Process of healing of mucosal defects in the esophagus after endoscopic mucosal resection: histological evaluation in a dog model. 
Resection of a large amount of the esophageal mucosa often causes esophageal ulcer and postoperative stricture.  The aim of this study was to evaluate the process of healing of defects in the esophageal mucosa after endoscopic mucosal resection (EMR).  Cap-assisted EMR was performed in the thoracic esophagus of six beagle dogs to prepare mucosal defects with a diameter ranging from 15 to 18 mm.  The process of mucosal healing was assessed histologically immediately after EMR, and on postoperative day (POD) 2, 4, 7, 14, and 28.  Immediately after EMR, a thin layer of the submucosa remained in the mucosal defect, and no damage to the muscularis propria was evident.  Ulcer formation and inflammatory cell invasion were observed in the remaining submucosa on POD 2 and 4.  Angiogenesis and collagen fiber hyperplasia were observed after POD 7.  Complete epithelialization of the ulcer was observed on POD 28.  In the muscularis propria, further destruction and atrophy were evident after POD 7.  Fibrosis of the muscularis propria was observed on POD 28.  In the esophageal wall after epithelial loss resulting from EMR, atrophy and fibrosis of the muscularis propria remain even after epithelialization.