Circularity of islets is a distinct marker for the pathological diagnosis of adult-onset nesidioblastosis in surgical specimens

Abstract Background Nesidioblastosis is a rare cause of endogenous hyperinsulinemic hypoglycemia in adults (adult-onset nesidioblastosis). This disease is characterized by diffuse hyperplasia of pancreatic endocrine cells and diagnosed by a pathological examination. The diagnostic criteria of this disease have been proposed, and we established more quantitative criteria for evaluating islet morphologies. Methods We measured the numbers, maximum diameters, total areas, and circularities (representing how closely islets resemble perfect spheres) of islets contained in representative sections of adult-onset nesidioblastosis (n = 4) or control cases (n = 5) using the NIS-Elements software program. Results There was no significant difference in the numbers, maximum diameters, and total areas of the islets between the two groups, even after correcting these parameters per unit of area. However, the number of islets with low circularities (< 0.71) per total area of pancreatic parenchyma was significantly larger in the adult-onset nesidioblastosis specimens than in the controls. Conclusions Low circularity, which indicates an irregular islet shape, referred to as "irregular shape and occasional enlargement of islets” and “lobulated islet structure" in the previous report, is a useful marker for diagnosing nesidioblastosis.