Insulinomas are rare type of functional neuroendocrine tumours with an incidence estimated at 1 to 4 new cases per million persons per year. They are called functional because they produce insulin and cause blood sugar levels, to drop.

Insulinoma is one of the most common types of tumour arising from the islets of Langerhans cells (pancreatic endocrine tumours).

Estimates of malignancy (metastases) range from 5% to 30%. Over 99% of insulinomas originate in the pancreas, with rare cases from ectopic pancreatic tissue.

 About 5% of cases are associated with tumours of the parathyroid glands and the pituitary (Multiple endocrine neoplasia type 1) and are more likely to be multiple and malignant. Most insulinomas are small, less than 2 cm.

 The most common symptoms of insulinomas are confusion, sweating, dizziness, weakness and relief with eating. These symptoms are caused by low blood sugar known as hypoglycemia.

There can often be a delay in the diagnosis due to the vague and varied symptoms that these tumours can cause.

Most insulinomas are solitary and benign and therefore surgical resection can often result in a cure, but there is a proportion of insulinomas that become malignant so it is vital that the correct diagnostic techniques are used.

The role of the pancreas

In a healthy person the pancreas produces both insulin and glucagon. When blood sugar rises after a meal, beta cells in the pancreas release insulin. This helps sugar from food to enter the blood cells and lowers levels of glucose to normal.

If blood sugar falls too low then alpha cells in the pancreas produce glucagons that triggers the liver to release glycogen. This is converted into blood glucose, thereby lifting levels of blood sugar to normal.

What is known about insulinomas?

In most cases a single tumor develops in the beta cells (the insulin producing cells) within the pancreas. In a very small number of cases (1-3%) the tumour will develop in insulin producing cells that have 'escaped' into the abdomen. The reason why tumours form is not yet fully understood. They may be present form many years prior to diagnosis as the symptoms they cause may be confused with other conditions.