Computed tomographic colonography and conventional colonoscopy for colon diseases: a prospective, blinded study

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.

Colorectal cancer screening and surveillance with CT colonography: current controversies and obstacles

Computed tomographic (CT) colonography has been advocated as an alternative colorectal screening method because studies in populations with a high prevalence of polyps have demonstrated that sensitivity for patients with large (> or =10 mm) polyps is generally high (approximately 90%). In three recent studies in low-prevalence populations, however, these values vary from 55% to 94%. Many questions have been raised as to the cause of this remarkable variability, which hampers the implementation of CT colonography in colorectal cancer screening and surveillance. We provide an overview of some potential causes and discuss the available, often indirect, evidence. In addition, several other obstacles that may influence implementation are discussed. Many differences between the study with high sensitivity (94%) and the two studies with low sensitivity (55% and 64%) exist: the primary method to review the data (two or three dimensional), bowel preparation (with or without oral contrast agents), study design (verification method and analysis of adenomas only), reader's experience, and scanning technique (single vs. multislice, thin vs. thick sections). Additional obstacles for implementation in prevention of colorectal cancer may be controversial results concerning patient acceptance, the large-scale use of ionizing radiation, difficulties in detecting flat adenomas, and extracolonic findings. Use of primary three-dimensional review methods, addition of oral contrast agents to bowel preparation, and endoscopic verification of false-positive results on CT colonography are speculated to have a positive influence on sensitivity. Future investigations should demonstrate the influence of these potential factors on sensitivity of CT colonography. Despite a growing body of evidence, it remains uncertain to what extent patient acceptance, radiation issues, flat lesions, and extracolonic findings will be a stumbling block to using CT colonography for colorectal cancer screening.

Computed tomographic colonography without cathartic preparation for the detection of colorectal polyps

BACKGROUND AND AIMS

We prospectively compared the performance of low-dose multidetector computed tomographic colonography (CTC) without cathartic preparation with that of colonoscopy for the detection of colorectal polyps.

METHODS

A total of 203 patients underwent low-dose CTC without cathartic preparation followed by colonoscopy. Before CTC, fecal tagging was achieved by adding diatrizoate meglumine and diatrizoate sodium to regular meals. No subtraction of tagged feces was performed. Colonoscopy was performed 3-7 days after CTC. Three readers interpreted the CTC examinations separately and independently using a primary 2-dimensional approach using multiplanar reconstructions and 3-dimensional images for further characterization. Colonoscopy with segmental unblinding was used as reference standard. The sensitivity of CTC was calculated both on a per-polyp and a per-patient basis. For the latter, specificity, positive predictive values, and negative predictive values were also calculated.

RESULTS

CTC had an average sensitivity of 95.5% (95% confidence interval [CI], 92.1%-99%) for the identification of colorectal polyps > or =8 mm. With regard to per-patient analysis, CTC yielded an average sensitivity of 89.9% (95% CI, 86%-93.7%), an average specificity of 92.2% (95% CI, 89.5%-94.9%), an average positive predictive value of 88% (95% CI, 83.3%-91.5%), and an average negative predictive value of 93.5% (95% CI, 90.9%-96%). Interobserver agreement was high on a per-polyp basis (kappa statistic range, .61-.74) and high to excellent on a per-patient basis (kappa statistic range, .79-.91).

CONCLUSIONS

Low-dose multidetector CTC without cathartic preparation compares favorably with colonoscopy for the detection of colorectal polyps.

Magnetic resonance imaging based colonography for diagnosis and assessment of diverticulosis and diverticulitis

BACKGROUND AND AIMS

MRI-based colonography is a new minimally invasive imaging modality to assess the colon and abdomen. This new method which is applied mainly for polyp screening could be an integrative approach for colonic diverticulitis assessment. This study evaluated the feasibility of MRI-based colonography to assess diverticulosis or diverticulitis.

PATIENTS AND METHODS

Fourteen consecutive patients with clinically suspected diverticulitis were examined by MRI colonography on a 1.5-T scanner. All patients underwent abdominal CT as gold standard. N-Butyl-scopalamin was given intravenously to reduce bowel peristalsis. After rectal administration of a T1-positive enema T1- and T2-weighted acquisitions with additional intravenous contrast were obtained. A 3D FLASH sequence was acquired for virtual colonography. The results were compared with CT and biological parameters such as white blood cell count and C-reactive protein.

RESULTS

Of 56 bowel segments (sigmoid colon, descending colon, transverse colon, ascending colon) in all 14 patients 54 were assessed to have good to fair image quality. Having CT as standard of reference, all sigmoid diverticula were diagnosed based on MRI. Inflammation as judged by CT was identically assessed on MRI. 3D models of the colon revealed further diverticula in the remaining colon; additionally, the 3D models gave a comprehensive image for surgical planning.

CONCLUSION

In our preliminary study MRI colonography revealed the same diagnosis as CT in all patients without ionizing radiation. Additionally, 3D-rendered models and virtual colonoscopy can be performed. This comprehensive 3D models could replace presurgical planning barium enema with concurrent assessment of the residual colon.

Understanding interpretive errors in radiologists learning computed tomography colonography

RATIONALE AND OBJECTIVES

To determine if interpretive errors in the course of learning CT colonography are secondary to failures in detection or in characterization and determine the types of lesions frequently missed.

MATERIALS AND METHODS

Fifteen radiologists completed an electronic CTC training module consisting of two parts: 1) a teaching file demonstrating the varied appearances of polyps, cancers, and pitfalls in interpreting exams; and 2) a test of 50 complete CTC datasets. Following review of each test case, radiologists were asked to indicate if and where a polyp was visualized. The module then showed each neoplasm (if any) located within the dataset. For false negative examinations, radiologists indicated if the lesion was not seen, was seen but interpreted as colonic wall or fold, or was seen but interpreted as stool or fluid.

RESULTS

The average sensitivity for sessile, pedunculated, and flat polyps for these novice readers was 76%, 63%, and 32%, respectively. Average sensitivity for all morphologies of cancers (annular, polypoid, flat) was high (93%, 85%, 95%), with 8/11 missed cancers being secondary to failure in detection. The most frequently missed cancer was an annular constricting tumor (5/11). Overall, 55% (73/132) of errors were failures of detection and 45% (59/132) were errors in characterization.

CONCLUSION

Radiologists learning CT colonography had slightly more errors of detection than characterization, but this difference was not statistically significant. Flat and pedunculated polyps and annular constricting cancers were the most frequently missed morphologies. Examples of these abnormalities should be emphasized in CTC training programs.

Postprocessing techniques of CT colonography in detection of colorectal carcinoma

AIM: To evaluate the value of postprocessing techniques of CT colonography, including multiplanar reformation (MPR), virtual colonoscopy (VC), shaded surface display (SSD) and Raysum, in detection of colorectal carcinomas.

METHODS: Sixty-four patients with colorectal carcinoma underwent volume scanning with spiral CT. MPR, VC, SSD and Raysum images were obtained by using four kinds of postprocessing techniques in workstation. The results were comparatively analyzed according to circumferential extent, lesion length and pathology pattern of colorectal carcinomas. All diagnoses were proved pathologically and surgically.

RESULTS: The accuracy of circumferential extent of colorectal carcinoma determined by MPR, VC, SSD and Raysum was 100.0%, 82.8%, 79.7% and 79.7%, respectively. There was a significant statistical difference between MPR and VC. The consistent rate of lesion length was 89.1%, 76.6%, 95.3% and 100.0%, respectively. There was a statistical difference between VC and SSD. The accuracy of discriminating pathology pattern was 81.3%, 92.2%, 71.9% and 71.9%, respectively. There was a statistical difference between VC and SSD. MPR could determine accurately the circumference of colorectal carcinoma, Raysum could determine the length of lesion more precisely than SSD, VC was helpful in discriminating pathology patterns.

CONCLUSION: MPR, VC, SSD and Raysum have advantage and disadvantage in detection of colorectal carcinoma, use of these methods in combination can disclose the lesion more accurately.

Characterization of lesions missed on interpretation of CT colonography using a 2D search method

OBJECTIVE

We examined potential factors that may cause false-negative results on CT colonography examinations.

MATERIALS AND METHODS

In this prospective and retrospective study, 500 asymptomatic patients at high risk for colorectal cancer underwent CT colonography and colonoscopy. Each CT data set was interpreted by two independent observers, who were unaware of endoscopic findings, using a method of searching through enlarged axial images to detect intraluminal lesions. Another observer identified and characterized lesions missed at prospective interpretation. Polyps were assessed for size, method of visualization, intrinsic and extrinsic features, and examination quality.

RESULTS

We found 116 polyps at least 5 mm in diameter, 54 (47%) of which were missed by at least one of the prospective observers. Polyps seen in only one position were missed more often than polyps seen in both supine and prone positions (84% vs 50%, p < 0.01). Polyps located in suboptimally prepared colonic segments or along a thickened colonic wall were more frequently missed (p = 0.02 and p = 0.05, respectively). Endoscopic morphology and irregular surface contour were associated with missed lesions of all sizes (p = 0.03 and p = 0.04, respectively). Rounded intraluminal lesions were detected more often than other morphologies on CT (p = 0.04).

CONCLUSION

Factors that influence the likelihood that a polyp may be missed at interpretation of CT colonography include being seen only in one position, having flat endoscopic or CT morphology, having surface irregularity, and being located in a poorly prepared segment or along a thickened colonic wall. Understanding these features should lead to improved polyp detection on CT colonography.

Sensitivity and specificity of pneumo-colon CT in detecting colorectal neoplasms

AIM: To evaluate the sensitivity and specificity of pneumocolon computed tomography (CT) in the detection of colorectal neoplasms.

METHODS: A total of 100 patients with suspected colorectal neoplasms underwent both pneumocolon CT and colonoscopy.

RESULTS: On colonoscopy 13 colorectal carcinomas were detected in 13 patients, and 46 polyps in 24 patients (11 polyps were ≥ 1 cm in diameter, 14 were 6-9 mm, and 21 were ≤ 5 mm). Pneumocolon CT detected 15 cancers (included one false positive cancer), but only 16 polyps (9 were ≥ 1 cm). This resulted in a sensitivity of 100% (95% confidence interval (CI) 75%-100%) and specificity of 93% (95%CI: 66%-100%) for detection of colorectal carcinoma, and a sensitivity of 93% (95%CI: 73%-99%) and specificity of 96% (95%CI: 78%-100%) for detection of carcinoma and/or ≥ 1 cm polyps. Pneumocolon CT also identified carcinoma not seen at colonoscopy in one patient, and detected metastases in 2 colorectal carcinoma patients and extracolonic carcinoma in one patient.

CONCLUSION: Pneumocolon CT has a high sensitivity and specificity for detection of colorectal carcinoma and/or ≥1 cm colorectal polyps but not for < 1 cm colorectal polyps. Pneumocolon CT may be suitable for initial investigation of patients with symptoms of colorectal malignancy.

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 of Colorectal Polyps:A Metaanalysis

OBJECTIVE

For proper evaluation of the accuracy of CT colonography, prospective multiinstitutional trials would be ideal. Until these trials are available, data can be collectively analyzed. The purpose of this study is to use metaanalysis to assess the reported accuracy of CT colonography compared with conventional colonoscopy for detecting colorectal polyps.

MATERIALS AND METHODS

Articles comparing CT colonography and conventional colonoscopy were identified, and a standardized form was used to extract relevant study data. Fisher's exact test and the Mantel-Haenszel test were used for pooling of data. A 95% confidence interval (CI) was selected to determine sensitivity and specificity, and the Kruskal-Wallis exact test was used to identify trends relating to polyp size. Meta-analysis methods were used to test strength of results. Comparisons were made for the percentage of polyps detected grouped by size (> or = 10 mm, 6-9 mm, < or = 5 mm) and the percentage of patients identified who had polyps of the same size.

RESULTS

Fourteen studies fulfilled all the study inclusion criteria and gave a total of 1,324 patients and 1,411 polyps. The pooled per-patient sensitivity for polyps 10 mm or larger was (sensitivity [95% CI]) 0.88 (0.84-0.93), for polyps 6-9 mm it was 0.84 (0.80-0.89), and for polyps 5 mm or smaller it was 0.65 (0.57-0.73). The pooled per-polyp sensitivity for polyps 10 mm or larger was 0.81 (0.76-0.85), for polyps 6-9 mm it was 0.62 (0.58-0.67), and for polyps 5 mm or smaller it was 0.43 (0.39-0.47). Sensitivity for detection of polyps increased as the polyp size increased (p < 0.00005). The pooled overall specificity for detection of polyps larger than 10 mm was 0.95 (0.94-0.97).

CONCLUSION

The specificity and sensitivity of CT colonography are high for polyps larger than 10 mm.

Virtual colonoscopy compared with conventional colonoscopy for stricturing postoperative recurrence in Crohn's disease

BACKGROUND

The place of virtual colonoscopy (VC) in patients with Crohn's disease (CD) requiring endoscopic follow-up after surgery is unknown. The authors compared findings from VC versus conventional colonoscopy (CC) for assessing the postoperative recurrence of CD.

METHODS

Sixteen patients with ileocolonic anastomosis for CD were prospectively enrolled from January 2001 to January 2002. Recurrence was assessed by CC according to Rutgeerts et al. VC was performed with a computed tomography scanner, with images examined by three radiologists who were unaware of the endoscopic findings.

RESULTS

CC showed perianastomotic recurrence in 15 of 16 patients. Perianastomotic narrowing or stenosis was detected by VC in 11 of these 15 patients. There were 11 true positive, 1 true negative, 0 false-positive, and 4 false-negative findings (73% sensitivity, 100% specificity, 100% positive predictive value, 20% negative predictive value, 75% accuracy). Among the eight patients showing a rigid stenosis of the anastomosis not allowing passage of the colonoscope, VC detected narrowing or stenosis in seven patients.

CONCLUSIONS

The current findings suggest that although the widespread use of VC in CD is currently not indicated because of possible false-negative findings, this technique may represent an alternative to CC in noncompliant postsurgical patients with a rigid stenosis not allowing passage of the endoscope.

Three-dimensional display modes for CT colonography: conventional 3D virtual colonoscopy versus unfolded cube projection

The authors compared a conventional two-directional three-dimensional (3D) display for computed tomography (CT) colonography with an alternative method they developed on the basis of time efficiency and surface visibility. With the conventional technique, 3D ante- and retrograde cine loops were obtained (hereafter, conventional 3D). With the alternative method, six projections were obtained at 90 degrees viewing angles (unfolded cube display). Mean evaluation time per patient with the conventional 3D display was significantly longer than that with the unfolded cube display. With the conventional 3D method, 93.8% of the colon surface came into view; with the unfolded cube method, 99.5% of the colon surface came into view. Sensitivity and specificity were not significantly different between the two methods. Agreements between observers were kappa = 0.605 for conventional 3D display and kappa = 0.692 for unfolded cube display. Consequently, the latter method enhances the 3D endoluminal display with improved time efficiency and higher surface visibility.

CT colonography: Protocol optimization with multi-detector row CT--study in an anthropomorphic colon phantom

PURPOSE

To determine optimal detector collimation, section thickness, and tube current for multi-detector row computed tomography (CT) colonography.

MATERIALS AND METHODS

An anthropomorphic colon phantom with simulated polyps of varying size (2, 6, 8, 10, and 12 mm) was examined by using multi-detector row CT with varying combinations of detector collimation (4 x 1.0 mm and 4 x 2.5 mm), dose per section (10, 20, 40, 60, 80, 100, and 140 mAs), and section thickness/reconstruction interval (1.25/0.6, 2.0/1.0, 3.0/1.0, and 5.0/2.0 mm). Polyp depiction, longitudinal polyp distortion, and presence of rippling artifacts were assessed on reformatted three-dimensional endoluminal images by three reviewers.

RESULTS

Longitudinal distortion and rippling artifacts increased with increasing section thickness and use of broader detector collimation. Polyps 8 mm or larger were depicted with any combination of section thickness, detector collimation, and tube current. Depiction of polyps 6 mm or smaller depended on the detector collimation/reconstructed section thickness and was rated optimal for the 4 x 1.0-mm detector collimation with a section thickness of 1.25 mm. This was also observed for low-dose protocols. Polyps 6 mm or smaller that were not detected with 3-mm section thickness and 4 x 2.5-mm detector collimation were detected with 1.25-mm section thickness and 10 mAs.

CONCLUSION

A narrow detector collimation with thin-section imaging (4 x 1.0-mm detector collimation, 1.25-mm section thickness) is a prerequisite for low-dose (10-mAs) multi-detector row CT colonography.

Multislice CT colonography: current status and limitations

CT colonography (CTC) is a promising method for colorectal screening providing a full structural evaluation of the entire colon and gaining in popularity due to a superior safety profile, a low rate of complications, and high patient acceptance. Multislice CT (MSCT) has further improved the diagnostic potential of CTC by generating high-resolution CT images of the abdomen and pelvis in shorter acquisition times than was previously possible. Over the past year, multiple studies have been published on every aspect of CTC including techniques, image display, image reconstruction, and clinical trial results assessing the feasibility of CTC as a screening tool. Yet despite increasing clinical use, the appropriate role of CTC in colorectal cancer screening remains undefined and barriers to widespread adoption remain. In particular, though the test is generally regarded as easy to perform, accurate interpretation requires a steep learning curve. While several large studies have found high sensitivity and specificity, the accuracy of CTC in a screening population has yet to be verified and almost no health insurance plans reimburse for its use in colorectal screening. Ongoing research in computer-aided detection and new software tools, however, have the potential to increase accuracy and ease of interpretation significantly, accelerating its acceptance as a colorectal screening tool.

Colorectal neoplasms: role of intravenous contrast-enhanced CT colonography

PURPOSE

To evaluate whether computed tomographic (CT) colonography with intravenously administered contrast material can help predict malignant differentiation of colorectal neoplasms (> or =10 mm in diameter).

MATERIALS AND METHODS

Enhancement of 29 consecutive colorectal neoplasms on pre- and postcontrast CT colonographic images was retrospectively measured. The neoplasms were subsequently resected. Enhancement was calculated by subtraction of attenuation values (in Hounsfield units) obtained with precontrast and postcontrast 45-second-delay prone CT colonographic sequences. The neoplasms were graded as follows: grade 1, adenoma; grade 2, adenoma with high-grade dysplasia; grade 3, well-differentiated adenocarcinoma; grade 4, moderately differentiated adenocarcinoma; and grade 5, poorly differentiated adenocarcinoma. Correlation among size, histologic grade, and degree of enhancement was made with Pearson and Spearman coefficients. The ability of the degree of enhancement to help predict adenocarcinoma (histologic grade, > or =3) was calculated.

RESULTS

Histologic-CT colonographic correlation was performed in 29 neoplasms (mean diameter, 27.9 mm; range, 10-65 mm). There was no correlation between size and degree of enhancement, size and histologic grade (R = -0.17, P =.33), or histologic grade and degree of enhancement (R = 0.23, P =.23). However, increasing enhancement was noted between grades 2 and 5. When an enhancement threshold of 40 HU was used for the diagnosis of adenocarcinoma (grades 3-5), sensitivity was 92%, specificity was 20%, positive predictive value was 50%, and negative predictive value was 75%.

CONCLUSION

The degree of contrast enhancement on a 45-second-delay CT colonographic image does not correlate with size or degree of histologic differentiation, although increasing enhancement with lesser degrees of differentiation was noted.

Colorectal cancer screening: scientific review

CONTEXT

Screening for colorectal cancer clearly reduces colorectal cancer mortality, yet many eligible adults remain unscreened. Several screening tests are available, and various professional organizations have differing recommendations on which screening test to use. Clinicians are challenged to ensure that eligible patients undergo colorectal cancer screening and to guide patients in choosing what tests to receive.

OBJECTIVE

To critically assess the evidence for use of the available colorectal cancer screening tests, including fecal occult blood tests, sigmoidoscopy, colonoscopy, double-contrast barium enema, and newer tests, such as virtual colonoscopy and stool-based molecular screening.

DATA SOURCES

All relevant English-language articles were identified using PubMed (January 1966-August 2002), published meta-analyses, reference lists of key articles, and expert consultation.

DATA EXTRACTION

Studies that evaluated colorectal cancer screening in healthy individuals and assessed clinical outcomes were included. Evidence from randomized controlled trials was considered to be of highest quality, followed by observational evidence. Diagnostic accuracy studies were evaluated when randomized controlled trials and observational studies were not available or did not provide adequate evidence. Studies were excluded if they did not evaluate colorectal screening tests and if they did not evaluate average-risk individuals.

DATA SYNTHESIS

Randomized controlled trials have shown that fecal occult blood testing can reduce colorectal cancer incidence and mortality. Case-control studies have shown that sigmoidoscopy is associated with a reduction in mortality, and observational studies suggest colonoscopy is effective as well. Combining fecal occult blood testing and sigmoidoscopy may decrease mortality and can increase diagnostic yield.

CONCLUSION

The recommendation that all men and women aged 50 years or older undergo screening for colorectal cancer is supported by a large body of direct and indirect evidence. At present, the available evidence does not currently support choosing one test over another.

Stool tagging applied in thin-slice multidetector computed tomography colonography

OBJECTIVE

To compare thin-slice multidetector computed tomography colonography (CTC) that uses stool tagging with colonoscopy.

METHOD

One hundred fifty patients scheduled for colonoscopy underwent high-resolution CTC. An iodinated contrast agent was added to the preparation to tag the residual colonic fluid and stool. The effect of fluid tagging was assessed first. Sensitivity and specificity were calculated for two independent readers. In addition, values were recalculated separately for the first and last 75 patients.

RESULTS

Tagging was optimal in 95.3% of the cases, and reader confidence was high. Sensitivities were 64.1%-66.7% (for the 2 readers) for 5- to 9-mm polyps and 91.7% for larger polyps. The overall specificity was 94.2% and 95%. Sensitivity improved during the study for both 5- to 9-mm polyps (from 54.2%-58.3% to 80%) and polyps larger than 9 mm (from 50% to 100%). Specificity changed nonuniformly.

CONCLUSION

The combination of fluid tagging and high-resolution scanning in CTC showed high sensitivity and specificity, especially concerning sensitivity for polyps of 10 mm and larger.

Virtual colonoscopy: past, present, and future

Virtual colonoscopy is developing into a practical clinical technique. The issues of the steep learning curve and accuracy of the technique are undergoing advances related to patient preparation, scanning technique, reading methods, and CAD. It is probably the best test for patients with an incomplete colonoscopy or for those patients who cannot undergo colonoscopy. Its precise role in screening average-risk patients for colon cancer remains to be defined by ongoing research and clinical trials.

Unusual causes of colonic wall thickening on computed tomography

Computed tomography (CT) appearances in "colitis" are often non-specific, and include mural thickening and mesenteric fat stranding. In the western world, the majority of cases will have, or be subsequently diagnosed with, inflammatory bowel disease, pseudomembranous colitis or ischaemic colitis. However, other rare conditions may also produce these rather non-specific signs. We present a number of cases demonstrating colonic wall thickening on CT due to rarer diagnoses, which are correlated with the histopathological features. Some of these CT appearances have not been described previously in the literature.

Virtual endoscopy: current perspectives

Virtual endoscopy is a new method for evaluating the gastrointestinal tract using either thin-section computed tomography (CT) or magnetic resonance imaging (MRI). The acquired data are then subjected to computer manipulation to render images simulating the conventional endoscopic view. CT and MR imaging data can provide information that is not accessible endoscopically. These important features include information on tissue extending through and beyond organ walls and the anatomic context of the entire gastrointestinal tract, which permits correct anatomic localization of the lesion. Many clinical studies have shown that it is a safe, noninvasive, well-tolerated alternative to conventional endoscopy. Virtual endoscopy may have potential as a method of screening for colorectal cancer. This review describes the technique, reviews reported results, and discusses the present and future applications of this technique, focusing on CT colography (CTC).

CT colonography (virtual colonoscopy) for the detection of colorectal polyps and neoplasms. current status and future developments

Computed tomography colonography (CTC) is a new, rapidly developing non-invasive CT technique used to detect colonic polyps and cancers. It employs two- (2D) and three-dimensional (3D) images of the colon in order to display neoplastic lesions. Clinical trials demonstrate promising results for the detection of polyps and cancers greater than or equal to 10 mm in size. Our purpose is to describe the technique of CT colonography, review recent published trials of CT colonography, and elucidate current clinical applications. Continuing technical innovations such as multidetector CT, computer-aided diagnosis, new image display techniques and faecal tagging promise to improve the performance and patient acceptance of CT colonography in the future.

CT colonography: multiobserver diagnostic performance

PURPOSE

To prospectively evaluate multiobserver diagnostic performance and reader agreement for colorectal polyp detection in a well-characterized cohort of patients with increased number of polyps, compared with an average-risk patient, with colonoscopy as the reference standard.

MATERIALS AND METHODS

A cohort of 70 patients suspected of having polyps was examined with spiral computed tomographic (CT) colonography, with colonoscopy performed the same day. After air insufflation per rectum, supine and prone images were obtained with single-detector row CT (5-mm collimation, 8-mm table increment, 2-mm reconstruction interval). Images were analyzed independently by four experienced abdominal radiologists using two-dimensional multiplanar reformation followed by selective use of three-dimensional endoscopic volume-rendered images. Data were analyzed both per polyp and per patient.

RESULTS

Analysis per polyp demonstrated a pooled sensitivity of 0.68 for lesions 10 mm or larger (n = 40), with 75% agreement among the four readers. Analysis per patient demonstrated improved detection and agreement, with a pooled sensitivity of 0.88 for patients with polyps or cancers 10 mm or larger (n = 28), with 94% agreement. When sensitivity and receiver operating characteristic analyses were analyzed per polyp size threshold, results among readers converged and peaked at polyp diameters of approximately 10 mm.

CONCLUSION

In this patient cohort, diagnostic performance and interobserver agreement with single-detector row CT colonography was sufficient for detection of patients with lesions 10 mm or larger, with more variable results for smaller polyps.

Colon cancer screening strategies

Screening has been shown to reduce morbidity and mortality related to colorectal cancer. However, the optimal strategy for population screening for colorectal cancer has been a topic of heated debate. Recent studies have challenged the efficacy and cost-effectiveness of current population screening practices. Novel approaches to improve the assessment of an individual's colorectal cancer risk and advances in technology are changing our approach to colorectal screening. This review covers current guidelines for screening for colorectal cancer, recent advances in cancer risk assessment, and the role of endoscopy, virtual colonoscopy, and fecal DNA testing in colorectal cancer screening.

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.

Dietary fecal tagging as a cleansing method before CT colonography: initial results polyp detection and patient acceptance

PURPOSE

To compare reduced colonic cleansing based on dietary fecal tagging (FT) with standard (non-FT) colonic cleansing with regard to patient acceptance, sensitivity, and specificity.

MATERIALS AND METHODS

In 50 patients (FT group), FT was performed by means of diet, magnesium citrate, and a barium suspension. In another 50 patients (non-FT group), preparation was based on polyethylene glycol administration. All patients underwent conventional colonoscopy after computed tomographic (CT) colonography. Sensitivity and specificity for polyp detection were calculated by using conventional colonography as the reference standard. At CT colonography, fecal residue was evaluated. Patients were interviewed to determine discomfort, side effects, sleep quality, final opinion on examination comfort, and whether they would be reluctant to undergo the same examination again.

RESULTS

FT left more fecal residue but improved differentiation from polyps (FT specificity, 88% [30 of 34 patients]; non-FT, 77% [23 of 30 patients]). Sensitivities were comparable: FT, 88% (14 of 16 patients); non-FT, 85% (17 of 20 patients). FT significantly reduced discomfort, side effects, and sleep disturbance, and resulted in an improved final opinion of how comfortable the examination was (P <.05). Although FT improved patient willingness to repeat the examination, this improvement was not statistically significant (P >.05).

CONCLUSION

FT offers the patient a well-tolerated preparation and improves specificity, with improved differentiation of polyps from residual stool.

CT colonography at different radiation dose levels: feasibility of dose reduction

PURPOSE

To investigate the sensitivity and specificity of polyp detection and the image quality of computed tomographic (CT) colonography at different radiation dose levels and to study effective doses reported in literature on CT colonography.

MATERIALS AND METHODS

CT colonography and colonoscopy were performed with 100 mAs in 50 consecutive patients at high risk for colorectal cancer; 50- and 30-mAs CT colonographic examinations were simulated with controlled addition of noise to raw transmission measurements. One radiologist randomly evaluated all original and simulated images for the presence of polyps and scored image quality. Differences in image quality were assessed with the Wilcoxon rank test. Scan protocols from the literature and recent (unpublished) updates were collected.

RESULTS

In nine of 10 patients with polyps 5 mm in diameter or larger (sensitivity, 90%) and in seven of 17 patients with polyps smaller than 5 mm, polyps were correctly identified with CT colonography at all dose levels. Specificity for patients without polyps 5 mm or larger was 53%-60% at all dose levels and for patients without any polyps was 26% (at 100 and 50 mAs) and 48% (at 30 mAs). Image quality decreased significantly as the dose level decreased. The median effective doses (supine and prone positions) calculated from protocols reported in the literature and updates were 7.8 and 8.8 mSv, respectively.

CONCLUSION

Although image quality decreases significantly at 30 mAs (3.6 mSv), polyp detection remains unimpaired. The median dose for CT colonography at institutions that perform CT colonographic research is currently 8.8 mSv.

Colon cancer: detection and prevention

Recent data have advanced our ability to detect, survey, and manage patients with colonic neoplasia. Current studies and consensus statements increasingly support the role of colonoscopic screening over less invasive testing such as FOBT or FS for appropriately selected individuals. There are many issues, however, that remain unresolved. What is the appropriate surveillance of an individual with a single family member who had colon cancer at an early age? How should family members of suspected HNPCC kindreds be managed? There has yet to be a prospective cohort validation of the Bethesda criteria in directing clinical practice, with the endpoint of mortality reduction. Questions regarding prophylaxis with dietary supplements and medications are exciting areas that are currently under study. As newer technologies become clinically available for molecular diagnostics and screening, and virtual colonoscopy with computed tomography and magnetic resonance disseminates, there will undoubtedly be new questions to be answered regarding their ability to aid in the detection and management of colon cancer.

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.

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.

Computed tomography colonography

Computed tomography colonography (virtual colonoscopy) is an exciting technique that continues to evolve but promises to be a valuable tool for diagnosis of and screening for colorectal neoplasia.

Virtual colonoscopy: the endoscopist's point of view

The major advantage of virtual colonoscopy is that it might increase acceptance of colorectal cancer (CRC) screening. Its disadvantages are high costs and unknown sensitivity and specificity if widely applied. It might replace colonoscopy to a substantial degree only if no bowel preparation is necessary. Gastroenterologists have to include virtual colonoscopy as a complementary method to colonoscopy. Virtual colonoscopy may increase the ratio of therapeutic colonoscopies compared with simple "diagnostic" procedures.