Incidental nonfunctioning pancreatic neuroendocrine tumors: Contrast enhanced ultrasound features in diagnosis1

Preoperative suspicion of malignancy in nonfunctioning pancreatic neuroendocrine tumors (pNETs) is mostly based on tumor size. We retrospectively analyzed the contrast enhanced ultrasound (CEUS) features of a series of histopathologically proved nonfunctioning pNETs.

In this retrospective study, 37 surgery and histologically proved nonfunctioning pNETs were included. All pNETs lesions were incidentally detected by transabdominal ultrasound. B mode ultrasound (BMUS) and CEUS features were reviewed and analyzed. 52 histopathologically proved pancreatic ductal adenocarcinoma (PDACs) lesions were included as a control group.

All nonfunctioning pNETs patients showed no typical clinical symptoms. No significant differences were observed in size, echogenicity or internal color flow imaging signal between pNETs and PDAC patients (P > 0.05). Most of nonfunctioning pNETs showed a well-defined tumor margin. The presence of pancreatic duct dilatation was less frequently observed in nonfunctioning pNETs patients (P < 0.05). After injection of ultrasound contrast agents, homogeneous enhancement was more commonly observed in nonfunctioning pNETs group (P < 0.05). During arterial phase of CEUS, most of nonfunctioning pNETs were hyper- or isoenhanced (32/37, 86.5%), whereas most of PDACs were hypoenhanced (34/52, 65.4%) (P < 0.05). Nonenhanced necrosis area was more commonly detected in PDACs (P = 0.012).

CEUS features are helpful for preoperative non-invasive differential diagnosis of nonfunctioning pNETs, assisting further clinical decision-making process.