18FDG positron emission tomography imaging in gastrointestinal neuroendocrine tumours (GI-NET): preliminary report.

A correlation between the entity of 18FDG uptake and the malignancy rate has been reported in various types of neoplasms. In the present study we investigated this aspect in a group of 5 patients affected by GI-NET; 18FDG PET and conventional imaging (CI), i.e. US, CT and/or MRI, was performed in all the patients, and in 4 of them 111In-octeoride scan too. They were 4 M and 1 F, mean age 51 years: 1 had pancreatic somatostatinoma (2.5 cm diameter), 1 had pancreatic gastrinoma (1.5 cm diameter), 1 had both pancreatic and duodenal microgastrinomas (3 to 5 mm diameter), and 2 had agressive malignant pancreatic NET (3 and 1 cm diameter, respectively) the first one with liver metastases and the second one with both liver and regional lymphnode spread. Hystologic findings were obtained in all the cases. PET scan revealed a significant 18FDG uptake in the 2 cases with agressive malignant NET; in 1 of them PET was also the only technique capable to detect the spread to nodes and liver, whereas in the other case the liver metastases were identified only by CT scan. PET showed a faint, not significant pancreatic uptake in the patient with multiple microgastrinomas, while was negative in the patients with somatostatinoma and gastrinoma. CI visualized a pancreatic mass in all the cases; however in the patient with multiple microgastrinomas CT revealed a pancreatic mass that at surgery was demonstrated to be a necrotic area (false positive result). 111In-octeotride scan was positive in the patients with somatostatinoma and gastrinoma whereas no significant uptake was shown in the case of microgastrinomas and in 1 case of malignant NET. Conclusions: our preliminary results seem to suggest that a high 18FDG uptake appears to be correlated with a malignant biological behaviour of GI-NET. A greater number of cases is needed to confirm these promising data