Endoscopic Ultrasound (EUS) Decodes Invisible 12-mm Pancreatic Insulinoma in Patient with Tirzepatide History
Background
Diagnosing small pancreatic neuroendocrine tumors (PNETs) like insulinomas can be challenging, as they often cause recurrent symptomatic hypoglycemia but may be missed by conventional cross-sectional imaging like CT. This diagnostic gap delays crucial surgical intervention. Endoscopic ultrasound (EUS) is a highly sensitive modality for detecting these elusive masses and facilitating tissue biopsy. This case highlights EUS's utility in a patient with persistent hypoglycemia and a history of tirzepatide use, where initial CT imaging was negative.
Study Design
A 61-year-old woman presented with recurrent symptomatic hypoglycemia, confirmed by continuous glucose monitoring. Her medical history included remote tirzepatide use for weight loss. Mixed-meal testing showed inappropriately normal insulin/C-peptide and high proinsulin. Initial contrast-enhanced CT of the abdomen was negative for pancreatic masses. Due to high clinical suspicion for insulinoma, EUS was performed, identifying a 12-mm hypoechoic mass in the pancreatic body. EUS-guided fine needle biopsy confirmed a well-differentiated, WHO grade 1 pancreatic neuroendocrine tumor consistent with insulinoma via immunostaining.
Results
The patient exhibited recurrent, predominantly postprandial hypoglycemic episodes, confirmed by continuous glucose monitoring. Four months after discontinuing tirzepatide, mixed-meal testing revealed inappropriately normal insulin and C-peptide levels, alongside a high proinsulin level, strongly indicative of endogenous insulin overproduction. Crucially, initial contrast-enhanced computed tomography (CT) of the abdomen and pelvis was negative for any pancreatic masses.
Endoscopic ultrasound (EUS)successfully identified a 12-mm hypoechoic mass located in the pancreatic body, which was completely missed by CT.EUS-guided fine needle biopsysubsequently confirmed this mass as a well-differentiated, World Health Organization (WHO) grade 1 pancreatic neuroendocrine tumor with immunostaining consistent with insulinoma. Following pancreatic tumor enucleation, the patient experienced complete resolution of her symptoms, confirming the diagnosis and efficacy of surgical intervention.
Key Findings
- EUS identified a 12-mm hypoechoic mass in the pancreatic body, missed by initial CT imaging.
- Patient presented with recurrent symptomatic hypoglycemia, confirmed by continuous glucose monitoring.
- Mixed-meal testing showed inappropriately normal insulin/C-peptide and high proinsulin levels.
- Biopsy confirmed a well-differentiated, WHO grade 1 pancreatic neuroendocrine tumor (insulinoma).
- Surgical enucleation of the tumor resulted in complete resolution of the patient's symptoms.
Why It Matters
This case underscores the critical importance of pursuing advanced imaging like EUS when clinical and biochemical evidence strongly suggests an insulinoma, even if initial cross-sectional imaging like CT is negative. For clinicians, it reinforces EUS as an indispensable diagnostic tool for small, 'invisible' pancreatic neuroendocrine tumors, enabling timely and definitive surgical management. The patient's remote history of tirzepatide use, while not implicated in causing the tumor, highlights the need for thorough diagnostic workup for persistent symptoms, regardless of prior medication history. This approach ensures that patients with endogenous hypoglycemia receive accurate diagnosis and curative treatment, preventing prolonged morbidity.
insulinoma
neuroendocrine-tumor
hypoglycemia
endoscopic-ultrasound
eus
case-report