胃癌―内視鏡診断の最先端

Recent Advances in the Endoscopic Diagnosis of Early Gastric Cancer

　適応型構造強調および適応型IHb色彩強調併用処理は，早期胃癌の浸潤範囲診断に有用であった．特に胃体部を観察する際に，ある一定の褪色域を指標に未分化型癌の存在診断や浸潤範囲の正確な診断に有用になることが期待される．狭帯域フィルター内視鏡(narrow band imaging ; NBI)システムとは，面順次式電子内視鏡のRGBそれぞれに従来と異なる狭帯域フィルターを用いた光源装置である．NBI併用による拡大電子内視鏡観察により早期胃癌の各組織型における粘膜内癌の特異的な毛細血管パターンが認識できる可能性が高いと考えられた．また粘膜微細構造と毛細血管模様を把握することにより，微小癌とびらんの鑑別，癌浸潤範囲の同定困難例の診断に応用可能である．

　With the adaptive index of hemoglobin (IHb) color enhancement processing technology, the intensity of enhancement can be selected for each pixel, corresponding to the brightness level of the pixel. We studied whether or not adaptive IHb color enhancement would be of great help during ordinary endoscopy for determining the extent of invasion in cases of early gastric cancer. This technique was useful in the diagnosis of the extent of cancer invasion of depressed-type early gastric cancers. It is therefore expected that adaptive IHb color enhancement will be useful for detecting discolored areas especially in the corpus and for the qualitative diagnosis of cancer.

　The narrow band imaging (NBI) system is composed of a sequential electronic endoscope system and a source of light equipped with new narrow band filters corresponding to red, green and blue. This system with a magnifying endoscope was able to yield very clear images of the capillaries on the mucosal surface. When conventional magnifying endoscopic images and NBI images of type IIc early gastric cancer were compared, it was found that the capillary network in the depressed surface was more clearly visualized with the NBI system. Depressed differentiated-type adenocarcinomas are more likely to show fine network patterns, whereas undifferentiated-type adenocarcinomas are more likely to show irregular corkscrew patterns. These patterns, probably representing microvascular structure of the mucosal surface, would be specific for each histological type of carcinoma. CD31 and CD34 are known to be specific for the vascular endothelium. Three-dimensional images of micro-vessels with a laser scanning microscope from obtained-specimens are in the process of being compared with endoscopic images, with the goal of establishing a new diagnostic strategy based on microvascular pattern analysis. We have been using the NBI system for differential diagnosis between minute cancer and erosion, the degree of differentiation, and the extent of invasion of early gastric cancer.