Insulinoma in a 33 year old woman – challenges in functional localisation.
Matthew Allum, James Jackson, Adil Al-Nahhas, Jeannie Todd
Imperial Centre for Endocrinology, Hammersmith Hospital, Imperial College NHS Trust, London, UK
A 33 year old female presented with 9 months of episodes of lethargy, poor concentration, slurred speech and sweating, especially on waking. Symptoms were relieved by eating, especially honey and she had gained 15kgs in weight over the period. She had no relevant past medical or family history. She was found to have low capillary blood glucose and referred for investigation of hypoglycaemia. Symptoms were difficult to control by eating alone, particularly at night.
The patient was admitted for a supervised fast and developed hypoglycaemic after 8 hours with a glucose of 2.0 mmol/L, insulin inappropriately elevated insulin at 15.2 mU/L (NR <3.0) and C-peptide of 920 pmol/L (NR <300). Sulfonylurea screen was negative and therefore the results are consistent with insulinoma.
She had several radiological interventions in an attempt to localise a functional tumour. Arterial phase CT scan of the abdomen revealed a 12 mm arterially enhancing lesion in the head of the pancreas. However gallium Dotatate whole-body PET CT scan failed to demonstrate a gallium-avid lesion. Therefore she underwent arterial calcium stimulation with hepatic venous sampling. Proximal superior mesenteric, splenic, proper hepatic and gastroduodenal (GDA) arteries were injected with calcium gluconate. However, although there was a blush following injection of the GDA, this did not show any significant elevation in insulin or C-peptide after venous sampling from the right hepatic vein and the test was therefore negative. This was considered to be secondary to arterial spasm on injection of the GDA. The test did however demonstrate that there was not an additional source of insulin from within the pancreas.
Subsequent endoscopic ultrasound showed a 12mm hypoechoic lesion in the head of the pancreas. In conclusion, in this particular case, functional imaging and calcium stimulation with venous sampling failed to localise an insulin secreting lesion.
Two modalities of functional testing have been negative. It is probable that the calcium stimulation test was negative in this case due to spasm in the GDA, which did not allow calcium to reach the tumour. In this case no further functional testing has been planned, as the CT scan, visceral angiogram and ultrasound images show a defined pancreatic tumour with the characteristic features of a NET and she has unequivocal biochemistry. The subsequent Neuro-Endocrine Tumour MDT discussion has suggested we should proceed to laparoscopic removal of the insulinoma.