Level 2: Mid-level evidence
A cross-sectional cohort study evaluated 1,819 patients (96% male, mean age 64 years) who had elective colonoscopy at a veterans’ hospital (JAMA. 2008;299:1027-1035). Commercially available high-resolution adult colonoscopes were used, and 0.1%-0.4% diluted indigo carmine 10-25 mL was sprayed though the accessory channel if nonpolypoid colorectal neoplasms were suspected. Patients were stratified to three groups based on indication for the procedure: 34% screening, 36% surveillance (patients with a personal or family history of colorectal neoplasm or cancer), and 30% symptoms possibly due to neoplasm (anemia, rectal bleeding, diarrhea, positive results from a fecal occult blood test, weight loss, abdominal pain, or inflammatory bowel disease).
The prevalence of nonpolypoid colorectal neoplasm was 9.35% (170 patients): 5.84% in screening group, 15.44% in surveillance group, and 6.01% in symptomatic group. Among 2,770 lesions found (neoplastic and nonneoplastic), 11% (307) were nonpolypoid. Invasive cancer or carcinoma in situ was found in 13 of 2,463 (0.5%) polypoid lesions and 15 of 307 (4.9%) nonpolypoid lesions. Among the nonpolypoid lesions, invasive cancer or carcinoma in situ was found in nine of 289 (3.1%) flat lesions and six of 18 (33%) depressed lesions.