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Original Research |
1 All authors: Department of Radiology, Thomas Jefferson University Hospital, 132 S 10th St., Main Bldg., Ste. 763L, Philadelphia, PA 19107.
Received May 17, 2007;
accepted after revision July 18, 2007.
A. S. Lev-Toaff is a consultant for Philips Medical Systems.
Abstract
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MATERIALS AND METHODS. Over a 2-year period, 61 patients underwent CTC at our institution, 42 of whom (26 women, 16 men) were 60 years old or older (range, 60-87 years; mean age, 71 years). After 24-48 hours of ingesting only clear liquids and after colonic cleansing, fecal tagging, and automated CO2 insufflation, patients were scanned using a 16-MDCT scanner. Images were obtained with the patient in the supine and prone positions and as needed in the right or left decubitus position. Axial 2D and 3D endoluminal views were evaluated on a dedicated workstation.
RESULTS. Contraindications to colonoscopy in 12 (29%) of the 42 patients were as follows: anticoagulation (n = 8), increased anesthesia risk (n = 3), and poor tolerance for colonoscopy preparation (n = 1). Incomplete colonoscopy in the other 30 patients (71%) was due to diverticular disease (n = 10), colonic redundancy (n = 10), adhesions (n = 3), residual colonic content (n = 3), sigmoid stricture (n = 1), ventral hernia (n = 1), and unknown cause (n =2). No complications were observed. Optimal distention of the entire colon was achieved in 38 patients (90%). Thirty-nine (93%) of the 42 patients had abnormal findings: diverticular disease (n = 25), one or more polyps (n = 22), a mass lesion (n = 1), a lipoma (n = 1), and inflammatory stricture (n = 1). Extracolonic findings potentially requiring further evaluation or treatment were observed in 26 patients (62%).
CONCLUSION. CTC using CO2 insufflation was well tolerated and successful in imaging the entire colon in most of the 42 patients, despite the presence of sigmoid diverticular disease or colonic redundancy.
Keywords: colorectal cancer • CT colonography • double-contrast barium enema • elderly patients • optical colonoscopy
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Optical colonoscopy is the standard method for evaluating the colon [3, 4]. This technique allows evaluation of the entire colon in most patients. Also, biopsy of suspicious lesions and polypectomy may be performed during colonoscopy. However, colonoscopy is invasive, requires patient sedation, and is not accepted by all patients. Even when performed by experienced endoscopists, approximately 6-26% of colonoscopic examinations are incomplete and fail to reach the level of the cecum [5, 6]. The reasons for incomplete colonoscopy are redundant or tortuous colon, marked diverticular disease, obstructing masses and strictures, angulation or fixation of colonic loops, adhesions due to prior surgery, spasm, or poor colonic preparation [7]. Colonoscopy requires intensive bowel preparation that many patients find to be the most difficult part of the test and that some cannot tolerate [8]. In patients with medical conditions that result in increased sedation risk (e.g., cardiovascular or pulmonary disease) or in those being treated with anticoagulants, a less invasive technique for evaluation of the colon might be preferred to minimize the risk for possible complications.
The number of incomplete colonoscopies and contraindications tends to increase in elderly patients. In elderly patients, the rate of incomplete colonoscopies has been reported to be as high as 22-33% [9]. When colonoscopy cannot be performed or the examination is incomplete, alternative techniques, such as colonoscopy with thinner colonoscopes or gastroscopes, barium enema, CT colonography (CTC), and MR colonography, may be preferred [10].
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The purpose of our study was to assess the performance of CTC in older patients who were referred because colonoscopy either could not be performed due to contraindications or had been performed but was incomplete.
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Twelve (29%) of the 42 patients were referred to undergo CTC because colonoscopy was contraindicated for the following reasons: anticoagulation therapy (Fig. 1A, 1B, 1C, 1D), increased anesthesia risk, or poor tolerance for colonoscopy preparation. CTC was performed in 30 (71%) of the 42 patients because colonoscopy was incomplete due to sigmoid diverticular disease, colonic redundancy (Fig. 2), adhesions, residual colonic content, sigmoid stricture, ventral hernia, and unknown cause. The contraindications for optical colonoscopy and the reasons for incomplete colonoscopies are listed in Table 1. In seven patients, a barium enema had been performed or attempted but was unsuccessful or incomplete.
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Images were obtained with the patient in the supine and prone positions and, when needed to optimally distend the right or left colon, in the right or left lateral decubitus position. All examinations were closely monitored by one of two body imaging radiologists who assessed colonic distention and determined the need for imaging in addition to imaging with the patient supine and prone. Two-dimensional images in the axial, coronal, and sagittal planes and volume-rendered 3D endoluminal views were evaluated on a dedicated 3D workstation (Brilliance, Philips). Images were interpreted using a primary 3D evaluation by a single radiologist with extensive experience in body imaging and 2 years of experience interpreting CTC; this radiologist was one of the two radiologists who monitored the acquisition of the data.
Colonic polyps that were 5 mm or larger in diameter were recorded. The presence of diverticular disease was noted and graded by severity. Extracolonic findings were noted and categorized into two groups on the basis of clinical importance: high and low clinical importance. A high-clinical-importance finding was defined as one that potentially requires further radiologic investigation, follow-up, medical treatment, or surgical treatment, such as indeterminate mass lesions, gallstones, renal stones, hydronephrosis, enlarged lymph nodes, and aortic aneurysm. A low-clinical-importance extracolonic finding was defined as an incidental finding that does not require further investigation or that is unlikely to require medical treatment (e.g., vascular calcifications, bone degeneration, hiatal hernia, simple cysts, and so on). Institutional review board approval was obtained for this retrospective study.
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In 38 (90%) of the 42 patients, adequate distention of the entire colon was achieved (Fig. 3A, 3B, 3C). In the remaining four patients, adequate distention of the entire colon could not be achieved due to spasm (n = 2), sigmoid stricture (n = 1), or compression of the transverse colon located within a large anterior abdominal wall hernia (n = 1). In two patients, abundant reflux of gas into the small bowel was observed because of ileocecal valve incompetency, but adequate colonic distention was achieved. No complications were encountered during or after the CTC examinations.
CTC showed that 39 (93%) of the 42 patients had positive findings, with patients often having more than one finding each: 25 patients had mild to extensive diverticular disease, and five had diverticulosis without distortion of the colonic lumen. In 22 patients, one or more polyps were identified (total number of polyps, 43; mean diameter, 9 mm; range, 5-15 mm; 12 polyps > 10 mm); one patient had a polypoid mass lesion greater than 3 cm in diameter, one had a lipoma, and one had a sigmoid inflammatory stricture. The CTC findings are listed in Table 2. In five (23%) of the 22 patients with polyps, optical colonoscopy was performed after CTC; in these five cases, seven polyps were removed. Histopathologic diagnoses were adenomatous polyp (n = 3) and hyperplastic polyp (n = 4). The remaining 17 patients with polyps on CTC are being observed clinically and have not undergone optical colonoscopy.
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Extracolonic findings were identified in 39 (93%) of the 42 patients. High-clinical-importance extracolonic findings were seen in 26 patients (62%), whereas low-clinical-importance extracolonic findings were encountered in 36 (86%) (Table 3). The total number of findings in Table 3 is greater than 42 because many patients had more than one finding.
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To increase the rate of cecal evaluation and complete colonoscopic examinations, some researchers have reported using gastroscopes or small-caliber, variable-stiffness colonoscopes [13, 14]. Paonessa et al. [13] used a gastroscope for incomplete colonoscopy and achieved cecal intubation in 16 (62%) of 26 incomplete cases. Horiuchi et al. [14] completed colonoscopic examinations in 51 (98%) of 52 patients with a prior incomplete study by using a small-caliber, variable-stiffness colonoscope.
Double-contrast barium enema (DCBE) has been used to image the colon after failed or incomplete colonoscopy. If DCBE is used immediately after colonoscopy, the patient does not need to undergo a second bowel preparation. In 77-94% of patients, visualization of the entire colon may be achieved by performing DCBE immediately after colonoscopy [15, 16]. Success rates for immediate DCBE may be influenced by the age and mobility of the patient, enema technique, and degree of sedation for colonoscopy. Older patients may find it difficult to tolerate a DCBE examination after sedation. Also, excessive intraluminal air or fluid from same-day optical colonoscopy may prevent colonic filling and mucosal coating with barium. This limitation may be more problematic in older patients with redundant colons.
CTC, or virtual colonoscopy, is a relatively new imaging technique that was first described in 1994 (Vining DJ, Gelfand DW, presented at the 23rd annual meeting and postgraduate course of the Society of Gastrointestinal Radiologists) and became commercially available in 1995. The major advantage of CTC over conventional cross-sectional imaging is visualization of the endoluminal surface by distention of the colon and 3D reconstruction of colonic anatomy. CTC is currently performed on the cleansed colon in a manner optimized for the detection of polyps and masses. Fecal tagging may be used to assist in the discrimination of fecal residue from true mucosal lesions. After an enema tube is inserted into the rectum, room air or CO2 is insufflated using either a manual technique with a hand bulb or a mechanical insufflator with which pressure is controlled. The routine use of an antispasmodic agent is not favored because it can result in excessive reflux of gas through the ileocecal valve and make it more difficult to evaluate the colonic segments.
After sufficient distention is observed on the scout view, CTC with the patient in both prone and supine positions is performed. In some cases, scanning in the right or left lateral decubitus position may be helpful to move retained fluid and optimize colonic distention. Each scan is acquired in approximately 30-40 seconds. The total room time is generally less than 15 minutes. The data are sent to a workstation, and with the use of special software, 2D images in multiple planes and 3D surface-rendered and endoluminal views are displayed. In our practice, 3D endoluminal views and 2D multiplanar reformations are displayed side by side on two monitors to facilitate rapid interpretation; we use 3D navigation for primary detection of focal abnormalities and correlation with 2D multiplanar images to determine the nature of a focal finding.
From institution to institution, techniques for patient preparation and examination differ. In our study group, patients with a history of constipation or poor preparation results on previous testing ingest only clear liquids for 48 hours before CTC. Also, we closely monitor each examination to optimize our technique and diagnostic results. This protocol proved to be important in the examination of older patients with redundant and distorted colons who have had incomplete colonoscopies. Because of the prevalence of sigmoid diverticular disease in our patients, right lateral decubitus imaging was used liberally, in 81% of our patients, to optimize visualization of the left colon. We used fecal tagging with barium sulfate suspension in all patients. Given the prevalence of diverticular disease in the older patients in our study, we found that fecal tagging was useful for prompt identification of fecaliths and fecal residue in narrowed and distorted sigmoid colons. In the future, technical innovations will make colonic cleansing less important and CTC even more useful for the examination of older patients [17].
In our series of older patients, adequate distention was achieved in 90% of the patients in at least one of the positions using automated CO2 insufflation. This finding is similar to the results reported by Mingyue et al. [18], who achieved colonic distention in 91.7% of patients, ranging in age from 20 to 78 years, who had previously undergone incomplete colonoscopy. Our patients were scanned using 16-MDCT; the scanning duration required breath-holding of 30-40 seconds, which was generally well tolerated. Motion artifact was not a major problem, although a patient was rescanned occasionally because he or she did not hear the instructions. As MDCT scanners evolve further, respiratory motion artifacts should become less problematic and even thinner image reconstructions will result in improved radiologist confidence in CTC interpretation [19].
With CTC, an unenhanced CT examination of the entire abdomen and pelvis is performed. Unlike optical colonoscopy or barium enema, this examination provides the advantage of imaging all the intraabdominal structures simultaneously, and incidental extracolonic findings can be observed. In several series, these extracolonic findings were classified according to their clinical importance, with their prevalences provided. The overall prevalence of extracolonic findings varied from 15% to 85%, whereas the prevalence of highly important findings ranged from 4.5% to 13% [20]. Dachman [21] reported 26 extracolonic findings in 44 patients, only one of which (a 3-cm adrenal mass) resulted in additional workup. In a group of 40 patients with incomplete colonoscopy, Morrin et al. [22] reported significant extracolonic findings, such as aortic aneurysm, complex ovarian cyst, and obstructing ventral hernia, in 13% of patients. Hopper et al. [23] reported potentially significant extracolonic findings in 10 (10%) of 100 patients and insignificant extracolonic findings in 80%.
Previously undiagnosed extracolonic malignancies at CTC are likely to increase with patient age. In one series of more than 1,000 patients with an average age of 80 years, the prevalence of previously undiagnosed malignancies was more than twice as high as the prevalence for groups in other studies [24]. In our series, the prevalence of extracolonic findings (93%) was higher than has been reported in other series. The high prevalence of low-clinical-importance extracolonic findings (86%) in our study is primarily because of vascular calcifications, bone degenerative changes, and simple renal cysts. All of these findings are commonly observed in older patients and do not need further investigation. However, the prevalence of high-clinical-importance extracolonic findings was also greater (62%) in our series than in most other series. This was mainly due to a high rate of indeterminate lesions such as pancreatic, renal, adrenal, and ovarian masses and complex renal or hepatic cysts.
In this study, we defined "high-clinical-importance extracolonic findings" as findings potentially requiring further evaluation or follow-up. We included findings such as gallstones and renal stones, although some authors have categorized those findings as not clinically important. Many of our patients were referred from outside institutions, and we did not have access to previous imaging records to determine whether these findings had been previously documented or were of clinical significance. A potential advantage of performing CTC as opposed to barium enema in older patients with incomplete colonoscopies is that clinically important extracolonic findings may be identified; some of these findings could potentially explain the patient's symptoms.
CTC also has some inherent limitations. Flat lesions may be more difficult to detect with CTC [25, 26] because the conspicuity of flat lesions on 3D endoluminal imaging is diminished; varying soft-tissue window settings and using fecal tagging may help to improve detection [26]. Visualization of the true color of the mucosa can be helpful for the identification of flat lesions. However, in CTC, colors are assigned arbitrarily. The presence of a thickened wall may be a helpful finding, but when this finding is seen, the lesion is generally already large.
Another limitation of CTC is the lack of information about hyperemia, inflammatory infiltration, and mucosal erosion. MR colonography or the use of more specific contrast agents with CTC may provide more information about these functional changes. The most significant limitation of CTC is that it is unable to provide a pathologic specimen. When an additional lesion is found with CTC after optical colonoscopy is incomplete, the necessary pathologic proof about the nature of the lesion is still needed. Likewise, findings on CTC may need to be followed up for growth or to be pursued with optical colonoscopy even in patients with risk factors and contraindications.
In conclusion, CTC with fecal tagging and CO2 insufflation is well tolerated by older patients and was successful in imaging the entire colon in most patients, despite the presence of advanced sigmoid diverticular disease and colonic redundancy. As MDCT technology improves further and automatic cleansing software becomes available, CTC should become even more feasible and be readily tolerated by older patients.
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