6538 Find me if you can! A Case of a "Well Placed Solitary Insulinoma" in "The Center" of an SACST

Abstract Disclosure: R. Kennedy: None. D.A. D'Alessio: None. A.V. Vella: None. Introduction: Selective arterial calcium stimulation testing (SACST) can be utilized in patients to localize solitary insulinomas when imaging is non diagnostic. While a heterogenous stimulation pattern suggests NIPHS, or multiple insulinomas this case uniquely demonstrates such a pattern with a solitary insulinoma. Clinical Case: The patient is a 48 year old female who presented to the emergency department (ED) for bizarre behavior which resolved with a sweetened drink. Serum glucose was 62 mg/dL, she was treated with IV dextrose and was discharged from the ED. She was referred to outpatient endocrinology for further evaluation where continuous glucose monitoring confirmed predominantly fasting hypoglycemia. Adrenal insufficiency was excluded. She was admitted for a 72 hour inpatient fast where the patient achieved hypoglycemia within 24 hours, with glucose 46 mg/dL (associated with neuroglycopenic symptoms), beta hydroxybutyrate < 0.18 mmol/L, insulin 3.9 mcIU/mL, proinsulin 157pmol/L, c-peptide 1.4 ng/mL and a glucose rise greater than 25mg/dL after glucagon administration. Sulfonylurea screen and insulin antibodies were negative; IGF1 within normal limits. These labs were consistent with hyperinsulinemic hypoglycemia. An MRI pancreas however did not reveal an insulinoma. The patient therefore underwent a SACST, demonstrating a 10 fold response in the territory of the gastroduodenal artery and splenic artery, as well as a 3 fold response in the superior mesenteric artery. This heterogenous pattern in addition to the marked response in each arterial territory raised the possibility of multiple insulinomas. However as there were no tumors present on imaging, medical management was initiated with close follow up. She was trialed with months of somatostatin analogs and diazoxide with minimal improvement in the frequency and severity of her hypoglycemia. About a year after her initial diagnosis, repeat abdominal imaging (CT and MRI) revealed an 8 mm arterial hyper-enhancing lesion in the body of the pancreas concerning for neuroendocrine tumor. Repeat SACST was performed, this time showing a greater than 10 fold response in all three arterial territories. Angiography showed a tumor blush that was visible when each of the three major arteries were injected sequentially. She underwent laparoscopic pancreatic enucleation. The lesion was located on the body of the pancreas, with histology confirming an insulinoma. The patient responded promptly post operatively; her symptoms resolved without further need of medical management. Conclusion: Our case shows that the interpretation of an SACST should take into account the arterial anatomy before ascribing a non-focal response to multiple territories of insulin hypersecretion. Presentation: 6/1/2024