The diagnostic value of computed tomography (CT) of the liver depends on proper conduct of the examination, knowledgeable interpretation of findings, and an appreciation of the capabilities and limitations of the method. This report documents 10 months of experience with abdominal CT in more than 600 liver examinations using a system fast enough to eliminate respiratory motion. This experience supplied data on the CT appearance of the normal liver and its variations and of various hepatic abnormalities, on the conduct of the examination, including the appropriate of contrast material, and on some of the problems that reduce the technical quality of the examination. CT was highly accurate, but not infallible, in detecting and defining space-occupying lesions and in detecting fatty infiltration; it was less helpful in detecting diffuse hepatic disease. In bile duct obstruction, CT displayed not only the dilated ducts but often the obstructing lesion.

2Department of Radiology, Mayo Clinic Rochester, Mayo East 2-B, 200 First St. SW, Rochester, MN 55905. Address correspondence to J. G. Fletcher. T colonography, or virtual colonoscopy, is now routinely used as a full structural examination of the colorectum following incomplete endoscopy [1] and in patients with elevated risk for complications during endoscopy or with aversion to endoscopy. CT colonography has demonstrated performance on par with optical colonoscopy in the screening of asymptomatic patients for adenomatous polyps in some hands [2] and has performed superiorly compared with nonendoscopic alternatives [3]. Optimal colonic inflation is essential to a high-quality CT colonography examination. Given the speed of image acquisition and reconstruction of MDCT scanners, patients must tolerate maximum inflation for only a few seconds, as opposed to endoscopy and barium enema, in which the colon remains inflated for much longer periods of time. Nevertheless, colonic insufflation is known to result in perforation, ranging from approximately 0.004–0.01% of cases for double contrast barium enema [4, 5] to 0.07–0.19% of cases for colonoscopy [6, 7]. To date, thousands of patients have undergone CT colonography without complications. Two cases of colonic perforation at CT have recently been reported in patients with known colonic disease [8, 9]. We report a case of perforation following CT colonography in a patient without known colonic disease.

OBJECTIVE:Our purpose was to determine the prevalence of polyps that are invisible on CT colonography (CTC) in a population previously screened for colorectal neoplasms. Differences in the prevalence of occult polyps in various populations might help explain the discordant reported sensitivities for polyp detection in published reports of CTC.SUBJECTS AND METHODS:Seventy-five consecutive patients who had been previously screened for polyps underwent same-day colonoscopy and CTC. Many of the patients had personal histories of previous polypectomies and were undergoing surveillance colonoscopy. The scans were interpreted prospectively by an experienced radiologist. Polyps missed prospectively on CTC were analyzed retrospectively by three experienced radiologists and categorized as perception errors (visible in retrospect), technical errors (e.g., obscured by feces or fluid), or occult (invisible).RESULTS:Thirty polyps 5 mm or larger were found at colonoscopy, 18 of which were missed prospectively on CTC. Of the 18 missed polyps, 12 could not be identified in retrospect, even though they were located in clean, dry, well-distended colonic segments. These were classified as occult. Ten of the 12 occult polyps showed flat morphology on review of colonoscopy video recordings. Of the remaining six missed polyps, two were classified as perception errors, two as technical errors, and two as a combination of technical and perception error.CONCLUSION:In this population, colonographically occult polyps were common and accounted for more detection failures than perception errors and technical errors combined. The high prevalence of occult polyps may be explained by the fact that previous screening may have led to removal of easy-to-see polyps, creating a study population with a higher percentage of hard-to-see polyps.

OBJECTIVE Using a 3D rendering technique called "virtual dissection," we sought to evaluate polyp and fold distortion using a colon phantom, estimate the polyp detection performance in humans, and estimate the added benefit of double interpretation and computer-aided diagnosis. MATERIALS AND METHODS A colon phantom containing 144 polyps of varying sizes (5-12 mm) and shapes (flat, sessile, pedunculated) was scanned. Polyp shape and distortion at virtual dissection were categorized as flame, club, pea, or bizarre. Haustral fold distortion was graded. The CT colonography examinations in 20 consecutive patients (colonoscopically proven normal findings, n = 5; polyps > or = 1 cm, n = 17 in 15 patients) were blindly reviewed by three radiologists using the virtual dissection technique. The added benefits of double interpretation and computer-aided diagnosis were tabulated. RESULTS Sessile polyps appeared flame (35/48 [73%]) or pea (11/48 [23%]) in shape. Flat polyps appeared flame-shaped (31/47 [66%]) or pea-shaped (16/47 [34%]). Pedunculated polyps were flame (15/45 [33%]), club (20/45 [44%]), or pea (6/45 [13%]) in shape. Axial distortion occurred along the longitudinal axis. The sensitivities of the three observers for polyps of 1 cm or more were 16/17 (94%), 14/17 (82%), and 15/17 (88%). The specificities were 5/5 (100%), 5/5 (100%), and 4/5 (80%). Sensitivities after double interpretation and computer-aided diagnosis improved but did not reach statistical significance. CONCLUSION Although distortion of colonic structures exists at virtual dissection, it does so in recognizable patterns, so that sensitivity for polyp detection is not compromised.

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.

Background & Aims: To assess the prevalence and spectrum of extracolonic findings in a screening population undergoing computed tomography colonography (CTC), and to evaluate the short-term direct medical costs incurred from subsequent radiologic follow-up evaluation. Methods: Six hundred and eighty-one asymptomatic patients undergoing colonoscopy screening consented to a CTC examination. Extracolonic CT findings were classified into high, medium, and low importance. Clinical and radiologic follow-up, missed lesions, and outcomes were assessed by chart review (time interval, 410-1513 days; median, 913 days). Short-term direct medical costs of radiologic follow-up were determined based on Medicare 2002 reimbursement rates. Results: Extracolonic findings were found commonly. These were categorized as high clinical importance in 71 (10%) individuals, as medium importance in 183 individuals (27%), and as low importance in 341 individuals (50%). Subsequent medical or surgical interventions resulted from these findings in 9 of the 681 patients (1.3%). Costs of subsequent radiologic follow-up studies were calculated as $23,380.59 (average added costs per CTC examination $34.33). Conclusions: CTC commonly detects extracolonic findings that can be considered clinically important when applied to an asymptomatic screening population. Although such incidental findings add benefit to the screening intervention, moderate incremental costs are incurred based on additional radiologic procedures generated during short-term follow-up.

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 greater than or equal to1 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 greater than or equal to1 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 K 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.

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 ≥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 ≥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 ≥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.

BACKGROUND & AIMS The influence of preoperative staging of rectal carcinoma on therapeutic decisions is uncertain. The use of fine-needle aspiration (FNA) of perirectal nodes in this setting has not been evaluated. The aim of this prospective, blinded study of patients with rectal cancer was to assess the impact of preoperative staging on treatment decisions and compare the tumor (T), nodal (N) staging performance characteristics of pelvic computed tomography (CT), rectal endoscopic ultrasonography (EUS), and EUS FNA. METHODS Eighty consecutive patients with newly diagnosed rectal cancer were prospectively evaluated. Therapy decisions were recorded after sequential disclosure of staging information to the patient's surgeon. RESULTS In 31% of patients (95% confidence interval, 21%-42%), EUS staging information changed the surgeon's original treatment plan based on CT alone. The further addition of FNA changed therapy in one patient. T staging accuracy was 71% (CT) and 91% (EUS) (P = 0.02); N staging accuracy was 76% (CT), 82% (EUS), and 76% (EUS FNA) (P = NS). CONCLUSIONS Preoperative staging with EUS results in more frequent use of preoperative neoadjuvant therapy than if staging was performed with CT alone. The addition of FNA only changed the management of one patient, whereas FNA did not significantly improve N staging accuracy over EUS alone. FNA seems to offer the most potential for impacting management in those patients with early T stage disease, and its use should be confined to this subgroup of patients. EUS is more accurate than CT for determining T stage of rectal carcinoma.

BACKGROUND:We investigated whether flat lesions of the colon could be detected on computed tomographic colonography (CTC).METHODS:CTC and conventional colonoscopy were performed on 547 consecutive patients. A subset of 22 polyps was described as flat on colonoscopy (n = 16) or CTC (n = 6) and are the basis of this report. CTC was performed with a standard technique (5-mm collimation, 3-mm reconstruction intervals). Patients were scanned in supine and prone positions. Examinations were randomly assigned and reviewed in a blinded fashion by two of three radiologists. Prospective interpretations were recorded. All patients had conventional colonoscopy, which served as the gold standard.RESULTS:Twenty-two flat lesions ranging from 0.4 to 3.5 cm were histologically classified as adenomatous (n = 8) or hyperplastic (n = 14). The sensitivities for detecting all flat lesions and flat adenomas by each reviewer were 43% and 100%, 65% and 100%, and 15% and 13%, respectively. "Double reading" resulted in detection of 68% of all lesions and 100% of adenomas. Of the seven hyperplastic polyps missed by both reviewers, four were identified retrospectively.CONCLUSION:Flat lesions of the colon represent an important source of false negative CTC examinations. Awareness of their morphology can assist radiologists in finding most of these challenging lesions.

PURPOSE To compare respiratory artifacts, colonic distention, and polyp detection at computed tomographic (CT) colonography by using single- and multi-detector row helical CT systems. MATERIALS AND METHODS A total of 237 consecutive patients received subcutaneously administered glucagon and underwent prone and supine CT colonography with single-detector row CT (n = 77) and multi-detector row CT (n = 160), followed by colonoscopy. Examination results were graded for colonic distention, respiratory artifacts, and polyp depiction by two radiologists working independently. RESULTS Suboptimal colonic distention was significantly more common with single-detector row CT and was present in at least one segment in 52% (40 of 77 patients) of examinations versus only 19% (30 of 160 patients) with multi-detector row CT (P <.001). Mild respiratory artifacts were present in 61% (47 of 77 patients) of single-detector row CT examinations versus only 16% (26 of 160 patients) of multi-detector row CT examinations (P <.001). Depiction of polyps larger than 10 mm was 89% (eight of nine polyps) for single-detector row CT and 80% (eight of 10 polyps) for multi-detector row CT (P >.05). CONCLUSION CT colonography performed with multi-detector row CT significantly improved the demonstration of colonic distention and depicted fewer respiratory artifacts compared with single-detector row CT. No significant differences in the depiction of polyps larger than 10 mm were demonstrated between single- and multi-detector row CT for a small number of polyps. Studies with a larger prevalence of clinically important polyps are needed for further evaluation of differences in polyp detection.

We describe an unusual presentation of Enterobius vermicularis infestation. Computed tomography showed wall thickening in the distal ileum and cecum, with fat stranding, ascites and mesenteric adenopathy. Fluoroscopic examination confirmed distal ileal transverse fold thickening. Isolation of Enterobius vermicularis in stool and biopsy confirmed the diagnosis. Enterobius should be included among the causes of eosinophilic ileocolitis.

PURPOSETo assess the added benefits of prone positioning in addition to supine positioning and oral iodinated contrast medium for help in the detection of colonic polyps at computed tomographic (CT) colonography.MATERIALS AND METHODSCT colonography was performed in prone and supine positions in 180 patients with polyps or risk factors for colonic neoplasia. Patients were randomly assigned to receive a standard bowel preparation or a standard preparation plus oral iodinated contrast medium. One radiologist interpreted supine images alone, and another analyzed supine and prone images. All patients subsequently underwent colonoscopy.RESULTSAt colonoscopy, 121 large (> or =1-cm-diameter) polyps and 142 smaller (0.5-0.9-cm) polyps were identified. Prone positioning resulted in increased sensitivity for identification of patients with large (> or =1-cm) polyps (increase from 70% to 85%, P: =.004) and of patients with polyps 0.5 cm or larger (increase from 75% to 88%, P: <.005), with no change in specificity. Use of oral contrast medium did not significantly improve polyp detection even in the subset of patients in whom colonic fluid attenuation was markedly increased.CONCLUSIONAcquisition and review of supine and prone CT colonographic images significantly improves the ability to identify patients with polyps 0.5 cm in diameter or larger. Administration of oral iodinated contrast medium does not significantly improve polyp detection.

Background: The purpose of the study was to describe the computed tomographic (CT) findings of the alimentary canal and mesentery in amyloid infiltration of the gastrointestinal (GI) tract and to correlate the CT findings with histologic extent and distribution and with amyloid subtype.Methods: Abdominal CT scans performed between 1988 and 1997 on patients with pathologically proven amyloidosis of the alimentary canal were reviewed for abnormalities of the alimentary canal and mesentery. Histology was graded for extent of mucosal, submucosal, and muscularis propria involvement and for degree of interstitial and vascular distribution. CT findings were correlated with histologic extent, histologic distribution, and amyloid histochemical type.Results: Twenty-three patients were included. Four (17%) had bowel wall thickening, which was associated with a higher submucosal extent and interstitial distribution than in patients with normal bowel by CT. Four (17%) patients had bowel wall dilatation without thickening, which was not associated with statistically significantly different histology than in patients with normal bowel by CT. There was no statistically significant correlation between CT findings and histochemical subtype. Mesenteric soft tissue infiltration was seen in two patients, and mesenteric adenopathy was seen in one patient.Conclusions: Normal bowel is a common abdominal CT finding in amyloidosis of the alimentary canal. When findings are present, GI wall thickening and/or bowel wall dilatation without wall thickening may be seen. Bowel wall thickening on CT correlates with submucosal extent and interstitial distribution of disease. Soft tissue infiltration and adenopathy are also occasionally seen.