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Original Research |
1 Department of Radiology, University of Wisconsin Medical School, E3/311
Clinical Science Center, 600 Highland Ave., Madison, WI 53792-3252.
2 Section of Gastroenterology and Hepatology, University of Wisconsin Medical
School, Madison, WI.
Received February 13, 2007;
revised May 20, 2007;
P. J. Pickhardt is on the clinical advisory board of Viatronix, Inc.
Abstract
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MATERIALS AND METHODS. The clinical data and CTC examinations were reviewed in 100 patients who underwent CTC after incomplete optical colonoscopy. The findings were compared with a control group of 100 patients who underwent complete optical colonoscopy after CTC. The interactive 3D colon map and 2D multiplanar reconstruction images from CTC were reviewed independently by two experienced gastrointestinal radiologists for colorectal length (total, sigmoid colon, and transverse colon), number of acute angle flexures (reflecting tortuosity), and advanced diverticular disease. Discrepancies were resolved by secondary consensus review.
RESULTS. Significant differences existed between the complete and incomplete optical colonoscopy groups, respectively, for age (mean, 58.2 vs 63.4 years; p < 0.001), sex (60 men and 40 women vs 41 men and 59 women; p < 0.01), and prior abdominal surgery (26.0% vs 48.0%; p < 0.01). Significant differences were seen between the complete and incomplete optical colonoscopy groups, respectively, for all the CTC factors that were evaluated: total colorectal length (mean, 167.0 vs 210.8 cm; p < 0.0001), sigmoid colon length (mean, 48.7 vs 66.8 cm; p < 0.0001), transverse colon length (mean, 49.2 vs 66.3 cm; p < 0.0001), number of flexures (mean, 9.6 vs 11.9; p < 0.0001), and advanced diverticular disease (22.0% vs 34.0%; p <0.05).
CONCLUSION. Anatomic features associated with failure to reach the cecum at optical colonoscopy included colonic elongation, tortuosity, and advanced diverticular disease. These predictive factors may have implications for optical colonoscopy training and performance and for patients sent to optical colonoscopy for polyps prospectively detected at CTC.
Keywords: anatomy • colorectal cancer • colonoscopy • CT colonography • oncologic imaging • screening colonoscopy
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Patient factors that most significantly correlate with incomplete optical colonoscopy are female sex, increasing patient age, diverticular disease, and history of abdominal surgery. Additional patient factors that have been reported include low body mass index (BMI), history of constipation, laxative use, and prior incomplete optical colonoscopy.
Endoscopist factors that may influence optical colonoscopy completion include prior experience, the specific techniques used, and the particular equipment used. Although the barium enema has been used previously to estimate colon length, CT colonography (CTC) is a more precise tool for assessing the anatomy and length of this complex 3D structure. The goal of this study was to compare both clinical and CTC findings in patients who underwent complete versus incomplete optical colonoscopy.
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Optical colonoscopy reports were reviewed for each patient in the incomplete study group to determine the segmental level reached at optical colonoscopy and the reasons cited by the endoscopist for the incomplete examination. The most common proximal segments reached were the transverse (n = 23) and sigmoid (n = 22) colon, followed by the hepatic flexure (n = 18) and ascending colon (n = 15). Segments that less frequently accounted for the proximal level reached were the splenic flexure (n = 9), descending colon (n = 4), cecum (n = 4), and rectum (n = 2). For cases of incomplete optical colonoscopy where the cecum was reached or the ileocecal valve was identified, the cecal tip was not completely evaluated. In the three remaining patients, the most proximal level reached was not clearly recorded in the report.
Endoscopists documented multiple reasons for failure to fully intubate the cecum in their report and in some cases recorded more than one reason for a given patient. Examples of the reasons cited included tortuosity or redundancy (n = 37 patients); some combination of fixation, angulation, adhesion, or spasm (n = 30); looping of the scope (n = 18); excessive pain (n = 10); diverticular disease (n = 7); cardiovascular instability (n = 4); poor preparation (n = 4); and occlusive mass (n = 1).
The control group (complete optical colonoscopy) was composed of 100 consecutive asymptomatic average-risk adults (mean age, 58.2 ± 7.9 years; 40 women, 60 men) who underwent sameday CTC and complete optical colonoscopy at a single institution over a 4-month period as part of a screening trial. The CTC and optical colonoscopy performance results of this trial have been previously published [8], but the information regarding colonic anatomy has not.
A polyethylene glycol bowel preparation for optical colonoscopy was generally used for the patients in the incomplete optical colonoscopy study group. Optical colonoscopy examinations for the incomplete study group were performed by experienced gastroenterologists with standard technique and endoscopes (EC-3430L and EC-3830/31L series, Pentax). Patients in the control group underwent bowel preparation consisting of sodium phosphate in conjunction with oral contrast material for stool tagging. This approach was also used for patients with incomplete optical colonoscopy who did not undergo CTC on the same day, although magnesium citrate was substituted for sodium phosphate when indicated. The differences in preparation would not be expected to alter the underlying colonic anatomy.
Colonic distention for CTC was obtained by either automated continuous delivery of carbon dioxide or patient-controlled insufflation of room air. Breath-hold supine and prone CT acquisitions were obtained on 4-, 8-, or 16-MDCT scanners (LightSpeed series, GE Healthcare) using 1.25- to 2.5-mm collimation, 1-mm reconstruction interval, 120 kVp, and 50–100 mAs.
The MDCT data were transferred to a commercial CTC software system (V3D Colon, Viatronix) for interpretation by two experienced gastrointestinal radiologists. The CTC studies were independently reviewed by both radiologists, with discrepancies resolved by an additional consensus review. Data collected included colon length (total, sigmoid colon, and transverse colon); number of colorectal flexures, defined as a focal acute angle (< 90°) bend of the colon; presence of advanced diverticular disease, as previously defined at CTC [9]; and any other identifiable factors that could result in difficult optical colonoscopy examination.
The CTC workstation used in this study produces a 3D map of the large intestine, including an automated centerline that allows precise colonic length measurements. With regard to colonic length measurements at CTC, it should be noted that these measurements are typically much longer than the corresponding optical colonoscopy measurements because of telescoping and straightening that foreshorten the insertion length at optical colonoscopy (Brickman D et al., presented at the 2004 Scientific Assembly of the Radiological Society of North America). Interactive rotational manipulation of the map by the reviewer greatly facilitates assessing the number of flexures. A 2D multiplanar reformation display allows evaluation of diverticular disease. Prone or supine views were used at the discretion of the radiologists; however, both radiologists interpreted the same view for each case.
In addition to age and sex comparisons between the study and control groups, a history of abdominal surgery was also recorded. We did not compare differences in polyp detection at CTC between the incomplete and complete optical colonoscopy groups because the diagnostic utility of CTC after incomplete optical colonoscopy has already been well studied [10, 11]. Statistical testing for comparing differences between the study and control groups was performed using the chi-square test.
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For all CTC data collected, there was generally a highly statistically significant difference between the two patient groups in the study (Table 2). The average total colorectal length was nearly 45 cm longer in the incomplete optical colonoscopy study group compared with the complete optical colonoscopy control group (p < 0.0001). In most cases, patients with complete optical colonoscopy had total colorectal lengths of less than 200 cm, whereas patients in the incomplete optical colonoscopy group tended to have a total length of more than 200 cm, with several cases exceeding 300 cm. Similarly, sigmoid and transverse colonic lengths were significantly longer in the incomplete optical colonoscopy study group than in the control group (p < 0.0001).
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On average, there were more than two additional acute angle colonic flexures in the incomplete optical colonoscopy group compared with the complete optical colonoscopy group (p < 0.0001), ranging from a low of five flexures to as many as 19 flexures in one patient. Advanced colonic diverticular disease was present in 34 patients (34%) in the incomplete optical colonoscopy study group compared with 22 patients (22%) in the complete optical colonoscopy control group, which represents a modest but statistically significant difference (p < 0.05). Diverticular disease was primarily concentrated in the sigmoid and descending colon. Panels of 3D colon maps from CTC representative of incomplete optical colonoscopy and complete optical colonoscopy are shown in Figures 1 and 2, respectively.
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200 cm at CTC, our data predict incomplete optical colonoscopy with a
sensitivity of 58%, specificity of 93%, and accuracy of 75.5%. The positive
predictive value (PPV) in this case is 89.2%, and the negative predictive
value (NPV) is 68.9%. If the threshold for the number of acute angle flexures
is set at 10, our data predict incomplete optical colonoscopy with an
increased sensitivity of 84% but a decreased specificity of 62% compared with
the 200-cm length threshold. Accuracy remains similar at 73%, with a PPV of
68.8% and an NPV of 79.5%. When either a 200-cm total length threshold or
advanced colonic diverticular disease is present, the sensitivity,
specificity, PPV, and NPV are more equally balanced at 79%, 72%, 73.8%, and
77.4%, respectively. |
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Our clinical findings that female sex, increasing patient age, and history of abdominal surgery more likely are to be associated with incomplete optical colonoscopy agree with findings that have been reported previously in the literature [1, 3]. Women with a history of abdominal hysterectomy have also been found more likely to undergo incomplete optical colonoscopy [3], which is similar to our results. A previous study focusing on clinical factors related to incomplete flexible sigmoidoscopy also showed a higher frequency in women, older patients, women who had undergone hysterectomy, and men who had undergone abdominal surgery [4].
Other patient factors shown to be associated with incomplete optical colonoscopy that were not specifically addressed in this study include a BMI of < 25 and a history of constipation or reported laxative use [2, 5]. Interestingly, one study showed that optical colonoscopy itself was not necessarily a highly predictive factor, with 67% of patients with incomplete optical colonoscopy having a history of complete optical colonoscopy and 50% of patients with incomplete optical colonoscopy having a subsequent complete optical colonoscopy [3]. A previous study by Saunders et al. [12] evaluated barium enemas in patients who had undergone a "difficult" optical colonoscopy examination compared with patients who had undergone a technically "easy" optical colonoscopy examination. Significant differences identified on the barium enemas between these two groups included rectosigmoid length, total colonic length, redundancy (defined by the transverse colon reaching the true pelvis on the erect radiograph), and moderate to severe diverticular disease.
In our study, "redundancy" was specifically cited by the colonoscopist as a factor for incomplete examination in nine of the optical colonoscopy reports, and increased transverse colonic length was a common finding at CTC in these patients. In general, our results agree with the increased colonic lengths identified on the barium enema studies among patients with difficult optical colonoscopy. As with our study, diverticulosis has also been shown by others to be correlated with incomplete optical colonoscopy examination [1, 12].
The reported rates for complete optical colonoscopy examination have ranged widely from 57% to more than 99.4% [1, 3, 5, 8, 13, 14]. An incomplete optical colonoscopy examination can result in missed cancerous tumors if additional tests for completion are not obtained. One recent study found that optical colonoscopy missed 17 (5.9%) of 286 cancers and that more than half of those patients had had an incomplete optical colonoscopy examination [15]. Alternative structural colorectal examinations such as CTC or barium enema can serve as useful adjuncts after an incomplete examination in this setting. When available, CTC is the preferred test to complete colonic evaluation because of its improved diagnostic performance and greater patient acceptance compared with barium enema [10, 11, 16, 17]. A study by Neri et al. [11] involving 34 symptomatic patients with incomplete optical colonoscopy showed that CTC allowed identification of 13 cancerous colon tumors missed at optical colonoscopy, only three of which were synchronous tumors.
The results of our study have practical implications because patients are increasingly undergoing CTC both for evaluation after incomplete optical colonoscopy and for primary screening. In addition, these results may help address areas for technical improvement at optical colonoscopy. For patients referred for optical colonoscopy after positive CTC findings, the interpreting radiologists should communicate potentially significant anatomic findings to the colonoscopists, such as an increased colon length, increased tortuosity (indicated by an increased number of flexures), or advanced diverticular disease. This information can help the colonoscopists prepare for the challenge and may influence their choice of equipment.
A number of optical colonoscopy studies have evaluated the use of different scopes to help complete the examination in difficult-to-examine patients. For example, one study of 16 patients found that using a variable-stiffness colonoscope enabled completion of optical colonoscopy in 15 of these patients, or 94% [18]. Other options include using pediatric variable-stiffness colonoscopes and smallcaliber, variable-stiffness colonoscopes that have outer diameters of 11.5 and 10.5 mm, respectively, compared with 12.0 mm for the standard adult colonoscope. Another study found that of 52 patients who had an incomplete optical colonoscopy examination when a standard adult colonoscope was used, the examination could be completed in 51 patients after the standard colonoscope was switched to a small-caliber, variable-stiffness colonoscope [14]. Gastroscopes have also been used in the setting of incomplete optical colonoscopy; however, the cecal intubation rate in one study was only 65% [19]. Enteroscopes can also be useful for reaching the cecum in patients with elongated colons [20].
There are several limitations to our study. The incomplete optical colonoscopy study group included a number of symptomatic patients, whereas the complete optical colonoscopy control group did not, leading to possible selection bias. A small number of CTC examinations from the incomplete optical colonoscopy cases were excluded because the centerline on the 3D map did not reflect the true colonic length. In these cases, the colon tended to be extremely tortuous and elongated and likely would have led to even greater anatomic differences between the two groups. We did not evaluate colonoscopist factors such as training and experience, equipment used, and specific techniques used. However, others have shown that cecal intubation rates tend to increase with increasing endoscopist experience and procedural volume [6, 7].
As we discussed earlier, there are a variety of endoscopes that may be used in the difficult-to-examine patient. One final limitation to our study is that there was a somewhat subjective nature to the grading of colonic diverticular disease and to the determination of flexures. It is possible that lesser degrees of diverticular disease could lead to difficulties at optical colonoscopy. Defining a colonic flexure according to acute angles also excludes lesser bends and kinks from consideration, which could also conceivably contribute to difficulty at optical colonoscopy.
In conclusion, we found a number of identifiable anatomic features at CTC that are associated with an increased likelihood of failure to intubate the cecum at optical colonoscopy. These predictive features include elongation (increased colonic lengths), tortuosity (increased number of flexures), and advanced diverticular disease. These CTC findings have potential implications for any future optical colonoscopy examination in these patients and should be communicated to the colonoscopist. These observations may also help in the development of improved training and techniques for completing optical colonoscopy examination in difficult cases.
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