Endoscopic ultrasound imaging of the gastrointestinal tract wall. White arrows point to the corresponding histologic structures and echogenicity: 1) superficial mucosa (hyperechoic); 2) deep mucosa (hypoechoic); 3) submucosa (hyperechoic); 4) muscularis propria (hypoechoic); 5) serosa and subserosal fat (hyperechoic). (a) Subepithelial tumor continuous with the muscularis propria layer.