A rare case of mimicry of insulinoma: presenting mainly in terms of clinical symptoms, imaging and molecular markers

Background Nesidioblastosis and insulinomas are caused by dysfunctional β cells, which in turn can cause endogenous hyperinsulinemia. In adults, the clinical and histomorphological features of nesidioblastosis and insulinoma may be remarkably similar, implying that it can be difficult to differentiate the two entities with preoperative biochemical and diagnostic imaging. Case presentation We report a 48-year-old man diagnosed with adult focal nesidioblastosis. We used contrast-enhanced magnetic resonance imaging (ceMRI), [68Ga]-DOTATATE positron-emission tomography/computed tomography (PET/CT), endoscopic ultrasonography (EUS)-guided fine-needle aspiration (FNA) and other tests before surgery, all of which highly suggested insulinoma. However, the final pathological diagnosis was focal neuroblastoma. Conclusion Adult focal nesidioblastosis is very rare. In this case, we focused on differentiating focal nesidioblastosis from insulinoma. We reviewed relevant literature reports and found that it is sometimes difficult to differentiate the two diseases with the results of preoperative examinations. For pancreatic space-occupying lesions that can clinically present as either of these two diseases, the focus should be on distinguishing between the presence and absence of metastases as well as precise pancreatic localization.