BackgroundThere are few reports describing the unusual origin of the inferior mesenteric artery (IMA). We report a rare case of advanced sigmoid colon cancer with the IMA arising from the superior mesenteric artery.Case presentationA 59-year-old man with diarrhea and abdominal distention was diagnosed with advanced sigmoid colon cancer. Colonoscopy revealed a semi-circumferential cancer lesion in the sigmoid colon. Enhanced CT scan and CT angiography showed that the IMA directly originated from the superior mesenteric artery at the level of the second lumbar vertebra. PET-CT suggested metastases in the para-intestinal lymph nodes and the liver, but not in the central lymph nodes along the IMA. Preoperative diagnosis was sigmoid colon cancer cT4aN2aM1a cStage IVA(UICC, 8th edition). We performed laparoscopic complete resection as the radical treatment of the primary region prior to resection of the liver metastases. Intraoperative findings showed that the IMA was running parallel to the abdominal aorta; meanwhile, the colonic autonomic nerve was supplied from the lumbar splanchnic nerve at the caudal side of the duodenum. Central lymph nodes around the colonic autonomic nerve were dissected en bloc with the regional lymph nodes. Pathological radical resection including the regional lymph nodes metastasis was achieved. Two months later, complete resection of the liver metastasis was performed. After the adjuvant chemotherapy, no recurrence was observed 1.5 years after the liver resection was performed.ConclusionsPreoperative confirmation of the anatomy helped us to safely complete radical surgery in a patient with unusual bifurcation of the IMA.