Background and study aims: Depressed early cancers and flat adenomas have a high potential for malignancy with possible infiltrating growth, despite the small size of the lesion. Japanese investigators have shown that early diagnosis and classification of these lesions is possible with the help of chromoendoscopy. The aim of this study, therefore, was to evaluate the usefulness of chromoendoscopy during routine colonoscopy.
Patients and methods: During routine colonoscopy, vital staining with indigocarmine solution (0.4 %, 1 - 10 ml) was performed on all visible lesions in 100 consecutive patients without visible inflammatory changes. If findings on macroscopic examination were unremarkable, the sigmoid colon and rectum were stained with indigocarmine over a defined segment (0 - 30 cm ab ano) and inspected for lesions visible only after staining. Each lesion was classified with regard to type (polypoid, flat, or depressed), position and size. The staining pattern was classified according to the pit pattern classification.
Results: A total of 52 patients had 105 visible lesions (89 polypoid, 14 flat and two depressed). The mean size of the lesions was 1.4 cm. Among the 48 patients with mucosa of normal appearance, 27 showed 178 lesions after staining (176 flat, two depressed) with a mean size of 3 mm. On histological investigation, 210 lesions showed hyperplastic or inflammatory changes, 67 were adenomas and six were cancers. Use of the pit pattern system to classify lesions (adenomatous, pit patterns III-V; nonadenomatous, pit patterns I-II) was possible, with a sensitivity of 92 % and a specificity of 93 %. Lesions with pit patterns III - V showed higher rates of dysplasia.
Conclusions: Chromoendoscopy allows easy detection of mucosal lesions in the colon and facilitates visualization of the margins of flat lesions. This technique unmasks multiple mucosal lesions which are not identified by routine video colonoscopy. The pit pattern seen after staining allows differentiation between hyperplastic and adenomatous lesions which may have consequences with regard to the endoscopic interventions needed.