Imaging description

Pancreatic neuroendocrine tumors (PNETs) have variable CT appearances, but demonstrate a distinctive CT appearance when they present as small, hypervascular masses within the pancreatic parenchyma. Unlike adenocarcinoma, which is typically hypovascular and most conspicuous on the venous phase, hypervascular PNETs are typically more vascular than the pancreatic parenchyma on the arterial and/or venous phase(s). This appearance can be mimicked by a splenic artery aneurysm that is partially or completely surrounded by pancreatic parenchyma (Figure 76.1). The distinction is made by demonstrating contiguity with the splenic artery on arterial-phase imaging, facilitated by use of 2D multiplanar reconstructions and 3D rendering.

Importance

Distinction of a splenic artery aneurysm from a pancreatic neuroendocrine tumor is essential, for several reasons. Biopsy of a splenic artery aneurysm mistaken for a PNET could result in catastrophic hemorrhage. Resection based on a presumptive CT or MR diagnosis would subject the patient to an unnecessary surgical procedure with significant morbidity rates.

Typical clinical scenario

Splenic artery aneurysms are estimated to occur in 0.1 to 10.4% of the general population. Splenic artery aneurysms have a strong female predominance, with a female to male ratio of 4:1. Splenic artery aneurysms are defined by diameter greater than 1 cm. Splenic artery aneurysms may be mistaken for pancreatic neuroendocrine tumors when proper CT technique is not performed, including high spatial resolution, arterial and venous phase acquisitions, as well as 2D multiplanar reconstructions and 3D rendering. A single venous phase acquisition without narrow reconstruction sections can make the distinction of the two entities challenging.

Differential diagnosis

Differential diagnosis for a vascular lesion in the pancreas includes metastasis from renal cell carcinoma, gastrointestinal stromal tumor, peripancreatic paraganglioma, and intrapancreatic splenule. The presence of calcification would be more common with either a PNET or a splenic artery aneurysm.