Rare Adult Ileo–Ileo–Colic Intussusception Caused by an Ileal Lipoma with Spontaneous Ileal Rupture and Rectal Hemorrhage: A Case Report with a Hypothesis-Generating Discussion of Mesenteric Anatomical Variability

Background and Clinical Significance: Adult intussusception is rare, accounting for approximately 5% of all intussusceptions and 1–5% of adult bowel obstructions, whereas the ileo–ileo–colic subtype is exceptionally uncommon. We report a rare case of ileo–ileo–colic intussusception caused by an ileal lipoma and complicated by spontaneous ileal rupture and rectal hemorrhage, emphasizing the diagnostic challenge and proposing the hypothesis that mesenteric anatomical variability may have contributed to its pathophysiology. Case Presentation: A 61-year-old man presented with progressive abdominal distension, right lower quadrant pain and mass, and signs of bowel obstruction. Contrast-enhanced abdominal CT showed an ileo–ileo–colic intussusception extending into the ascending colon, with a typical target sign and marked ischemic changes involving the ileal loops. Emergency laparotomy confirmed a complex ileo–ileo–colic intussusception extending into the right colon, with an ileal lipoma acting as the lead point. The intussuscepted bowel had undergone spontaneous rupture with active bleeding, explaining the rectal hemorrhage. The patient underwent right hemicolectomy with ileocecal resection and side-to-side ileocolic anastomosis. Histopathological examination confirmed a submucosal ileal lipoma associated with transmucosal ischemic necrosis. Recovery was uneventful, and no recurrence or late complications were observed at 6- and 12-month follow-up. Conclusions: This case highlights an exceptionally rare and severe presentation of adult intussusception. Early CT diagnosis and prompt surgical resection are essential when ischemia, necrosis, or failed reduction are present. Mesenteric anatomical variability is proposed as a plausible contributing factor to the extensive telescoping and vascular compromise observed in this patient, a hypothesis that warrants further anatomical investigation.