Pitfalls in endosonographic imaging of suspected insulinomas: pancreatic nodules of unknown dignity.

OBJECTIVE: Endosonography enables localization and characterization of gastroenteropancreatic neuroendocrine tumors. We have studied the problem of misleading abnormalities of pancreatic morphology as obtained by endosonographic imaging. DESIGN AND METHODS: A total of 438 endosonographies performed for known or suspected diseases of the adrenal glands and/or the pancreas and/or suspected metastases in the neighboring tissues were analyzed.
RESULTS: In the pancreas, nine benign insulinomas, four non-metastatic islet cell carcinomas, and multiple benign neuroendocrine tumors in one patient with multiple-endocrine neoplasia-1 (MEN-1) disease were detected and correctly localized as proven by postoperative histology. In three further patients with genetic diagnosis of MEN-1, asymptomatic tumors were detected and are under observation. However, we also found an 8 x 4 mm hypoechoic tumor in the cauda pancreatis of a patient with severe factitial hypoglycemia (glimepiride). In another patient suffering from severe hypoglycemia, a hypoechoic area of 24 x 10 mm in the processus uncinatus/caput pancreatis was found. Although organic hyperinsulinism was excluded, this patient underwent surgery because of suspected pancreatic carcinoma. There was normal pancreatic tissue in the abnormal region, which was also localized by intraoperative sonography. In a third patient with an adrenal carcinoma, a 6 x 3 mm hypoechoic nodule in the cauda pancreatis did not change its morphology over an observation period of 13 months, its clinical relevance is completely unclear.
CONCLUSIONS: Pancreatic nodules of unknown dignity were detected in nearly 1% of our patients and must be considered to be a diagnostic problem. These experiences clearly show, on the one hand, that pancreatic endosonography is a very useful diagnostic support in the management of endocrine tumor patients. However, on the other hand, endosonography of endocrine organs is not a substitute for careful endocrinological examination and testing and must be considered in the context of endocrinological findings.