A 53-year-old woman with small stature and dysmorphic features consistent with TS, not previously diagnosed with diabetes, presented to the endocrinology clinic for evaluation of episodes of hypoglycemia <20mg/dl with transient loss of consciousness. She was admitted to the inpatient service and underwent a controlled 72h fast. After 64h, she developed hypoglycemia to the low 30s mg/dl with mild neuroglycopenic symptoms (emotional outbursts). Biochemical workup showed unsuppressed insulin levels (1.2mIU/L), markedly elevated proinsulin (30 pmol/L), and BOHB levels (6500mumol/L).
MR and multiphase CT (Figure 1) showed a solid, hyperenhancing 2.5cm pancreatic tail mass with slow washout. 111In-pentetreotide (Octreoscan) study (Figure 2) demonstrated absence of radiotracer uptake ruling out a splenule. CT guided fine needle biopsy of the mass confirmed neuroendocrine etiology. Since Octreoscan sensitivity is not high, hepatic vein blood sampling after intra-arterial calcium stimulation was further performed and showed robust increase of insulin (9.4 to 17.8mIU/L) and proinsulin (7pmol/L to 20pmol/L) and high c-peptide levels at the distal splenic artery, consistent with insulinoma of the tail of the pancreas.
Surgical excision of the mass resulted in complete resolution of symptoms up to 3 years postop. Histologic examination confirmed a well differentiated neuroendocrine tumor with immunostainings positive for chromogranin and synaptophysin and a KI index of <2%.