Endosonography of insulin-secreting and clinically non-functioning neuroendocrine tumors of the pancreas: Criteria for benignancy and malignancy

Objective: Endosonography is a powerful tool in the diagnosis of gastroente ropancreatic neuroendocrine tumors. This study was performed in order to ch aracterize endosonographic criteria of malignant and benign neuroendocrine pancreatic tumors focussing on those typically presented to endocrinologist s, i.e. insulin-secreting tumors and clinically non-functioning tumors in M EN-1. Design: We studied six benign insulinomas, four hormone inactive benign neu roendocrine adenomas in MEN-1, and three non-metastatic neuroendocrine carc inomas with clinically symptomatic insulin secretion. Methods: Endosonography was performed using Pentax FG 32 UA endosonoscope w ith a longitudinal 7.5 MHz sector array. Results: Tumor diameter was larger in malignant tumors (19 - 70 / 47.0 +/- 25.9 mm) than in benign lesions (2.3 - 19 / 9.7 +/- 5.8 mm). Hypoechoic ech ogeneity was more or less resent in benign and in malignant tumors and coul d not be used as a criteria or differential diagnosis. Heterogenous or mult inodular structure on endosonographic imaging however, was an exclusive fea ture of malignant tumors. Echo-free areas representing cystic transformatio n or necrosis and vascular invasion were additional signs of malignancy. Conclusions: Molecular genetic diagnosis of MEN-1 and new therapeutic devel opments such as endoscopic surgery make sufficient imaging procedures in th e management of neuroendocrine pancreatic tumors mandatory. Besides valid d etection and exact localization, endosonography provides criteria for benig n and malignant tumors and thus may be helpful in planning therapeutic stra tegies.