Gastric wall structure using a 30 MHz endoscopic ultrasound probe, focusing upon delineation of the muscularis mucosae

Background: The normal gastric wall has been reported to appear to be a five-layered structure. The structure of the gastric wall using a 30MHz endoscopic ultrasound probe and especially the identification of the muscularis mucosae (MM), has not been analyzed clearly. Methods: In a basic study, 11 sections of normal gastric wall with 26 horizontally inserted nylon sutures were immersed in water. The sections were scanned and the findings correlated using standard histology. In a clinical study, 15 early gastric cancers were examined by a 30 MHz endoscopic ultrasound probe. Results: In a basic study, layers deeper than the lower part of the submucosa could not be seen using ultrasonography. The first to fourth layers represented the mucosal layer except the MM, the fifth layer (high-echo layer) represented the boundary echo and a part of the MM, while the sixth layer (low-echo layer) represented the rest of the MM. The muscularis mucosae was seen clearly in all samples. In a clinical study the layers deeper than the submucosal layer could not be seen and the MM was visible in 87% of cases. The depth of invasion was estimated accurately in 90% of mucosal cancers and in 80% of submucosal cancers. Conclusion: A 30MHz endoscopic ultrasound probe, which cannot image the entire gastric wall, can visualize the MM and may help to confirm the structure of gastric wall layers and improve the ability to determine the depth of invasion in gastric cancer.