Insulinoma

Written by Colleen Story | Published on July 15, 2012
Medically Reviewed by Peter Rudd, MD

What Is an Insulinoma?

An insulinoma is a rare type of small pancreatic tumor. It produces an excess of the hormone insulin. About 90 percent of the time, the tumor is benign (non-cancerous).

Because the tumor produces excess insulin, it can lead to low blood sugar. Low blood sugar is also known as hypoglycemia. It can cause serious symptoms, such as:

  • confusion or forgetfulness
  • blurred vision
  • lightheadedness
  • unconsciousness

Most of the time, this tumor needs to be surgically removed.

What Causes Insulinoma?

Scientists don’t know why people get insulinomas. The tumors typically show up without any warning.

When a person eats, the pancreas creates insulin. The insulin helps use and store the sugar energy (glucose) from your food. Once the glucose has been absorbed, the pancreas cuts back on insulin. This feedback loop keeps blood sugar levels stable.

Glucose regulation changes when someone has an insulinoma. The tumor continues to produce insulin even when blood sugar drops. This can lead to hypoglycemia.

Symptoms of hypoglycemia range from mild to more serious. They depend on how much insulin the tumor is producing and how low the blood glucose falls. Symptoms typically become more problematic with time.

Who Is at Risk?

Insulinomas are rare. According to an article in Hepatobiliary & Pancreatic Diseases International (Dennis Vaidakis, et al., 2010), they affect fewer than five out of one million people each year. The tumors are slightly more common in women. The median age at diagnosis is 47 years.

Most tumors are small, measuring less than two centimeters (less than one inch). Only about 10 percent of these tumors are malignant (cancerous). Cancerous tumors tend to occur more often in people who have MEN-1 syndrome. This is an inherited disease that causes enlargement of one or more hormonal glands. Risk also seems to be higher for those with von Hippel-Landau syndrome. This inherited condition causes abnormal blood vessel growth.

Most tumors are solitary, occurring only one at a time. In about 10 percent of cases, patients have multiple tumors.

What Are the Symptoms?

People with insulinoma don’t always have noticeable symptoms. Mild low blood sugar symptoms are often ignored or mistaken for other problems. People may go for several decades without a diagnosis.

More severe symptoms of insulinoma can affect the brain. They can also affect the adrenal glands. These glands regulate stress response and heart rate.

Sometimes symptoms seem similar to those of epilepsy. Epilepsy is a neurological disorder that causes seizures.

Mild symptoms include:

  • double vision or blurred vision
  • confusion
  • anxiety
  • dizziness
  • abnormal behavior
  • weakness
  • sweating
  • hunger
  • tremors
  • weight gain

Symptoms that are more serious may include:

  • convulsions/seizures
  • rapid heart rate or heart pounding
  • amnesia
  • loss of consciousness or coma

Sometimes tumors grow large, or spread to other body parts. Symptoms in these cases may include:

  • abdominal pain
  • back pain
  • diarrhea
  • jaundice (yellowing of the skin and eyes)

How Is Insulinoma Diagnosed?

You will likely be given a blood test to check your glucose and insulin levels if you have signs of hypoglycemia. A low blood glucose paired with a high insulin level is a sign of insulinoma.

The lab may also check for:

  • proteins that block the production of insulin
  • drugs that cause the pancreas to release more insulin
  • other hormones that affect insulin production

If these tests come back positive, your doctor may order a 72-hour fast. This is considered the “gold standard” diagnosis of insulinoma. For this test:

  • You will be hospitalized.
  • You will be allowed to drink only calorie-free beverages.
  • Your blood glucose will be measured at least every six hours.

Additional tests may include a CT or MRI scan. These imaging tests help the doctor find the tumor. Alternatively, your doctor may use selective arterial calcium stimulation to check for abnormal insulin secretion from the pancreas.

An endoscopic ultrasound may be used if the tumor cannot be found with standard scans. This test uses sound waves to take images from inside the body. An ultrasound probe and biopsy needle are attached to an endoscope. This thin, flexible probe is easily threaded into your body. Then, if the tumor is located, the needle can be used to take a small biopsy. This can be used to determine whether the tumor is cancerous.

How Is Insulinoma Treated?

Standard treatment for insulinoma is tumor removal. A portion of the pancreas may be removed as well. This typically cures the disease.

There are various types of surgery for insulinoma. The number and location of tumors determine the surgery process.

If there is only one small pancreatic tumor, it will be removed laparoscopically. Laparoscopic surgery is minimally invasive surgery. Miniature instruments are used and only a small incision is made.

Larger or multiple tumors may require abdominal surgery. This is a more invasive surgery with a longer healing time.

When the tumors have spread, part of the pancreas may need to be removed. Sometimes part of the stomach or liver may be removed as well.

There are rare cases in which tumor removal is less effective. This is usually true only for malignant tumors. In these cases, doctors will prescribe medications to control blood sugar. Other treatments for malignant tumors include:

  • chemotherapy
  • radiofrequency ablation
  • cryotherapy

Ablation uses radio waves to kill cancer cells. Cryotherapy destroys cells by freezing.

What Is the Expected Outcome?

Surgery has an extremely high success rate. However, tumors can return. Recurrence is more common in patients who have multiple tumors.

A very small number of patients may develop diabetes after surgery.

Complications are more likely in patients with malignant tumors. This is particularly true when tumors have spread to other organs. These patients may need more follow-up care.

Can I Prevent Insulinoma?

The cause of insulinoma is unknown, so there is no known way to prevent it. However, you can reduce your risk of hypoglycemia by following a healthy diet and exercise regimen. In addition, keep your pancreas healthy with these tips:

  • Avoid smoking.
  • Eat less red meat.
  • Maintain a healthy weight.
  • Increase the amount of fruits and vegetables in your diet.
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