Esophageal submucosal bulge with ultrasound endoscopic diagnosis of smooth muscle tumor What are submucosal lesions (SMTs) of the GI tract? As the name implies, they are lesions originating from the layers below the mucosal layer of the GI tract. Since they all appear as elevated lesions with normal surface mucosa under endoscopy, ordinary endoscopic techniques are unable to determine the level of origin and nature of the lesions, and ultrasound endoscopy is required to make the diagnosis. Common submucosal lesions of the gastrointestinal tract include gastrointestinal mesenchymal tumors, smooth muscle tumors, carcinoid tumors, lipomas, ectopic pancreas, hemangioblastoma, etc. SMTs generally do not have special clinical symptoms, but they are frighteningly common, so they should be diagnosed early and removed early if necessary.