Aneurysms and pseudoaneurysms of the superior mesenteric artery are potentially lethal and should be treated as urgently as possible. In a 52-year-old man with occasional epigastric pain, we accidentally discovered a superior mesenteric artery aneurysm that was ruptured with spontaneous tamponade in the uncinate process and in the head of the pancreas. The ruptured aneurysm had a heterogeneous appearance due to its thrombotic and hemorrhagic content, and it simulated a voluminous mass in the head and uncinate process of the pancreas, associated with mild dilatation of the main pancreatic duct. Recent advances in multidetector computed tomography and magnetic resonance imaging have enabled radiologists to develop a correct diagnosis of mesenteric aneurysms and pseudoaneurysms of the visceral branches of the abdominal aorta, and to differentiate this diagnosis from that of pancreatic or peripancreatic masses; angiography is currently used to confirm a diagnosis and to develop therapeutic treatments.