Perforated ascending colonic mucinous adenocarcinoma with a subserosal mucin pool presenting as a giant cystic lesion: a case report.

Introduction and importance: Mucinous adenocarcinoma (MAC) represents 10-20% of colorectal cancers and is characterized by abundant extracellular mucin pools. We report an unusual case of ascending colonic MAC with a giant subserosal mucin pool presenting as a cystic lesion, complicated by perforation during bowel preparation. Case presentation: An 83-year-old woman presented with a 14-cm cystic mass in the ascending colon on computed tomography (CT). Approximately 2 hours after starting polyethylene glycol ingestion for colonoscopy, she developed acute abdominal pain. CT revealed pneumoperitoneum, prompting emergency laparotomy. Intraoperatively, an ascending colonic tumor with an attached 150 × 140 mm cystic lesion containing approximately 1 L of mucin was identified, with a 2-mm perforation in the non-tumorous bowel wall proximal to the tumor. Ileocecal resection with oncologic lymph node dissection and end ileostomy was performed. Histopathology revealed a well-differentiated adenocarcinoma with mucinous components (pT4aN1bM0, Stage IIIC). After completing adjuvant chemotherapy, the patient remains disease-free 2 years after surgery. Clinical discussion: The perforation was likely caused by an acute increase in intraluminal pressure due to bowel preparation, combined with functional luminal narrowing resulting from extrinsic compression by the giant cystic lesion. Because the perforation occurred proximal to the tumor rather than through the tumor itself, intraperitoneal tumor-cell or mucin spillage may have been minimal. Conclusion: MAC with a giant cystic lesion is rare and may predispose patients to perforation during bowel preparation. Careful bowel preparation, close symptom monitoring, and prompt evaluation with timely surgical management are important to avoid life-threatening complications.