Endoscopic full-thickness resection of a lateral spreading rectal tumor after unplanned injection of dilute hyaluronic acid into the subserosal layer (with video).

A 74-year-old woman underwent colonoscopy for investigation of a liver tumor. A lateral spreading tumor of the non-granular type (LST-NG), 25 mm in diameter, was detected at the rectosigmoid junction. As magnifying image-enhanced colonoscopy suggested a tubulovillous adenoma, endoscopic mucosal resection (EMR) was chosen for removal of the LST-NG. The lesion was effectively and evenly lifted after injection of 0.4% hyaluronic acid diluted with glycerol in the ratio of 1:1. A small amount of indigo-carmine dye was also added for coloration of the plane of resection. The lesion was completely removed en bloc. Although a blue-colored layer was identified in the resection defect, a small amount of a whitish layer was detected above the blue layer. The muscle layer was clearly located on the underside of the resected polyp. A total of 14 endoclips were used to close the defect completely. The patient was successfully treated conservatively without surgery. Histology of the resected specimen showed that it contained a tubulovillous adenoma with the submucosal layer and both layers of the muscularis propria. The surgical margin was free of neoplastic change horizontally and vertically. To the best of our knowledge, this is the first case report of full-thickness resection associated with EMR after unplanned injection of dilute hyaluronic acid into the subserosal layer rather than the intended submucosal layer. We describe how to promptly recognize this complication during colonoscopy, in order to achieve immediate closure of the defect, with the identification of a "mirror target sign" on the colonic wall.