained. New organ specific contrast agents for magnetic resonance imaging have facilitated the preoperative evaluation of liver metastases in favour of more invasive techniques with similar sensitivities. However, preoperative staging criteria for colorectal cancer using computed tomography and magnetic resonance imaging has to be updated and the results of new techniques have to be confirmed in large trials. In the future, further development of CT and MR may offer 'one-stop-shopping' protocols for both diagnosis, local and distant staging of colorectal cancer. Diffusion weighted MR-imaging, in vivo spectroscopy as well as further targeted imaging, such as with lymph node specific agents for MR may also prove to be helpful in the preoperative evaluation of patients with colorectal cancer.

Prospective blinded evaluation of computed tomographic colonography for screen detection of colorectal polyps

BACKGROUND & AIMS

This study used a low lesion prevalence population reflective of the screening setting to estimate the sensitivity and specificity of computerized tomographic (CT) colonography for detection of colorectal polyps.

METHODS

This prospective, blinded study comprised 703 asymptomatic persons at higher-than-average risk for colorectal cancer who underwent CT colonography followed by same-day colonoscopy. Two of 3 experienced readers interpreted each CT colonography examination.

RESULTS

Overall lesion prevalence for adenomas >/=1 cm in diameter was 5%. Seventy percent of all lesions were proximal to the descending colon. With colonoscopy serving as the gold standard, CT colonography detected 34%, 32%, 73%, and 63% of the 59 polyps >/=1 cm for readers 1, 2, 3, and double-reading, respectively; and 35%, 29%, 57%, and 54% of the 94 polyps 5-9 mm for readers 1, 2, 3, and double-reading, respectively. Specificity for CT colonography ranged from 95% to 98% and 86% to 95% for >1 cm and 5-9-mm polyps, respectively. Interobserver variability was high for CT colonography with kappa statistic values ranging from -0.67 to 0.89.

CONCLUSIONS

In a low prevalence setting, polyp detection rates at CT colonography are well below those at colonoscopy. These rates are less than previous reports based largely on high lesion prevalence cohorts. High interobserver variability warrants further investigation but may be due to the low prevalence of polyps in this cohort and the high impact on total sensitivity of each missed polyp. Specificity, based on large numbers, is high and exhibits excellent agreement among observers.

Feasibility study of using air as a contrast medium in MR colonography

AIM

To evaluate the feasibility of using air as intraluminal contrast medium in magnetic resonance (MR) colonography.

MATERIALS AND METHODS

Twenty-two patients underwent MR colonography (MRC) using air before colonoscopy. All patients were imaged in prone and supine positions. Each colon was divided into five segments. Two radiologists reviewed the images for the degree of colonic distension, image quality and colonic lesions. The colonic lesions identified using MR were compared with those identified on colonoscopy.

RESULTS

Eight men and 14 women with mean age of 55.5 years were studied. All patients completed the MR examination. One hundred and five out of 110 (95.5%) colonic segments were well distended in both prone and supine positions. Image quality was good in all cases. Colonoscopy detected 16 lesions: three > or = 1 cm, one 7 mm lesion and 12 lesions < or = 5 mm. All lesions 1 cm or larger were detected by MRC.

CONCLUSION

MRC using air and the single-shot half-Fourier rapid acquisition with refocused echoes (RARE) technique is feasible. But in this small pilot study, it had low sensitivity for the detection of polyps less than 1 cm in diameter.

CT colonography: methods, pathology and pitfalls

Computed tomography colonography (CTC) is a relatively new technique that is currently challenging more established methods of large bowel imaging. Several workers have suggested CTC surpasses the barium enema and approaches conventional endoscopy for detection of colorectal neoplasia. Accurate diagnosis relies on technically good studies, the main aim of which is adequate bowel cleansing and distension. Furthermore, the learning curve is steep and normal colonic anatomy has to be re-learned in a CT context. This review aims to describe the technique, revise the imaging features of both normal and pathological colon, and to highlight potential diagnostic pitfalls and their avoidance.

Virtual colonoscopy. Potential clinical applications of a new technique

The potential role of virtual colonoscopy is not limited to colorectal cancer screening, although that is its greatest potential. Same-day VC should be offered for patients undergoing an incomplete colonoscopy. Conversely, faster, more accurate interpretation by the radiologist on the same day as a VC should lead to the consideration by the gastroenterologist of same-day colonoscopy for patients with a suspicious, significantly sized polyp.

Virtual endoscopy

Virtual endoscopy is a new-generation technique which combines the features of endoscopic viewing and cross-sectional volumetric imaging. In the evaluation of gastrointestinal cancers, virtual endoscopy has been most commonly used in colorectal carcinomas and to a much lesser extent in gastric carcinomas. In this review, the current status of virtual colonoscopy was reviewed together with a brief discussion of virtual gastroscopy.

Colorectal cancer: role of CT colonography in preoperative evaluation after incomplete colonoscopy

PURPOSE

To evaluate computed tomographic (CT) colonography in patients with clinical suspicion of colorectal cancer and in whom colonoscopy was incomplete.

MATERIALS AND METHODS

After incomplete colonoscopy, 34 patients underwent CT colonography before and after intravenous injection of iodinated contrast agent, in supine and prone positions. Twenty patients with no evidence of colon cancer after complete colonoscopy were included as a control group. Sensitivity and specificity of CT colonography were determined for detection of cancers, polyps, and metastases to liver.

RESULTS

In 29 patients, surgery revealed 30 colorectal cancers (three synchronous cancers) and two ischemic lesions of the descending colon. Colonoscopy missed 10 colorectal cancers and three synchronous cancers; all were detected with CT colonography. Sensitivity and specificity for detection of colorectal cancer were 56% and 92%, respectively, for incomplete colonoscopy and 100% and 96%, respectively, for CT colonography (P <.01). Sensitivity and specificity of CT colonography in detection of polyps were 86% and 70%, respectively, for diameters of 5 mm or less; 100% and 80%, respectively, for 5-10-mm diameters; and 100% for diameters greater than 10 mm. Spiral CT of the liver revealed four metastases (2-5 cm); sensitivity and specificity were 100% and 43% for nonenhanced scans and 100% for contrast-enhanced scans (P <.01).

CONCLUSION

In this selected group of patients, CT colonography provided complete information to properly address surgery of colorectal cancer and treatment of liver metastases.

Diagnostic yield of barium enema examination after incomplete colonoscopy

PURPOSE

To determine the diagnostic yield of barium enema examination for neoplastic lesions larger than 1 cm in diameter in the nonvisualized portion of the colon after incomplete colonoscopy.

MATERIALS AND METHODS

A review of computerized gastroenterology and radiology databases identified 355 patients who underwent incomplete colonoscopy; 158 (44.5%) underwent subsequent barium enema examination (125 double-contrast and 33 single-contrast barium enema examinations). The radiographic reports were reviewed and compared with the endoscopic reports by one author to identify neoplastic lesions larger than 1 cm in the nonvisualized colon after incomplete colonoscopy. Six such lesions were found. In all six cases, the images from the barium enema examinations were reviewed together by two authors to determine the size, location, and morphologic features (polypoid, ulcerated, or annular) of the lesions. Medical, endoscopic, and surgical records were subsequently reviewed by one author to determine whether these represented true- or false-positive radiographic findings.

RESULTS

Barium enema examination depicted six possible lesions in the nonvisualized colon after incomplete colonoscopy; five were found to be true-positive radiographic findings, and one was found to be a false-positive finding. The five true-positive findings included two annular lesions (both adenocarcinomas) and three polypoid lesions (all tubulovillous adenomas, with high-grade dysplasia in one). Thus, neoplastic lesions larger than 1 cm were found on barium enema images in the nonvisualized colon in five (3.2%) of 158 patients after incomplete colonoscopy.

CONCLUSION

Barium enema examination had a diagnostic yield of 3.2% for neoplastic lesions larger than 1 cm in the nonvisualized colon after incomplete colonoscopy.

Quality of virtual colonoscopy in patients who have undergone radiation therapy or surgery: how successful are we?

OBJECTIVE

In patients who have a history of abdominopelvic radiation, surgery, or both, conventional colonoscopy may fail to examine the entire colon. The purpose of this study is to assess whether high-quality virtual colonoscopy can be achieved in this patient population.

MATERIALS AND METHODS

After colonic cleansing, 61 patients (16 men and 45 women; mean age, 64 years; age range, 27-81 years) underwent 63 virtual colonoscopy examinations after using either single- or multidetector CT (slice thickness, 3.75-5.0 mm; table speed, 1.7-11.25 cm/sec; pitch, 1.5-3.0; and overlapped reconstructions, 1.95-2.5 cm) in supine and prone positions after IV administration of 1 mg of glucagon and rectal air insufflation. Conventional two-dimensional axial images were analyzed on a PACS (picture archiving and communication system) workstation. Two radiologists, who were unaware of patient history, independently evaluated the colonic distention on a 4-point scale (4 = optimal distention) and fluid retention on a 3-point scale (3 = no fluid) for all segments of the colon in patients who were imaged in both the supine and prone positions. Segmental and total average colon scores were calculated.

RESULTS

Forty-one patients (65%; 43 examinations, 67%) underwent prior surgery, radiation, or both (surgery, n = 29; radiation, n = 3; both, n = 11). The average overall colonic distention and fluid retention for this group was 3.13 and 2.38, respectively, versus 3.24 and 2.3 in the control group (p = not significant).

CONCLUSION

High-quality examinations were achieved in patients who had previously undergone radiation, surgery, or both with no clinically significant difference in distention or fluid retention compared with the controls.

Radiology of colorectal cancer

In the past 20 years, the radiology of colorectal cancer has evolved from the barium enema to advanced imaging modalities like phased array magnetic resonance imaging (MRI), virtual colonoscopy and positron emission tomography (PET). Nowadays, primary rectal cancers are preferably imaged with transrectal ultrasound or MRI, while barium enema is still the most often used technique for imaging of colonic cancers. Virtual colonoscopy is rapidly evolving and might considerably change the imaging of colorectal cancer in the near future. The use of virtual colonoscopy for screening purposes and imaging of the colon in occlusive cancer or incomplete colonoscopies is currently under evaluation. The main role of PET is in detecting tumour recurrences, both locally and distantly. Techniques to fuse cross-sectional anatomical (computer tomography (CT) and MRI) and functional (PET) images are being developed. Apart from diagnostic imaging, the radiologists has added image-guided minimally invasive treatments of colorectal liver metastases to their arsenal. The radio-frequency ablation technique is now widely available, and can be used during laparotomy or percutaneously in selected cases.

Virtual colonoscopy

Computerized tomographic colonography (CT colonography) is a new, non-invasive technique that has been developed over the last few years; it looks at the large bowel in detail. In this chapter we look at how the examination is performed and we consider how the images are displayed. We describe the normal features of the colon, as seen using this technique, as well as the features of common pathological conditions. We will discuss screening for colorectal cancer and the performance of CT colonography; we compare the latter with other procedures currently employed in the screening and diagnosis of colorectal pathology. We consider the difficulties in interpreting these CT colonographic images and look at ways to overcome such difficulties. Finally we discuss future developments of this exciting, new technique.

Computed tomography colonography (virtual colonoscopy): review

Computed tomography examination of the colon performed after bowel cleansing and distension of the lumen with gas goes by several different names--CT colonography (CTC) and CT colography perhaps being the most common. Strictly, the term 'virtual colonoscopy' (VC), should be reserved for the process of examining 3-D, simulated endoluminal images with a capability to navigate through the bowel using appropriate software. Computed tomography colonography appears to be the name that has gained favour among radiologists, although it is suspected that 'virtual colonoscopy' will persist as a generic term due to its attractive 'high-tech' connotations for non-radiological medical and lay persons. Whatever the name, the technique has been made possible through the advent of fast helical CT scanners which allow acquisition of a volume of data, and of proprietary software which enables multiplanar reformatting and 3-D endoluminal reconstructions. It is evident that if CTC/VC can be shown to be acceptable to patients, safe, affordable and accurate, it has enormous potential as a diagnostic and screening tool for colorectal neoplasia.

Detection of colorectal lesions with virtual computed tomographic colonography

BACKGROUND

The aim of our study was to compare the performance of virtual computed tomographic colonography with that of conventional colonoscopy in a blinded, prospective study in 165 patients with suspected colorectal lesions.

METHODS

There were 165 patients, all referred for conventional colonoscopy, who underwent preliminary virtual computed tomographic colonography. Computed tomograhic images of all suspected lesions were analyzed and subsequently compared with conventional colonoscopy findings.

RESULTS

There were 30 colorectal cancers and 37 polyps identified at conventional colonoscopy. Virtual computed tomographic colonography correctly detected all cancers, as well as 11 of 12 polyps of 10 mm in diameter or larger (sensitivity, 92%); 14 of 17 polyps between 6 and 9 mm (sensitivity, 82%); and 4 of 8 polyps of 5 mm or smaller (sensitivity, 50%). The per-patient sensitivity and specificity were 92% and 97%, respectively.

CONCLUSIONS

Virtual computed tomographic colonography has a diagnostic sensitivity similar to that of conventional colonoscopy for the detection of colorectal lesions larger than 6 mm in diameter.

Patient acceptance of CT colonography and conventional colonoscopy: prospective comparative study in patients with or suspected of having colorectal disease

PURPOSE

To prospectively evaluate, by means of self-assessed questionnaires, patient acceptance of computed tomographic (CT) colonography compared with that of conventional colonoscopy, when performed in patients with or suspected of having colorectal disease.

MATERIALS AND METHODS

One hundred eleven patients underwent CT colonography followed immediately by conventional colonoscopy. Patient acceptance was evaluated with questionnaires, and the proportions of patients who favored one examination were compared. The main variables were overall impression, discomfort during air filling or instrumentation, and perceived pain, evaluated by using ordered verbal descriptor scales after each examination. The preference for either examination was evaluated after completion of both examinations.

RESULTS

Of the 68 patients who favored one examination, 56 (82%) preferred CT colonography (P <.00001). Concerning overall impression of problems or discomfort in connection with the examination, 49 (69%) of 71 with a preference considered colonoscopy to be more difficult (P =.002). CT colonography was regarded as "not painful" by 62 (57%) of 108 patients compared with 28 (26%) for colonoscopy, and a larger proportion of patients rated pain as higher during colonoscopy than during CT colonography (95% CI: 30%, 56%). Discomfort from air filling of the colon was the major complaint about CT colonography.

CONCLUSION

CT colonography was considered less painful and less difficult overall than colonoscopy and was the preferred examination.

Colon cancer screening with virtual colonoscopy: promise, polyps, politics

Virtual colonoscopy (CT colonography) promises to become a primary method for colorectal cancer screening and return radiologists to a major role in colon cancer prevention. Results from major centers in the United States show accuracy to be comparable to conventional colonoscopy for detection of polyps of significant size--that is, greater than 10 mm--with few false-positives. The advent of virtual colonoscopy has also heightened awareness of the natural history of colonic polyps, particularly in terms of identifying an appropriate target size for detection in colorectal screening programs. Small polyps (<10 mm) are often either hyperplastic on histology or are unlikely to progress to frank cancer in the patient's lifetime and are therefore of little clinical significance for the average adult. Thus, the rationale for detecting and removing each and every colonic polyp regardless of size has come under increasing scrutiny in the context of cost-benefit analysis of various test strategies for colorectal cancer screening. Virtual colonoscopy may allow patients to obtain reliable information about the status of their colonic mucosa noninvasively and thus make a more informed decision as to whether to proceed to conventional colonoscopy for polypectomy.

Virtual colonoscopy: clinical results

CT colonography is an evolving noninvasive imaging technique that allows detection of colorectal polyps and cancers. When assessing the clinical results of this test, several points need to be emphasized. First, as computed tomography (CT) technology improves, so will clinical results. Therefore, earlier results reporting the accuracy of CT colonography may not be applicable to the current state of the art. Second, as clinical experience has grown, an understanding of the limitations and pitfalls of the technique has increased. A learning curve is involved and, with increased experience, results should improve. This article will focus on the evolving clinical results of CT colonography.

Colon carcinoma: MR imaging with CO2 enema--pilot study

Prior to surgery, seven patients with known colonic tumors underwent breath-hold single-shot fast spin-echo magnetic resonance imaging during a CO2 enema. The images were evaluated for depiction of tumor, adjacent structures, and the remaining colon, and findings were compared with findings at surgery. In all seven patients, the tumor was demonstrated, and in four (57%), breach of the muscularis propria was correctly predicted.