Insulinoma: Causes, Symptoms, and Diagnosis
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Insulinoma

What Is an Insulinoma?

An insulinoma is a small tumor in the pancreas that produces an excess amount of insulin. In most cases, the tumor isn’t cancerous. Most insulinomas are less than 2 centimeters in diameter.

The pancreas is an endocrine organ located behind your stomach. One of its functions is to produce hormones that control the level of sugar in your bloodstream, such as insulin. Normally, the pancreas stops creating insulin when your blood sugar drops too low. This allows your blood sugar levels to return to normal. When an insulinoma forms in your pancreas, however, it will continue to produce insulin, even when your blood sugar is too low. This can lead to severe hypoglycemia, or low blood sugar. Hypoglycemia is a dangerous condition that can cause blurred vision, lightheadedness, and unconsciousness. It can also be life-threatening.

An insulinoma usually needs to be surgically removed. Once the tumor is removed, complete recovery is very likely.

What Are the Symptoms of an Insulinoma?

Symptoms

People with insulinomas don’t always have noticeable symptoms. When symptoms do occur, they can vary depending on the severity of the condition.

Mild symptoms include:

  • double vision or blurred vision
  • confusion
  • anxiety and irritability
  • dizziness
  • mood swings
  • weakness
  • sweating
  • hunger
  • tremors
  • sudden weight gain

More severe symptoms of insulinoma can affect the brain. They can also affect the adrenal glands, which regulate stress response and heart rate. Sometimes, symptoms seem similar to those of epilepsy, a neurological disorder that causes seizures. Symptoms that are seen in more serious cases of insulinoma may include:

  • convulsions or seizures
  • a rapid heart rate (greater than 95 beats per minute )
  • difficulty concentrating
  • loss of consciousness or coma

In some cases, insulinomas can get bigger and spread to other parts of the body. When this occurs, you can get the following symptoms:

  • abdominal pain
  • back pain
  • diarrhea
  • jaundice, or yellowing of the skin and eyes

What Causes an Insulinoma?

Causes

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

When you eat food, the pancreas creates insulin. Insulin is a hormone that helps your body store the sugar from your food. Once the sugar has been absorbed, the pancreas stops producing insulin. This process usually keeps blood sugar levels stable. However, it can be disrupted when an insulinoma develops. The tumor continues to produce insulin even when your blood sugar drops too low. This can lead to hypoglycemia, a serious condition characterized by low blood sugar levels.

Who Is at Risk for an Insulinoma?

Risk Factors

Insulinomas are rare. Most are small and measure less than 2 centimeters in diameter. Only 10 percent of these tumors are cancerous. Cancerous tumors tend to occur more often in people who have multiple endocrine neoplasia type 1. This is an inherited disease that causes tumors in one or more hormonal glands. The risk for insulinoma also seems to be higher for those with von Hippel-Lindau syndrome. This inherited condition causes tumors and cysts to form throughout the body.

Insulinomas also tend to affect women more than men. They most commonly develop in people who are between ages 40 and 60.

How Is an Insulinoma Diagnosed?

Diagnosis

Your doctor will perform a blood test to check your blood sugar and insulin levels. A low blood sugar level with a high insulin level indicates the presence of an insulinoma.

The test can also check for:

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

Your doctor may order a 72-hour fast if the blood test indicates that you have an insulinoma. You’ll stay in the hospital while you fast so your doctor can monitor your blood sugar levels. They’ll measure your blood sugar levels every six hours at least. You won’t be able to eat or drink anything except water during the fast. You’ll likely have very low blood sugar levels within 48 hours of starting the fast if you have an insulinoma.

Your doctor may perform more tests to confirm the diagnosis, including an MRI or CT scan. These imaging tests help your doctor determine the location and size of the insulinoma.

An endoscopic ultrasound may be used if the tumor can’t be found using a CT or MRI scan. During an endoscopic ultrasound, your doctor inserts a long, flexible tube into your mouth and down through the stomach and small intestine. The tube contains an ultrasound probe, which emits sounds waves that produce detailed images of your pancreas. Once the insulinoma is located, your doctor will take a small sample of tissue for analysis. This can be used to determine whether the tumor is cancerous.

How Is an Insulinoma Treated?

Treatment

The best treatment for an insulinoma is surgical removal of the tumor. A small part of the pancreas may also be removed if there’s more than one tumor. This typically cures the condition.

There are various types of surgery that can be performed to remove the insulinoma. The location and number of tumors determine which surgery will be used.

Laparoscopic surgery is the preferred option if there’s only one small pancreatic tumor. This is a low-risk, minimally invasive procedure. During laparoscopic surgery, your surgeon makes several small incisions in your abdomen and inserts a laparoscope through the incisions. A laparoscope is a long, thin tube with a high-intensity light and a high-resolution camera at the front. The camera will display the images on a screen, allowing the surgeon to see inside your abdomen and guide the instruments. When the insulinoma is found, it will be removed.

Part of the pancreas may need to be removed if there are multiple insulinomas. Sometimes, part of the stomach or liver may be removed as well.

In rare cases, removing the insulinoma won’t cure the condition. This is usually true when the tumors are cancerous. Treatments for cancerous insulinomas include:

  • radiofrequency ablation, which uses radio waves to kill cancerous cells in the body
  • cryotherapy, which involves the use of extreme cold to destroy cancerous cells
  • chemotherapy, which is an aggressive form of chemical drug therapy that helps destroy cancerous cells

Your doctor may also prescribe medications to control blood sugar levels if surgery wasn’t effective.

What Is the Long-Term Outlook for People with an Insulinoma?

Outlook

The long-term outlook for people with an insulinoma is very good if the tumor is removed. After surgery, most people recover completely without complications. However, an insulinoma may return in the future. Recurrence is more common in people who have multiple tumors.

A very small number of people may develop diabetes after surgery. This usually only occurs when the entire pancreas or a large portion of the pancreas is removed.

Complications are more likely in people with cancerous insulinomas. This is particularly true when the tumors have spread to other organs. The surgeon may not be able to remove all the tumors completely. In this case, more treatment and follow-up care will be necessary. Luckily, only a small number of insulinomas are cancerous.

How Can an Insulinoma Be Prevented?

Prevention

Doctors don’t know why insulinomas form, so there’s no known way to prevent them. However, you can reduce your risk of developing hypoglycemia by exercising regularly and maintaining a healthy diet. This diet should largely consist of fruits, vegetables, and lean protein. You can also keep your pancreas healthy by eating less red meat and quitting smoking if you smoke. 

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