A case of chronic contained rupture of abdominal aortic aneurysm mimicking a retroperitoneal tumor.

Chronic contained rupture of abdominal aortic aneurysm (CCR-AAA) is a rare subtype of abdominal aortic rupture that can mimic other retroperitoneal lesions. We report a case of CCR-AAA in a man in his sixties who presented with a 10-month history of right low back pain and weight loss. Contrast-enhanced computed tomography (CT) revealed a lobulated retroperitoneal mass around the abdominal aorta, initially misdiagnosed as a possible hemorrhagic retroperitoneal tumor. Despite multiple imaging studies including CT, magnetic resonance imaging (MRI), and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET)/CT, as well as a CT-guided biopsy, the correct diagnosis remained elusive for 34 months. Key findings included subtle aortic wall irregularity on CT, high signal intensity on T1-weighted MRI suggesting hematoma, peripheral FDG uptake on PET/CT, and histological findings of biopsy tissue consistent with organizing hematoma. Surgery confirmed the diagnosis, revealing an organized hematoma with a defect in the right wall of the abdominal aortic aneurysm. This case demonstrates that CCR-AAA can present with atypical radiological features, potentially leading to misdiagnosis. When encountering a para-aortic mass with a hemorrhagic component, careful observation of the AAA morphology and aortic wall contour is crucial for an accurate diagnosis of CCR-AAA.