Endocrine Abstracts

Introduction: Insulinoma is a rare neuroendocrine tumor that is difficult to diagnose due to its obscure location. Conventional radiographic methods have low sensitivity and are inadequate to detect insulinoma. Selective arterial calcium stimulation test (SACST) is 95–100% sensitive in the diagnosis of insulinomas. Here, we presented two cases of insulinoma that could not be located by radiographic methods and evaluated them with SACST.

Case 1: A 48-year- old woman who had dizziness was referred to our endocrine clinic with a suspicion of insulinoma. A 72-hour fasting test was performed to establish a diagnosis of endogenous hyperinsulinemia. After 19 h hypoglycemic symptoms emerged and fasting serum glucose (FSG) was 27 mg/dl, insulin 6,5 mU/l, and C-peptide 2 µg/l. MRI of the abdomen, Galium-68 Dotatate scintigraphy, and endoscopic ultrasonography (EUS) failed to detect the tumor. SACST was performed to localize the tumor. Calcium injection of the gastroduodenal artery caused a more than 11-fold increase in hepatic insulin above baseline indicating a lesion in the head region of the pancreas. Intraoperative ultrasonography of the pancreas revealed a 1 cm nodular lesion in the head. Proximal pancreatectomy was performed. Histopathological findings were consistent with well-differentiated neuroendocrine tumor showing positive staining with synaptophysin and chromogranin. After surgery, the patient was free of all previous symptoms.

Case 2: A 67-year- old woman was admitted to the clinic due to dizziness and diaphoresis. She applied to the emergency department once with a loss of consciousness. There was a weight gain of 4-5 kg during this period. After 12 h of the 72-hour fasting test, hypoglycemic symptoms emerged, and FSG was 36 mg/dl, insulin 6,9 mU/l, and C-peptide 1,7 µg/l. MRI of the abdomen, Galium-68 Dotatate scintigraphy, and EUS failed to demonstrate the tumor. SACST was performed and calcium injection of the splenic artery caused a more than 9-fold increase in hepatic insulin above baseline which was suggestive of an insulinoma lesion in the tail of the pancreas. Intraoperative ultrasonography of the pancreas revealed a 1 cm nodular lesion in the tail. Distal pancreatectomy was performed. No hypoglycemia has occurred since the surgery.

Conclusions: The localization of insulinoma is critical for curative surgery and might be problematic. Because of the low sensitivity of non-invasive imaging procedures in tumors smaller than 2 cm, invasive methods can be used for the localization like in our cases.