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Background Hydrocolonic ultrasonography -- abdominal ultrasonography in conjunction with the retrograde instillation of water into the colon -- has been advocated as an alternative to colonoscopy for detecting colorectal polyps and cancer. We conducted a prospective, blinded trial to evaluate the procedure further.
Methods Fifty-two consecutive patients (50 men and 2 women; average age, 62 years) who were referred for colonoscopy underwent hydrocolonic ultrasonography followed by colonoscopy. The physicians performing colonoscopy were blinded to the ultrasound results. Patients who had a history of colonic polyps or tumors or who had previously undergone flexible sigmoidoscopy or colonoscopy were excluded.
Results Twenty-two patients had normal results on colonoscopy, 26 had polyps, 3 had cancer and polyps, and 1 had cancer alone. Twenty patients had polyps less than 7 mm in diameter, eight had polyps 7 mm or more in diameter, and one had a polyp of unknown size. Hydrocolonic ultrasonography did not detect any cancers and detected only one polyp
Conclusions Hydrocolonic ultrasonography was less useful than colonoscopy for detecting colorectal polyps and cancers. The usefulness of the technique in screening for colonic polyps and tumors appears to be limited.
7 mm and one polyp <7 mm in diameter. The overall sensitivity of ultrasonography for identifying any polyp was 6.9 percent, and for identifying a polyp 7 mm, it was 12.5 percent. Ultrasonography suggested the presence of five masses and five polyps that were not confirmed by colonoscopy. Six patients had incomplete ultrasound studies because of discomfort or the inability to retain water. There were two complications: one patient had two vasovagal episodes, and another had diaphoresis.
7 mm in diameter.2 In addition, detailed evaluation of the structure of the colonic wall was reported to permit a more precise staging of colonic tumors. We conducted a prospective, blinded trial to evaluate further the diagnostic usefulness of this procedure. Methods
We studied 52 patients (50 men and 2 women) referred consecutively for colonoscopy to the gastroenterology service at the San Francisco Veterans Affairs Medical Center. Twenty-four patients had a positive screening test for fecal occult blood, 6 had iron-deficiency anemia, 14 had hematochezia, and 8 had other indications for colonoscopy, such as nonspecific anemia, abdominal pain, change in bowel habits, or a family history of colon cancer. Patients with histories of colonic polyps or tumors, flexible sigmoidoscopy or colonoscopy, or colonic polypectomy were excluded. The study was approved by the Human Research Committee of the University of California, San Francisco; written informed consent was obtained from each participant.
On the day before the examinations, oral intake was limited to clear liquids, and each patient began to ingest 4 liters of an electrolyte solution (Colyte, Reed and Carrick, Jersey City, N.J.). The patients fasted after midnight. Immediately before colonoscopy, hydrocolonic ultrasonography was performed under the direct supervision of one of two board-certified radiologists with 10 to 30 years of ultrasound experience. Ultrasonography was performed in a fluoroscopy suite with an Acuson 128XP device (Acuson, Mountain View, Calif.) and a commercial barium-delivery system; warm water was substituted for barium in the plastic bag and tubing. To prevent the loss of water after instillation, a plastic balloon catheter was inflated in the rectum under fluoroscopic guidance. The patient's position was adjusted with a tilting table. Patients received an intramuscular injection of either 1 to 2 mg of glucagon (47 patients) or 1 to 2 mg of hyoscyamine sulfate (Levsin, Schwarz Pharma, Milwaukee) (5 patients) to relax the colon.
A total of 1 to 2 liters of water was instilled into the colon, as follows. With the patient upright, 300 to 500 ml of water was instilled transrectally to fill the sigmoid colon. The patient was then placed supine, and the remaining water was instilled. Patients were turned to the right and left to fill the colon with water and reduce the shadowing effects of air in the lumen of the colon. Continuous transabdominal colonic ultrasonography began at the time of instillation, with a real-time scanning device with 3.5-, 5.0-, and 7.0-MHz transducers. Color Doppler (Acuson) was used to evaluate vascularity in an attempt to differentiate stool from neoplasm.
Immediately after hydrocolonic ultrasonography was completed, colonoscopy began. This examination was performed by gastroenterology fellows under the direct supervision of board-certified staff gastroenterologists. The colonoscopists were blinded to the results of the ultrasound examinations. The ultrasonographic diagnosis of colonic tumors was based on evidence of intraluminal masses fixed to the wall of the colon. All polyps identified at colonoscopy were excised, measured, and examined histologically. Colonic tumors that could not be resected through the colonoscope were removed surgically and examined histologically. The pathological stage of the tumor was compared with the stage as determined by ultrasonography.
Results
Fifty-two patients were studied; an additional eight eligible patients declined to participate. The average age of the patients was 62 years. All colonoscopic examinations reached the cecum. Twenty-two patients had normal results (Table 1). There were 26 patients with polyps, 3 with cancer and polyps, and 1 with cancer alone. The 29 patients with polyps had a total of 66 polyps. Twenty patients had polyps <7 mm in diameter, and eight had polyps 7 mm. In one patient, a polyp was lost during retrieval and could not be measured. Of the four patients with cancer, three had polyps 7 mm. Three patients with cancer underwent laparotomy with resection of the lesions. Two patients had Dukes' stage B2 lesions, and one had a Dukes' stage C2 lesion. The fourth patient with cancer had carcinoma in situ in a polyp that was completely resected during colonoscopy. There were no complications of colonoscopy.
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7 mm (Figure 1), and one polyp <7 mm. Hydrocolonic ultrasonography suggested the presence of five masses and five polyps in 10 of the 52 patients, findings that were not confirmed by colonoscopy (false positive rate, 19.2 percent). Six patients had incomplete ultrasound studies because they were unable to retain water or had abdominal discomfort. There were two complications: one patient had two vasovagal episodes, and another had diaphoresis after the instillation of water. In these instances, the procedure was terminated. The rectum was not visualized by hydrocolonic ultrasonography in any patient. Hydrocolonic ultrasonography did not permit a reliable examination of the entire colon in 34 patients (poorly visualized regions included the sigmoid colon in 23 patients, the transverse colon in 14, the splenic flexure in 10, and the hepatic flexure in 7). In addition, the depth of intramural lesions could not be reliably documented. The average duration of the hydrocolonic ultrasound examinations was 25 minutes, as compared with about 15 minutes in a prior report.1 The overall sensitivity of hydrocolonic ultrasonography for identifying any polyp was 6.9 percent, and for detecting polyps 7 mm in diameter it was 12.5 percent.
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Our experience with hydrocolonic ultrasonography was not favorable. One of the main technical difficulties related to the body habitus of the patients. In obese patients, it was not possible to obtain good visualization of the colon with 5.0- or 7.0-MHz ultrasound transducers, because of poor depth penetration. We therefore had to use a lower-frequency (3.5-MHz) transducer, and the resolution and ability to distinguish fecal material from lesions were poor. In the case of one obese patient (weight, 145 kg) who was found to have 17 polyps at colonoscopy, we were unable to identify any polyps with ultrasound. Previous reports1,2 have not specified the body habitus of the patients. In our study 16 patients (30.8 percent) weighed more than 90 kg.
The success of hydrocolonic ultrasonography relies heavily on the preparation of the colon. Although all the patients underwent a standard preparation for colonoscopy, some had adherent stool that was difficult to differentiate from colonic lesions. Stool can appear as multiple hyperechoic mobile reflections in an ultrasound examination (Figure 2), or as focal masses adhering to the colonic wall. It may be associated with acoustic shadowing, but it has no vascularity on color Doppler examination. Attempts to move adherent stool by instilling more water, by applying pressure with the ultrasound transducer, and by changing the patient's position were often unsuccessful. In our experience, color Doppler did not distinguish between stool and neoplasm. All the masses we identified by hydrocolonic ultrasonography were avascular.
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Air scatters the acoustic beam. Bowel gas therefore caused difficulties in evaluating the colon with hydrocolonic ultrasonography, even after the patient had been repositioned. In some patients, colonic redundancy made it more difficult to follow the entire length of the colon. Although a transverse view can help verify colonic lesions, overlying air pockets can interrupt the continuity of the colon and make it difficult to follow transversely. In one case, a large lateral cecal carcinoma was missed that could theoretically have been seen in the transverse plane. Much of the examination was performed in the longitudinal plane because it was easier to find and trace the colon than in the transverse plane.
It is possible that the skills and experience of the ultrasonographers contributed to the limited usefulness of hydrocolonic ultrasonography, but we believe this to be very unlikely. The examiners were board-certified radiologists with extensive experience in all aspects of ultrasonography, including endoscopic, transrectal, transvaginal, and vascular techniques. Although instilling water into the colon and then examining the colon under ultrasound guidance was a new procedure, the concept is familiar to radiologists who routinely perform barium enemas. Ultrasonographers have experience evaluating fluid-filled bowel and the abnormalities related to thickening of the bowel wall. During this study, there was no improvement in the visualization of polyps and cancers in the patients examined later as compared with those enrolled earlier, suggesting that increasing experience did not affect the results.
The large discrepancy between our findings and the findings in prior reports1,2 may be attributable to differences in the groups of patients studied. Many of our patients were obese and had redundant colons; these characteristics may increase the frequency of some of the problems we encountered. Nevertheless, a procedure that is sensitive only in certain groups of patients has limited usefulness for general screening. It is noteworthy that we enrolled a considerably smaller number of patients than the previous studies. However, studying more patients, particularly with a technique that has many false positive findings, a low sensitivity, and a substantial number of complications, would not be likely to alter our conclusions. In fact, we terminated the study because of the limited usefulness of hydrocolonic ultrasonography and to avoid further complications.
In conclusion, we found that hydrocolonic ultrasonography was less useful than colonoscopy for detecting colorectal polyps and cancers in a group of patients who were predominantly older men. The sensitivity of the procedure may be greatest in persons with thin body habitus and excellent bowel preparation. Although the results may be acceptable in selected circumstances, we doubt that hydrocolonic ultrasonography is in general an effective screening procedure for colorectal polyps and cancers.
Supported by a grant (DK07007) from the National Institutes of Health.
We are indebted to Dr. Martin Heyworth for editorial suggestions and assistance and to Dr. Jerry Winniczek for help in preparing the manuscript.
Source Information
From the Departments of Medicine (D.W.C., K.R.M., J.H.G.) and Radiology (G.A.W.G., V.G.), University of California and Veterans Affairs Medical Center, San Francisco.
Address reprint requests to Dr. Chui at the Gastroenterology Section (111B), San Francisco VA Medical Center, 4150 Clement St., San Francisco, CA 94121.
References
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Related Letters:
Hydrocolonic Ultrasonography
Limberg B., Gooding G. A.W., McQuaid K. R., Chui D. W.
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Full Text
N Engl J Med 1995;
332:1581-1582, Jun 8, 1995.
Correspondence
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