Primary Mesenteric Neuroendocrine Tumor: A Rare Case of Aggressive Progression

Abstract

Mesenteric neuroendocrine tumors (NETs) are generally secondary localizations of small intestine tumors. However, primary mesenteric forms are rare. We report the case of a 75-year-old patient who had been experiencing cholestatic jaundice for a month, along with epigastric pain. Initial imaging revealed a pancreatic neoplasm located at the uncinate process, with dilation of the common bile duct and the Wirsung duct. However, endoscopic ultrasound rather suggested early-stage chronic pancreatitis, without an identifiable mass. Abdominal MRI revealed a 55 × 33 mm mesenteric lesion with spiculated and retractile borders, encasing the superior mesenteric vessels and distant from the pancreatic uncinate process. Its radiological characteristics were suggestive of a mesenteric carcinoid tumor. Suspected metastatic liver nodules, retroperitoneal lymphadenopathy, and pancreatic atrophy with mild ductal dilation were also present. Laparotomy revealed a 10 cm mesenteric mass infiltrating the mesenteric vessels, making surgical resection impossible. No primary tumor of the small intestine or pancreas was identified. Histological analysis confirmed a well-differentiated grade 1 neuroendocrine tumor, with a proliferation index <1% and strong diffuse expression of chromogranin A, synaptophysin, and cytokeratin AE1/AE3. The patient’s case was discussed in a multidisciplinary board meeting, in which chemotherapy was decided and initiated. Despite this low proliferation index, the tumor progressed aggressively, with liver, lymph node, and pleural metastasis, as well as peritoneal carcinomatosis. This case highlights the occasionally aggressive evolutionary potential of primary mesenteric neuroendocrine tumors, even of low grade.