Endocrine Abstracts

Introduction: 80–90% of insulinomas are smaller than 2 cm, equally located in the head, body and tail of pancreas. Computer tomography (CT) is 75%, magnetic resonance imaging (MRI) is 55–90%, endoscopic ultrasonography (EUS) is 85–95% and selective arterial calcium stimulation test (SACST) is 95–100% sensitive in the diagnosis of insulinomas. Here, we presented two cases of insulinoma which could not be located by conventional methods and evaluated with SACST.

Case 1: A 29-year-old male who described hypoglycemic symptoms especially after exercise in the last 4 months was admitted to the hospital for a prolonged fasting test. At the 8th hour of the test, laboratory results were as follows; blood glucose 36mg/dl, insülin 21 uIU/dl, c-peptide 4 ng/dl, proinsulin 22 pmol/l and cortisol 18 ug/dl. Blood ketone and anti-insulin antibody were negative. No pathology was observed in the abdominal CT and EUS. Abdominal MRI revealed a 10 mm diameter nodular lesion in the posterior medial of the stomach which was suspicious for insulinoma. It was seen only in T2A sequence in the venous phase in contrast-enhanced examination. Galium-68 Dotatate scintigraphy showed no involvement in the pancreas. SACST was performed. A ten-fold increase in insulin levels was observed in the splenic artery and distal pancreatectomy was performed.

Case 2: A 41-year-old woman who had episodes of hypoglycemia for 3–4 months was referred with a pre-diagnosis of insulinoma. The patient underwent a prolonged fasting test. At the time of hypoglycemia (blood glucose 45 mg/dl), serum insülin was 7.8 uIU/dl, c-peptide was 2.2 ng/dl, proinsulin was 8 pmol/l and, serum ketone and anti-insulin antibody were negative. There was no contrast enhancement in the pancreas in the abdominal MRI, but a suspicious hyperintense area of 10 mm diameter was seen in T2A sequence. There was no pathology in abdominal CT and EUS. In SACST, a five-fold increase in insulin levels was detected in the mesenteric artery which was suggestive for an insulinoma lesion in the head of pancreas. Surgical excision was recommended but the patient refused.

Conclusion: Although the biochemical diagnosis of insulinomas are usually not complicated, the localization might be problematic. Because of the low sensitivity of non-invasive methods in tumors smaller than 2 cm, invasive methods can be used for the localization like in our cases.