An evaluation of anti-insulin radioimmunodetection in patients with suspected insulinoma

Nine patients with suspected insulinoma were scanned with iodine-131 labelled anti-insulin. The clinical diagnosis was subsequently confirmed at laparotomy in eight patients, two of whom had liver metastases. The primary insulinoma was accurately localized by anti-insulin scanning in four patients and these tumours ranged from 1 to 3 cm in diameter. Both computerized axial tomography (CT) scanning and pancreatic angiography had given false negative results in one of these patients. Hepatic metastases were correctly identified in one of two patients. No hepatic false positive reports occurred. Positive scan areas were graded as definite, probable or possible. All four of the pancreatic positive results graded as definite or probable positive were correct. Three false positive results occurred in the region of the pancreatic body, all had been graded as possible. Anti-insulin scanning failed to detect four subsequently proven insulinomata (3 mm-2 cm in diameter). Pelvic uptake of anti-insulin occurred in a patient who was found to have a para-ovarian tumour. An homogenate of this tumour also reacted with anti-insulin in a radioimmunoassay. A true negative pancreatic scan was obtained in this patient. We conclude that this technique is insufficiently accurate for routine clinical use.