A Malignant Masquerade: Angiosarcoma Presenting as an Impending Rupture of an Abdominal Aortic Aneurysm.

Primary tumors arising from within the arterial wall are extremely uncommon and often present at advanced stages, making timely intervention challenging. Surgeons need to be aware of these rare conditions, as early detection and treatment can significantly improve patient outcomes. Angiosarcoma of the abdominal aorta is a particularly rare and aggressive malignancy, often resembling an aneurysm at risk of rupture. A 59-year-old woman presented with sudden onset of severe abdominal pain and was diagnosed with a 42 mm saccular abdominal aortic aneurysm, which was urgently repaired under the presumption of impending rupture. Intraoperatively, we found the aneurysm to be notably more fragile than a typical abdominal aortic aneurysm, while the rest of the aorta appeared healthy. This discrepancy raised suspicion of an atypical lesion, prompting us to resect the aneurysm and submit it for pathology. Subsequent immunohistochemical staining confirmed angiosarcoma, enabling timely referral for oncological management. Angiosarcoma is often difficult to diagnose based on computed tomography findings alone, so any atypical appearance of the aorta should raise suspicion of this malignancy, even in emergent surgery. This case shows the important role of careful intraoperative assessment and pathological examination in guiding definitive management.