In summary, although similar imaging techniques are used for the localization of
insulin and
gastrin secreting
islet cell tumors, the success rates are very different. Fortunately, the best results are obtained in the
tumor for which effective medical treatment is less available, namely
insulinomas, which can be found and successfully resected in over 90 per cent of patients. Both portal venous sampling and experienced intraoperative ultrasound are critical for successful surgery of small
insulin-secreting
tumors. Facilities without these resources should not explore patients when the conventional imaging studies are negative.
Gastrinomas, on the other hand, will elude detection by even the most experienced surgeons in over 20 per cent of patients with sporadic
Zollinger-Ellison syndrome in spite of positive portal venous sampling and intra-arterial
secretin studies. The very small size of these
tumors and their occurrence in more difficult to explore extrapancreatic sites provides the basis for this difference. However, patients with negative imaging studies and negative surgical explorations have an excellent prognosis on long-term follow-up when gastric acid hypersecretion is controlled. An annual computed tomographic scan is recommended since the appearance of a
tumor would mandate surgical resection because of the significant incidence of
malignancy in larger
tumors. However, progression to imageable
tumors has been unusual in our experience with this group of patients. There remains a small group of patients with highly malignant, rapidly metastasizing,
gastrin-secreting
islet cell carcinomas for whom localization is simple but of little relevance. However, locally invasive
gastrinomas may often be resectable and provide prolonged remission and even cure. Aggressive surgery, supported by detailed cross-sectional and angiographic localization, has a role in this small group of patients.