Giant pancreatic tumor with clinical characteristics of insulinoma but without common pathologic features.

Objective: To report a case of a large pancreatic tumor that had clinical characteristics of an insulinoma without classic pathologic features.
Methods: We describe a 58-year-old woman who presented with a 3-month history of symptomatic hypoglycemic episodes, which were characterized by confusion. The laboratory, imaging, and pathologic findings are summarized, the current literature on giant insulinomas is reviewed, and the distinction between clinical and pathologic diagnosis of neuroendocrine tumors is discussed.
Results: The biochemical diagnosis of insulinoma was established with concomitant low fasting blood glucose concentrations and inappropriately high insulin levels. An abdominal computed tomographic scan revealed a mass (10 by 11.7 by 9.7 cm) in the head and body of the pancreas, which was resected. Pathologic examination revealed a massive neuroendocrine tumor (13.5 by 11 by 8 cm) without immunohistochemical evidence of insulin expression. Nevertheless, tumor resection resulted in decreased blood insulin levels and resolution of the patient's hypoglycemia.
Conclusion: Although more than 95% of insulinomas are smaller than 3 cm, this case is unique in that the extremely large pancreatic tumor had clinical characteristics of an insulinoma but did not have the classic pathologic findings. Because of the extensive pancreatic resection, the patient is dependent on both insulin and orally administered pancreatic enzymes but remained free of symptoms and disease recurrence at 1-year follow-up.