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Figure 6-1 A, Computed tomography scan in a 37-year-old man with a malignant nonfunctional neuroendocrine tumor arising in the neck of the pancreas. This patient presented with epigastric pain, weight loss, and bleeding varices. B, Subtraction angiogram showing a nonfilling segment of the superior mesenteric and portal veins (arrows). Note the large venous collaterals for the superior mesenteric vein to the distal portal vein in a 37-year-old man with multiple endocrine neoplasia type 1. C, Distal pancreatectomy specimen from a 37-year-old man with a tumor invading the superior mesenteric and proximal portal veins. A graft was used to replace the invaded vein segment.

If the value is more than 50, then organic hyperinsulinism is certain. Measurements of proinsulin and C-peptide have also been valuable in patients suspected of having organic hypoglycemia. The proinsulin accounts normally for less than 22% of the insulin immunoreactivity but for greater than 24% in more than 90% of patients with insulinomas. Furthermore, when the proinsulin level is greater than 40%, a malignant islet cell tumor should be strongly suspected. The C-peptide level is useful in ruling out factitious hypoglycemia caused by self-administration of insulin. Commercial insulin preparations contain no C-peptide, and low levels of this peptide, combined with high insulin levels, confirm the diagnosis of self-administration of insulin. Various insulin stimulation and suppression tests were once used when precise and accurate insulin measurements were not available. All these tests are currently considered obsolete. We have, however, introduced the insulin response to secretin stimulation as a valuable measure to differentiate multiple adenomas from nesidioblastosis and single adenoma. Patients with single adenomas do not respond to secretin, whereas patients with multiple adenomas and hyperplasia have excessive insulin response to the administration of secretin.

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