Successful surgery for pancreatic neuro-endocrine tumours (NET) requires accurate tumour localisation. Interpretation of cross-sectional imaging is often difficult, particularly after pancreatic surgery. Imaging by somatostatin-receptor-scintigraphy with indium-labelled octreotide may be useful in identifying recurrent disease; however, octreotide scans may be negative in some pancreatic NET, due to a low level of expression of somatostatin receptors. The GLP-1 receptor is abundantly expressed in insulinomas and gastrinomas and offers an alternative target for peptide scintigraphy. Exendin-4 is a potent GLP1 agonist; indium-labelled DTPA-Exendin-4 has been proposed as a potential imaging ligand for pancreatic NET. We report our experience with these two receptor-scintigraphy imaging methods in two patients with different pancreatic manifestations of MEN1.
RW, age 69, known to have MEN1, developed symptomatic hypoglycaemia and was found to have an insulinoma with liver metastases. These lesions were resected but the following year his hypoglycaemia recurred and a CT scan revealed a 1.7 cm lymph node in the pancreatic bed. He was treated with lanreotide; 18 months later the node had increased to 4.3 cm. A gallium-octreotide PET scan was negative, but an 111In-DTPA-exendin-4 scan was intensively positive, revealing the extent of the tumour.
JB, age 59, was referred with a new diagnosis of diabetes. He had MEN1, and following an episode of spontaneous hypoglycaemia had had resection of multifocal pancreatic insulinoma 13 years earlier. He had recently developed a troublesome rash affecting his abdomen, genitals and limbs, associated with recurrent DVT. Glucagonoma was confirmed biochemically. CT scan showed no evidence of pancreatic tumour; an exendin-4 SPECT scan was negative, but an octreotide scan demonstrated tumour recurrence in the head of pancreas and an adjacent node.
These cases illustrate the different sensitivities of two receptor-scintigraphy imaging methods. GLP1 based imaging appears to be useful in insulinoma, but glucagonoma may be better imaged with octreotide.