This case report details a 74-year-old female patient who presented with imaging findings suggesting an intramural hematoma of the ascending aorta, but surgical exploration revealed periaortic lymphoma. Despite multiple imaging showing features typical of intramural hematoma, intraoperative findings confirmed a thick encasement by lymphoma without active disease. The report emphasizes the diagnostic challenges and the necessity for vigilant evaluation in similar cases due to the potential for serious outcomes if misdiagnosed.