Insulinoma

Glucose is the monitor - Check point-of-care glucose frequently from induction through emergence. Hypoglycemia is a venous glucose under 55 mg/dL, and under anesthesia the patient cannot report the palpitations, tremor, diaphoresis, blurred vision, or confusion that would normally warn you. Amnesia for the hypoglycemic event is common even in awake patients.

Do not let them fast long - Fasting hypoglycemia is the characteristic presentation in 73% of patients, and another 20% have both fasting and postprandial episodes. Book them early, keep the NPO window short, and run dextrose-containing fluid while they wait.

Preoperative medical control - Diazoxide decreases insulin release and enhances glycogenolysis, and about 60% of patients become symptom-free on it. Octreotide and other somatostatin analogs are the fallback when diazoxide fails. Patients can be treated preoperatively with diazoxide or a somatostatin analog as tolerated — confirm what they took and when.

The diagnostic numbers you will see in the chart - The 72-hour fast is the gold standard: plasma glucose under 55 mg/dL with insulin at or above 3 microunits/mL, C-peptide at or above 0.6 ng/mL, proinsulin at or above 5 pmol/L, beta-hydroxybutyrate at or below 2.7 mmol/L, and a simultaneously negative sulfonylurea screen.

Screen for MEN1 - Genetic testing is recommended for every young patient with insulinoma, and MEN1 should be suspected with a personal or family history of endocrinopathy. Hyperparathyroidism appears in 90% of MEN1 — check a serum calcium and intact PTH — and pituitary adenoma in 40%, so ask about visual field changes and look at the neck and abdomen on exam.

Localization procedures you may be sedating for - CT with contrast finds 70% to 80% of tumors, MRI about 85%, and endoscopic ultrasound 70% to 95%, which beats CT and allows tissue sampling. Selective arterial calcium stimulation with hepatic venous sampling has 93% sensitivity and is reserved for negative imaging or MEN1.

The operation - Enucleation or partial distal pancreatectomy is the usual procedure, increasingly done laparoscopically or robotically with a shorter stay. MEN1 patients may need subtotal pancreatectomy on top of enucleation, so plan for a longer case.

Neuroglycopenia mimics almost anything - Confusion, behavior change, blurred vision, and seizure are all documented presentations, and some patients present with panic attacks or other psychiatric symptoms. Do not write off odd preoperative behavior as anxiety — get a glucose.

Persistent symptoms after resection - Suggest multiple tumors or MEN1 and get repeat imaging. Non-MEN1 patients are followed at 3 to 6 months post-resection with repeat biochemical testing and imaging; multiple-tumor and MEN1 patients are followed yearly even when cured.

Unresectable or metastatic disease - Diazoxide first, octreotide for refractory hypoglycemia, everolimus or sunitinib for progressive pancreatic neuroendocrine tumor. These patients still come to the OR for palliative or unrelated surgery and are still hypoglycemic — the glucose plan does not change.

Insulinoma is a functional pancreatic neuroendocrine tumor that secretes insulin autonomously — it keeps releasing insulin even when plasma glucose is low. The resulting hyperinsulinemia drives glycogen synthesis while suppressing gluconeogenesis and glycogenolysis, so the patient runs out of circulating glucose, classically after a fast. It is usually a single benign tumor; about 5.8% are malignant and 6% to 7.6% sit inside multiple endocrine neoplasia type 1 (MEN1), from a mutation at 11q13. Incidence is 1 to 4 per million per year, with surgery at a median age of 47 to 50. Fasting hypoglycemia is the hallmark, reported in 73%. The perioperative problem is simple: anesthesia erases the sympathoadrenal and neuroglycopenic warning signs, so hypoglycemia proceeds silently toward seizure and neurocognitive injury.