How is an insulinoma diagnosed?

John A. Chabot
Endocrinology Diabetes & Metabolism

Diagnosis for insulinomas requires observation of insulin level as it relates to blood sugar level. A low blood sugar level combined with a high insulin level confirms the diagnosis that an insulinoma exists. After diagnosis, the next step is localization of the tumor, accomplished using imaging studies including CT, MRI, octreotide scanning (injection of radioisotope into the vein and subsequent scanning to record the radiation given off by the radioisotope), and ultrasound. However, in some patients, these imaging techniques are unable to localize the tumor. In these cases, attempts to locate the lesion are performed by experienced endocrine surgeons during an operation and are successful in the majority of patients.

Virtually all insulinomas are located within the pancreas. Because these tumors are usually small, sometimes only 1/3 of an inch in diameter, locating these tumors may be elusive even using the best modern-day techniques. Which and in what order localization methods are chosen often depends on the equipment and expertise available at any particular institution. A sequential manner is usually elected, proceeding from the least complicated and generally less expensive, to more complex methods that may require more cooperation by the patient and often are more expensive.