Unexpected major venous injury in the setting of percutaneous arterial access for GORE TAG Thoracic Branch Endoprosthesis.

Inferior vena cava (IVC) injury during thoracic endovascular aortic repair is exceedingly rare. We present the case of an 80-year-old woman who developed a fatal IVC perforation at the iliac confluence during large-bore (24F) sheath insertion for thoracic endovascular aortic repair. Despite successful thoracic endograft deployment, the patient developed acute hypotension and hemorrhagic shock. Emergent exploratory laparotomy revealed hemoperitoneum from an IVC tear, likely caused by shearing forces transmitted through heavily calcified iliac arteries. This case highlights the importance of preoperative access planning in patients with small, calcified iliac vessels and maintaining a low threshold for suspecting retroperitoneal venous injury when clinical findings differ from angiography results.