Ga-DOTATATE PET/CT: How is it reliable in imaging of cases having clinical suspicion of insulinomas?

Purpose: This retrospective study evaluates the value of Ga-DOTATATE PET/CT in the diagnosis and localization of insulinomas, whether sporadic, malignant or MEN-1 associated insulinoma.

Method: The study included 43 patients, having clinical (symptomatic hypoglycemia) and/or laboratory suspicion of having insulinoma (72 h fasting test with serum insulin ≥18 pmol/L), with available pre-operative Ga-DOTATATE PET/CT and CE-CT, and diagnosed with insulinoma confirmed by post-operative histopathology. Preoperative imaging was retrospectively analyzed by two radiologists who were blinded to the final diagnosis and to the results of other imaging modalities. Histopathology of specimen was considered the reference standard, and head-to-head comparison of preoperative CE-CT and PET imaging findings. Findings were classified as true positive (TP), true negative (TN), false positive (FP), and false negative (FN) for each modality. Based on these results, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of CE-CT, and Ga-DOTATATE PET/CT for the detection of insulinoma were calculated.

Results: 43 patients (N = 43 patients, L = 56 lesions), out of these, 37 patients had benign sporadic insulinoma (N = 37, L = 42), only 3 patients had malignant sporadic insulinoma (N = 2, L = 9), and 3 patients had MEN-1 syndrome associated insulinoma (N = 3, L = 5). There was no significant statistical difference in sensitivity (P = 0.3058) and PPV (P = 0.5533) for insulinoma localization in the overall cohort with Ga-DOTATATE PET/CT (87.5 %, 90.74 %) compared to CE-CT (80.36 %, 93.75 %).

Conclusion: Ga-DOTATATE PET/CT is a non-invasive imaging modality that can identify most insulinomas. Still, it offers limited additional information when the tumor is localized by other anatomic imaging studies, so should be used as an adjunct when imaging studies fail to localize the tumor in insulinoma patients, especially when minimally invasive surgical is intended.