3426 Spectrophotometry of colonic wall: which layers influence surface color on colonoscopy?

Abstract

Background: Colonic surface color on endoscopy is largely determined by hemoglobin content in the colonic tissue, which has been calculated from spectral reflectance of the colonic surface as an index of hemoglobin (IHB). Histological colonic layers, influencing the surface reflectance has, however, still remained undetermined. Aims: The aim of this study was to determine the colonic layers, which influence the surface reflectance and the relative IHB against the total IHB in each colonic layer. Methods: Colonic tissue specimen with a gradation of thickness was constructed by using normal parts of resected colon from 5 patients with colorectal cancer. By using a spectrophotometer, spectral reflectance (410 to 690 nm) was measured at sampling points along a line of interest on the specimen at every 1mm intervals for IHB, which is give by 32Log (r650/r569). r650 and r569 designate reflectance at a wavelength of 650 and 569 nm, respectively. After photometry, the specimen was fixed in 10% formalin and sliced along the line of interest for a thickness of histological layers (micro-meter) in each sampling site. Results: IHB linearly increased to reach plateau as a thickness of the submucosa increased (Table). When a thickness of the submucosa exceeded 400 micro-meter, IHB remained constant, regardless of the presence or absence of deeper layers (propria muscle, subserosa and serosa). A thickness of the mucosa was found to have only least influence on IHB. The relative IHB against the total IHB was less than 45% for the mucosa and the remaining more than 55% for the submucosa. Conclusions: On colonoscopy, surface color was determined exclusively by the mucosa (45%) and submucosa (55%). In spectroscopy, it should be cautious to interpret IHB exclusively as mucosal hemoglobin especially in normal colon.