Insulinoma

• • Hypoglycemic symptoms produced by fasting

  • Blood glucose below 50 mg/dL during symptomatic episodes

  • Relief of symptoms by IV administration of glucose

Epidemiology

• • Insulinomas have been reported in all age groups

  • 75% are solitary and benign

  • 10% are malignant; metastases are usually evident at the time of diagnosis

  • Most are sporadic, solitary, benign lesions < 2 cm, occurring in equal distribution throughout the pancreas

  • 15% are manifestations of multifocal pancreatic disease—either adenomatosis, nesidioblastosis, or islet cell hyperplasia

  • In patients with multiple endocrine neoplasia 1 (MEN 1), insulinomas are typically multifocal

Symptoms and Signs

• • Palpitations

  • Sweating

  • Tremulousness

  • Weight gain

  • Bizarre behavior

  • Memory lapse

  • Unconsciousness

Laboratory Findings

• • Fasting hypoglycemia in the presence of inappropriately high levels of insulin

  • -Ratio of plasma insulin:glucose > 0.3 is diagnostic

  • Proinsulin levels > 40% suggest a malignant islet cell tumor

  • Elevated C-peptide levels exclude self-administration of insulin

  • Absent urine sulfonylurea levels exclude oral hypoglycemics

Imaging Findings

• • High-resolution CT and MRI scans demonstrate about 40% of tumors

  • Endoscopic US exam of the pancreas successfully identifies 80-95% of tumors preoperatively

  • Intraoperative US can identify a pancreatic tumor in nearly all cases and is the gold standard

  • More invasive techniques, such as transhepatic portal venous sampling and arteriography with selective calcium infusion are best used for reexploration after unsuccessful intraoperative localization

• • After diagnosis has been made by demonstration of fasting hypoglycemia and elevated insulin levels, the next step is localization of the insulinoma

  • Attempts at preoperative localization should be limited to noninvasive techniques (CT scan or MRI and endoscopic US)

Rule Out

• • Non-islet cell tumors associated with hypoglycemia (hemangiopericytoma, fibrosarcoma, leiomyosarcoma, hepatoma, adrenocortical carcinoma)

  • Surreptitious self-administration of insulin

  • -Circulating C peptide levels are normal in these patients but elevated in most patients with insulinoma

  • Non-insulinoma pancreatogenous hypoglycemia syndrome

  • -Postprandial hypoglycemia with hyperinsulinism

    -Frequently post-gastric bypass procedure for morbid obesity

    -Calcium angiogram stimulates rise in hepatic vein insulin levels from all areas of the pancreas

• • Fasting determination of blood glucose and insulin levels; hypoglycemia with elevated insulin level

  • Preoperative localization

  • -CT scan or MRI

    -Endoscopic US

  • Control of hypoglycemia

  • Intraoperative US

When to Admit

• • Severe, symptomatic hypoglycemia

• • The tumor may be enucleated if it is superficial, or resected as part of a partial pancreatectomy if it is deep-seated

  • Resection of metastatic lesions is warranted if technically feasible

Surgery

Indications

• • All patients with technically resectible lesions

Medications

• • Diazoxide or octreotide to suppress insulin release

  • Streptozocin is ...