Adult Pan-Colonic Intussusception Secondary to Poorly Differentiated Cecal Adenocarcinoma: A Rare Presentation of Stage IIA Colon Cancer.

Adult intussusception is rare, typically associated with an underlying pathology, and often presents with nonspecific symptoms. We report the case of a 68-year-old man presenting with diarrhea, abdominal pain, and weight loss. CT suggested volvulus versus intussusception, and emergent laparotomy revealed massive pan-colonic intussusception extending from the small bowel into the right colon and continuing through the transverse and descending colon to the sigmoid. A subtotal colectomy with end ileostomy was performed. The postoperative course was complicated by high serous drain output and transient hyponatremia, both managed conservatively. Pathology demonstrated a poorly differentiated cecal adenocarcinoma with weak neuroendocrine differentiation, staged pT3N0M0 (Stage IIA, American Joint Committee on Cancer 8th edition) with intact mismatch repair proteins. Oncology consultation identified high-risk features, and management options included adjuvant chemotherapy versus close observation with circulating tumor DNA and molecular profiling. This case depicts the rarity of adult pan-colonic intussusception, the need for oncologic resection given malignant lead points, and the importance of integrating molecular diagnostics into modern postoperative management.