The Unexpected Non-Functional Pancreatic Cyst

Abstract

The diagnosis of cystic tumors of the pancreas can pose a major challenge. Pancreatic neuroendocrine tumors (PNET) represent 1%-2% of all pancreatic neoplasms and less than 10% of all PNETs are cystic in nature (cPan-NET). Endoscopic ultrasound (EUS) evaluation with fine-needle aspiration (EUS-FNA) has emerged as integral part of the evaluation of pancreatic cysts. A 58-year-old woman with obesity, hypothyroidism, and non-functional microadenoma was consulted to our service after an abnormal CT scan. Images revealed an incidental 3.1 cm x 2.9 cm hypodense lesion in the tail of the pancreas with thick peripheral enhancement. The patient denied unintentional weight loss, abdominal pain, history of pancreatitis or toxic habits. EUS-FNA depicted a 3 cm x 2.2 cm septated cystic lesion with thick walls and no solid component suggestive of mucinous cystic neoplasm. Cytology exam showed aggregates of epithelial cells with nuclear atypia, small nucleoli and granular chromatin. Immunoperoxidase studies demonstrated atypical cells positive for chromogranin and synaptophysin and negative for pankeratin and neuron specific enolase favoring the diagnosis of cPan-NET. Serum chromogranin and gastrin levels were within normal limits. An indium-111 pentetreotide scan showed no somatostatin avid lesion throughout the whole body. The patient was referred for resection of this non-functional cPan-NET. PNETs are an uncommon pancreatic malignancy. The reported incidence rate is approximately 5 to 10 cases per 1 million persons per year. They typically present as a solid lesion or as large solid tumors with focal areas cystic degeneration. Rarely, as in our case, a purely cystic presentation without a solid component can occur mimicking other pancreatic cystic lesions such as mucinous cystic neoplasms. There are no unique CT or EUS imaging features for cPan-NET although others have suggested that c-Pan-NETs exhibit thicker walls than mucinous neoplasms. The sensitivity of pentetreotide scans for all PNETs ranges from 70-90% but varies with tumor type and diminishes particularly for sub-centimeter lesions. Aspiration of cyst fluid via EUS-guided FNA provides an important advantage to establish an accurate diagnosis through immunocytology with staining of neuroendocrine markers. Whether solid, solid-cystic or purely cystic, functional or non-functional, all PNETs have a malignant potential and surgery is the only curative treatment.