What are the recommended imaging modalities for diagnosing insulinoma?

Insulinoma Imaging

For insulinoma localization, begin with dual-phase multidetector CT or MRI combined with endoscopic ultrasound (EUS), which together achieve near 100% sensitivity for detecting these tumors. 1, 2, 3

Initial Non-Invasive Imaging

• Dual-phase multidetector CT has a sensitivity of 57-94% for pancreatic neuroendocrine tumors and should be performed first to rule out metastatic disease 1, 2
• MRI demonstrates comparable sensitivity of 74-94% and serves as an excellent alternative or complementary modality to CT 1
• These cross-sectional imaging studies are essential for initial assessment and surgical planning, though they may miss small lesions 1

Endoscopic Ultrasound (EUS)

• EUS is highly sensitive (82-93%) and should be performed in all cases where cross-sectional imaging is negative or equivocal 1
• EUS serves dual purposes: tumor localization and tissue sampling via fine needle aspiration, with close correlation between aspiration cytology and final histology 1
• This modality is particularly valuable for detecting small tumors and multiple lesions in MEN1 or VHL syndromes that cross-sectional imaging may miss 1
• The technique is operator-dependent but achieves sensitivities as high as 79-100% in experienced hands 1

Advanced Functional Imaging

• 68Ga-DOTATOC/DOTATATE PET/CT demonstrates the highest sensitivity (87-96%) for pancreatic neuroendocrine tumors and should be considered when conventional imaging is negative 1
• This modality correctly localizes insulinomas in 90% of cases and may identify lesions missed by all other non-invasive studies 4
• Somatostatin receptor scintigraphy (SSRS) has limited utility for insulinomas specifically, with only 50-60% sensitivity, compared to 75% for other pancreatic NETs 1

Invasive Localization Techniques

• Selective arterial calcium stimulation with hepatic venous sampling achieves up to 90% success rate for localizing occult insulinomas and should be reserved for cases where non-invasive imaging fails 1
• This technique regionalizes the tumor to specific pancreatic arterial territories and must be interpreted in combination with other imaging modalities 1

Intraoperative Localization

• Intraoperative ultrasound (IOUS) is mandatory and improves sensitivity to 92-97% for identifying small lesions, particularly in the pancreatic head 1
• IOUS enhances detection beyond all preoperative imaging modalities and serves as a useful adjunct to surgical palpation 1
• Manual palpation identifies insulinomas in 83% of cases but is less sensitive than IOUS for small or deep lesions 4

Recommended Imaging Algorithm

• Start with dual-phase CT or MRI to assess for metastatic disease and initial tumor localization 1, 2
• Add EUS for all patients to improve detection of small tumors and obtain tissue diagnosis 1, 2, 3
• Consider 68Ga-DOTATATE PET/CT when conventional imaging is negative or for minimally invasive surgical planning 2, 4
• Reserve selective arterial calcium stimulation for truly occult cases where all non-invasive studies are negative 1, 2
• Plan for mandatory IOUS at the time of surgery regardless of preoperative imaging results 1, 2

Critical Pitfalls

• Avoid relying solely on SSRS for insulinoma detection, as its sensitivity is only 50-60%, significantly lower than for other pancreatic NETs 1
• Insulinomas are typically small (average 1.65 cm) and may be missed by single imaging modalities, necessitating a multimodal approach 5
• The combination of sonography and MRI achieves 96.6% correct localization, superior to CT with angiography at 72.4% 5
• EUS-guided fine needle tattooing can be used for precise intraoperative localization when laparoscopic ultrasound is unavailable 3