SAT-082 - Recurrent Insulinoma Presenting with Negative Initial Imaging

Functional pancreatic neuroendocrine tumors (PNETs) may secrete a variety of hormones, most commonly insulin. Insulinomas are rare, with an incidence of approximately 1–4 cases per million annually [1]. Patients typically present with persistent hypoglycemia due to endogenous hyperinsulinism.

We present a case of recurrent insulinoma in a 55-year-old man. Seven years prior, he presented with dizziness and lightheadedness and was found to have hypoglycemia with a blood glucose of 46 mg/dL. Laboratory evaluation demonstrated elevated insulin (22.5 µIU/mL) and C-peptide (3.04 ng/mL). Computed tomography (CT) revealed an enhancing pancreatic mass, and he underwent distal pancreatectomy. Pathology confirmed a well-differentiated PNET measuring 4.5 × 3.4 × 3.4 cm with three positive lymph nodes (Ki-67 < 3%) and negative surgical margins (3 mm). His symptoms resolved, and glycemic control remained normal for seven years.

The patient presented again with recurrent lightheadedness and severe hypoglycemia, requiring intravenous dextrose. During hypoglycemia (47 mg/dL), laboratory studies demonstrated inappropriately normal to high insulin (6.3 µIU/mL), C-peptide (3.1 ng/mL), and proinsulin (25.3 pmol/L), with negative insulin antibodies. Initial contrast-enhanced CT and MRI failed to localize a lesion. Given persistent clinical suspicion, multidisciplinary discussion prompted repeat CT imaging, which revealed a subtle, non-enhancing 3.4 × 3.0 cm mass adjacent to the prior surgical suture line. Segmental pancreatectomy was performed. Pathology confirmed recurrent well-differentiated PNET (3.3 × 3.0 × 2.6 cm) with lymphovascular invasion, negative margins, Ki-67 < 3%, and positive chromogranin and synaptophysin staining. Postoperatively, hypoglycemia resolved and hormone levels normalized.

This case highlights the diagnostic challenges of recurrent insulinoma, particularly when imaging findings are subtle or atypical. While PNETs typically demonstrate enhancement on imaging, this recurrence did not. Management options include medical therapy with diazoxide and octreotide or surgery. Tumor recurrence after surgery is usually associated with malignancy or positive margins. This patient’s prior insulinoma was found to be benign with negative margins, thus recurrence is unexpected but it should remain an important consideration in patients with prior insulinomas. This case underscores the importance of maintaining clinical suspicion, prioritizing biochemical evidence, and utilizing multidisciplinary collaboration to guide diagnosis and management.

[1] Johannes Hofland, Julie C Refardt, Richard A Feelders, Emanuel Christ, Wouter W de Herder, Approach to the Patient: Insulinoma, The Journal of Clinical Endocrinology & Metabolism, Volume 109, Issue 4, April 2024, Pages 1109–1118

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