Imaging description

Pseudoaneurysm, also known as a false aneurysm, is a collection of flowing blood that is encapsulated and communicates with the ruptured arterial lumen contained only by the adventitia or surrounding soft tissue. After contrast administration, the sac may fill with contrast material if it is not completely thrombosed and the enhancement follows that of the feeding artery (Figures 75.1 and 75.2). Thrombus within the sac may appear as high-attenuation filling defect on unenhanced CT or as high-signal-intensity defect on fat-suppressed T1-weighted MR images. Diagnostic specificity may be improved with 3D multidetector CT angiography (Figure 75.3). Three- dimensional renderings are valuable for distinction from tortuous vessel or small, hyperattenuating islet cell tumor of the pancreas. Conventional angiography remains the standard of reference and provides the capability of endovascular management (Figure 75.4).

Importance

Pseudoaneurysms complicate 10% of cases of acute pancreatitis, most commonly affecting the splenic artery, although the hepatic, gastric, gastroduodenal, and pancreaticoduodenal arteries may also be involved due to erosion by pancreatic enzymes. Early detection and management are paramount given the high mortality associated with rupture, which may be up to 90% if bleeding is left untreated. Rupture can occur into the peritoneum, adjacent hollow organs, pseudocyst or pancreatic duct. Given enhancement characteristics, there is risk of mistaking pseudoaneurysms for a hypervascular pancreatic mass such as neuroendocrine tumor. Misdiagnosis leading to biopsy may have catastrophic consequences due to severe bleeding.

Typical clinical scenario

Pseudoaneurysm may be asymptomatic and could be detected incidentally during imaging patients with complicated pancreatitis and may be mistaken for a mass at routine imaging, especially if the lumen is completely thrombosed and fails to enhance on CT. In case of hyperenhancement, it may also be mistaken for a hypervascular lesion such as a neuroendocrine tumor.