Synchronous Primary Adenocarcinomas of the Hepatic and Splenic Flexures Presenting as Acute Large Bowel Obstruction in a 38-Year-Old Man: A Case Report.

Synchronous primary colorectal cancers (CRCs) are uncommon and are more frequently identified in older patients or in association with hereditary cancer syndromes. Although the incidence of early-onset CRC (EOCRC) is increasing, synchronous primary tumors in young individuals without identifiable risk factors remain rare. Presentation as acute large bowel obstruction further complicates diagnosis because complete preoperative colonoscopic evaluation is often not feasible. We report the case of a 38-year-old man with no significant medical or family history who presented with a two-day history of worsening generalized abdominal pain, nausea, vomiting, and constipation. Computed tomography (CT) demonstrated partial large bowel obstruction at the hepatic flexure. A water-soluble contrast enema subsequently revealed two distinct apple-core lesions at the splenic and hepatic flexures. The patient underwent emergent exploratory laparotomy with subtotal colectomy and ileocolic anastomosis. Intraoperatively, a 3.5 cm obstructing mass at the splenic flexure and a 4.5 cm polypoid mass at the hepatic flexure were identified. Histopathologic examination confirmed moderately differentiated (grade 2) adenocarcinomas in both lesions with no lymphovascular or perineural invasion. Eighteen lymph nodes were examined, and all were negative for metastasis. Surgical margins were negative. Immunohistochemistry showed intact mismatch repair protein expression (microsatellite stable). Preoperative and postoperative carcinoembryonic antigen levels were normal. Both tumors were staged as pT3N0M0 (stage IIA). The postoperative course was complicated by small bowel obstruction that resolved with conservative management; the patient was discharged after a seven-day hospitalization and remained well at the three-month follow-up with planned surveillance. This case highlights the importance of considering synchronous colorectal malignancies even in younger patients without traditional risk factors. When a complete colonoscopic assessment is not possible due to obstruction, adjunctive imaging such as contrast enema and extended resection are essential for adequate oncologic management.