An insulinoma is a tumor in the pancreas that produces too much insulin.
Insulinoma; Islet cell adenoma, Pancreatic neuroendocrine tumor; Hypoglycemia - insulinoma
The pancreas is an organ in the abdomen. The pancreas makes several enzymes and hormones, including the hormone insulin. Insulin's job is to reduce the level of sugar (glucose) in the blood by helping it move into cells.
Most of the time when your blood sugar level drops too low, the pancreas stops making insulin until your blood sugar returns to normal. Tumors of the pancreas that produce too much insulin are called insulinomas. Insulinomas keep making insulin, even when your blood sugar drops too low.
A high blood insulin level causes a low blood sugar level (hypoglycemia). Hypoglycemia may be mild, leading to symptoms such as anxiety and hunger. Or it can be severe, leading to seizures, coma, and even death.
Insulinomas are rare tumors. They usually occur as single, small tumors. But there can also be several small tumors.
Most insulinomas are non-cancerous (benign) tumors. People with certain genetic disorders such as multiple endocrine neoplasia type I are at risk for insulinomas.
Symptoms are most common when you skip or delay a meal. Symptoms may include:
- Anxiety, behavior changes, or confusion
- Clouded vision
- Loss of consciousness or coma
- Convulsions or tremor
- Dizziness or headache
- Hunger or weight gain
- Fast heart rate
Exams and Tests
After fasting, your blood may be tested for:
- Blood C-peptide level
- Blood glucose level
- Blood insulin level
- Drugs that cause the pancreas to release insulin
- The response of your body to a shot of glucagon
- Endoscopic ultrasound (test that uses a flexible scope and sound waves to view digestive organs)
- Octreotide scan (special test that checks for cancer cells in the body)
- Pancreatic arteriography (test that uses special dye to view the arteries in the pancreas)
- Pancreatic venous sampling for insulin (test that helps locate the exact location of the tumor that is making too much insulin)
Surgery is the usual treatment for insulinoma. If there is a single tumor, it will be removed. If there are many tumors, part of the pancreas will need to be removed. At least 15% of the pancreas must be left to produce its enzymes for digestion.
In rare cases, the entire pancreas is removed if there are many insulinomas or they continue to come back. Removing the entire pancreas leads to diabetes because there is no longer any insulin being produced. Insulin shots (injections) are then required.
If no tumor is found during surgery, or if you can't have surgery, you may get the medicine diazoxide to lower insulin production and prevent hypoglycemia. A water pill (diuretic) is given with this medicine to prevent the body from retaining fluid. Octreotide is another medicine that is used to reduce insulin release in some people.
In most cases, the tumor is non-cancerous (benign), and surgery can cure the disease. But a severe hypoglycemic reaction or the spread of a cancerous tumor to other organs can be life-threatening.
Complications may include:
- Severe hypoglycemic reaction
- Spread of a cancerous tumor (metastasis)
- Diabetes if the entire pancreas is removed (rare)
- Inflammation and swelling of the pancreas
When to Contact a Medical Professional
Call your health care provider if you develop any symptoms of insulinoma. Seizures and losing consciousness are an emergency. Call 911 or your local emergency number right away.
Jensen RT, Norton JA, Oberg K. Neuroendocrine tumors. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology/Diagnosis/Management. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 33.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Neuroendocrine tumors. Version 2.2016. www.nccn.org/professionals/physician_gls/pdf/neuroendocrine.pdf. Accessed August 18, 2016.
Schneider DF, Mazeh H, Lubner SJ, Jaume JC, Chen H. Cancer of the endocrine system. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff's Clinical Oncology. 5th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2014:chap 71.
Reviewed By: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.