A 42-year-old obese woman presented with severe postoperative sepsis and MODS ten days after sleeve gastrectomy. The condition was caused by a large dehiscence of the staple line beneath the GE junction. Despite multiple surgical revisions and negative-pressure wound therapy, she developed additional complications, including Aspergillus pneumonia and acute renal failure requiring hemodialysis. After three months of intensive care, follow-up imaging revealed a 12-cm retrogastric cavity containing purulence and necrotic tissue. Thirteen consecutive sessions of endoscopic vacuum therapy failed to achieve healing. We ultimately decided to perform endoscopic full-thickness gastric myotomy along the staple line to open and connect the cavity with gastric lumen. This intervention resulted in complete resolution of the cavity within five weeks.