Transabdominal sonographic appearance of adult colonic polyps

To assess the ability of transabdominal ultrasound to detect adult colonic polyps and to describe their ultrasonographic appearance.

Total colonoscopy was carried out for 729 consecutive patients over a 39-month period. Ultrasonographic examination of the abdomen was followed by specific examination of the colon. Colorectal ultrasound was carried out for patients with colonic polyps of the protruded type (exclusive of advanced cancers and polyps of the flat or depressed types), and cleansing liquid was administered preparatory to colonoscopic examination. In examining colonic polyps we wanted to determine the sensitivity and specificity of ultrasound for detecting colonic polyps, and the presence of power-Doppler flow signals, location, morphologic classification, and size of the polyps.

Ultrasound identified no colonic polyps less than 10 mm in diameter in any of the 729 patients. Of the 732 deternimation (three patients had two polyps greater than 10 mm in diameter), ultrasound yielded a positive diagnosis in 16 cases, false-positive in four cases, false-negative in 40 cases, and negative in 672 cases. Sensitivity of the technique was 28.6% and specificity was 99.4% for detection of polyps greater than 10 mm in diameter. Doppler signals were detected in all positive cases. Most polyps that were false-negatives on ultrasound examination occurred in the rectum and sigmoid colon. Sensitivity increased with tumor size, and was as high as 82% (9/11) for polyps exceeding 25 mm in diameter. Fifty-seven percent of pedunculated polyps (type Ip) but no sessile polyps (type Is) were found using ultrasound.

Colorectal ultrasound detected adult colonic polyps greater than 10 mm in diameter 16 of the 56 in present 729 patients, suggesting that this method may be of limited value in screening for colonic polyps.