Massive haematemesis as the first manifestation of superior mesenteric and portal vein thrombosis in a healthy young adult.

Superior mesenteric vein (SMV) and portal vein thrombosis are rare but serious causes of intestinal ischaemia, and haematemesis as an initial presentation is highly uncommon. We report the case of a 39-year-old previously healthy man who presented with acute haematemesis following diffuse abdominal pain. Contrast-enhanced computed tomography revealed complete thrombosis of the portal and SMV with ischaemic small bowel. Emergency laparotomy confirmed extensive jejunal and ileal gangrene, requiring near-total small-bowel resection with end jejunostomy. Postoperatively, the patient required intensive care with anticoagulation, parenteral nutrition, and broad-spectrum antimicrobials. His course was complicated by high jejunostomy output, catheter-related bloodstream infection, and bilateral pulmonary embolism despite anticoagulation. Thrombophilia testing revealed low Protein S levels. With continued supportive care, he gradually improved, his inflammatory markers normalized, and he was discharged haemodynamically stable with plans for long-term nutritional and anticoagulation support. This case illustrates a rare presentation of SMV and portal vein thrombosis, underscoring the importance of early diagnosis and intervention.