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Insulinoma

German: Insulinom

1 Definition

An insulinoma is a rare insulin-producing tumor of the pancreas.

ICD-10 code: D13.7 and C25.4

2 Pathogenesis

Insulinomas usually develop from degenerated B cells of the pancreas that form an adenoma. In about half the cases, the adenoma also produces other gastrointestinal hormones, e.g. vasoactive intestinal polypeptide (VIP). In most cases (90%) there is only a singular insulinoma, whereas multiple microadenomas are less frequent. Only about 10% of insulinomas are malign. Insulinomas can appear in connection with multiple endocrine neoplasia (MEN).

3 Epidemiology

Insulinoma overall is a rare condition, although it is the most frequent endocrine tumor of the pancreas. Women are affected about twice as often as men.

4 Clinical relevance

Insulinomas are characterized by recurring hypoglycemia with blood sugar levels below 50 mg/dl. They produce the typical symptoms of low blood glucose levels:

The typical symptoms correspond to the so-called Whipple triad.

Further possible symptoms can be found in the article hypoglycemia. If the condition remains untreated for a long time, a significant increase in weight can be observed (anabolic effect of insulin).

5 Diagnosis

Clinical symptoms play a crucial role in diagnosing this condition. In cases of suspected insulinomas, a fasting test can be carried out. For this test, the patient stops eating for three days until symptomatic hypoglycemia occurs. Blood sugar, insulin and c-peptide levels are taken in regular intervals.

If an insulinoma is present, blood sugar levels drop comparatively fast and the glucose to insulin ratio increases, whereas this ratio decreases in healthy individuals. Patients with insulinoma also show increased c-peptide and proinsulin levels.

Insulin release of a diagnosed insulinoma can be inhibited by giving octreotide. About half of all insulinomas are granular and react to octreotide, whereas the other, agranular insulinomas cannot be inhibited.

5.1 Differential diagnosis

Other causes of hypoglycemia have to be excluded, for example hypoglycemia factitia due to the injection of insulin.

5.2 Localization diagnostics

Before therapy the insulinoma has to be located. Insulinomas in the centimeter range can easily be located using imaging techniques. Very small, multiple adenomas on the other hand sometimes cannot be located this way. Generally, the following imaging techniques can be used:

  • MRI (magnetic resonance angiography (MRA) and magnetic resonance cholangiopancreatography (MRCP))
  • CT scan of the abdominal region
  • Octreotide scan

The best suited imaging technique is the MRI scan because it provides very detailed data of the topographical situation in the prospect of surgical intervention.

If imaging techniques cannot successfully locate the insulinoma, the portal vein can be catheterized percutaneously or intraoperatively in order to selectively determine insulin concentrations.

6 Therapy

The treatment of choice is the complete surgical resection of the insulinoma. Before and during surgery, octreotide can be supplied to inhibit insulin release.

Pathological findings showing malignity of the tumor or metastases indicate interdisciplinary intervention consisting of precise surgery, chemotherapy, possibly in conjunction with radiation therapy.

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