[(68)Ga-exendin-4 PET-CT for the localization of occult insulinomas: a prospective cohort study]

Objective: To explore the accuracy in localizing occult insulinomas with Glucagon-like peptide-1 receptor(GLP-1R) PET-CT with (68)Ga-exendin-4. Methods: In this prospective cohort study, patients with biochemically proven endogenous hyperinsulinemic hypoglycemia and negative contrast-enhanced CT with pancreatic perfusion scans were enrolled consecutively at Department of Nuclear Medicine, Peking Union Medical College Hospital from February 2014 to June 2018.There were 37 males and 32 females, with age of (43.2±17.9)years. (68)Ga-exendin-4 PET-CT, MRI and endoscopic ultrasound(EUS) were done before elective surgery. Sensitivity, specificity, accuracy, positive predictive value(PPV) and negative predictive value(NPV) of the above imaging modalities were calculated. Results: A total of 69 patients were recruited. Thirty-two patients were diagnosed with insulinomas at histology. Four patients with positive (68)Ga-exendin-4 PET-CT findings did not undergo surgery so far. Twenty-eight patients were proven to be noninsulinoma induced hyperinsulinemic hypoglycemia. Five patients were unknown of etiology of hypoglycemia. The sensitivity, specificity, accuracy, PPV and NPV of (68)Ga-exendin-4 in localizing occult insulinomas were 96.9%(31/32), 100%(30/30), 98.3%(59/60), 100%(29/29), 96.8%(30/31), respectively.The sensitivity, specificity, accuracy, PPV and NPV of MRI were 74.1%(20/27), 9/11, 76.3%(29/38), 90.9%(20/22), 9/16, respectively. The sensitivity, specificity, accuracy, PPV and NPV of EUS were 75.0% (15/20), 2/2, 77.3%(17/22), 15/15, and 2/7. Conclusion: (68)Ga-exendin-4 PET-CT has a high sensitivity, specificity and accuracy for detection of occult insulinoma, which shows superiority to MRI and EUS.