Is Chromoendoscopy with Indigo Carmine, Without a Magnifying Colonoscope, Accurate in the Differential Diagnosis of Colorectal Polyps ≤10 mm in Size?

Abstract

Introduction: chromoendoscopy with magnifying colonopy is accurate (>90%) in the differential diagnosis of small colorectal polyps; however, few studies have addressed the accuracy of indigo carmine with a standard video-colonoscope. Aim: to assess the diagnostic accuracy of chromoendoscopy with indigo carmine and conventional colonoscopy in the differential diagnosis of small (≤10 mm) colorectal polyps. Methods: 788 polyps detected by colonoscopy in 703 patients were prospectively included; 200 (25.3%) were excluded due to a lack of a histological diagnosis, a size >10 mm, or the presence of a malignant polyp. Indigo carmine (0.2%) was applied to each polyp by syringe, and the crypt pattern was assessed according to Fujii's classification as, non-invasive, neoplastic non-invasive, and neoplastic-invasive. In indeterminate cases, the pattern was diagnosed as indefinite. The lesions were classified according to their shape as flat or protruding following the standards of the Japanese Research For Cancer of Colon and Rectum Classification. Sensitivity (SE), specificity (SP) and diagnostic accuracy (DA) in the diagnosis of neoplastic polyps, were calculated globally, and separately for flat and protruding lesions. Results: 588 lesions were included (30.1% flat, 69.9% protruding), among these 68.4% were adenomatous. The crypt pattern was indefinite in 12.8%, non-neoplastic in 24.2%, and neoplastic non-invasive in 63.0%. In 65.4% indefinite-pattern cases, the lesion was neoplastic. Globally, the SE, SP and DA were 78.7%, 57.3% and 71.9% respectively. For flat lesions, SE, SP and DA were 76.0%, 67.0% and 72.3%, whereas for protruding lesions SE, SP and DA were 76.2%, 49.0% and 71.7% respectively. Conclusions: chromoendoscopy with indigo carmine and conventional colonoscopes cannot accurately differentiate between small neoplastic and non-neoplastic polyps, leaving 23% of the adenomas unrecognized.