Electrolyte Depletion Syndrome due to a 28 cm Rectal Villous Tumor: Successful Endoscopic Resection of One of the Largest Tumors Reported to Date—A Case Report

Electrolyte depletion syndrome (EDS), also known as McKittrick-Wheelock syndrome, is a rare but life-threatening condition caused by secretory diarrhea from colorectal villous tumors, often accompanied by severe electrolyte imbalances and renal dysfunction. Large, circumferential tumors have traditionally been managed with surgical resection, frequently requiring stoma formation. Recently, endoscopic submucosal dissection (ESD) has emerged as a minimally invasive alternative, although its feasibility for large rectal tumors remains limited. We report a case of EDS caused by a giant circumferential rectal villous tumor measuring approximately 28 cm, successfully treated with ESD. A 58-year-old man presented with persistent diarrhea, electrolyte disturbances, and acute kidney injury. Imaging and endoscopy revealed a circumferential villous tumor extending from the anal verge to the rectosigmoid colon, diagnosed as a villous adenoma without malignancy on biopsy. After careful discussion between the departments of gastrointestinal surgery and gastroenterology, ESD under general anesthesia was selected to avoid colectomy and stoma creation. En bloc resection of a 280 × 240 mm tumor was achieved without major complications. Prophylactic steroid injection and systemic steroid administration prevented post-ESD stricture. Histopathology revealed adenocarcinoma with minimal submucosal invasion (800 µm), no lymphovascular invasion, and negative resection margins, indicating curative resection. At 6-month follow-up, no recurrence or stricture was observed. This case highlights the potential of ESD as a definitive and less invasive treatment option for EDS caused by large rectal villous tumors when performed with appropriate therapeutic planning and meticulous postoperative care.