LAUSR

We report two cases of an uncommon benign lesion, retroperitoneal ganglioneuroma, first diagnosed on fine needle aspiration (FNA) cytology. Our first case presented with nausea, constipation, vomiting, and neutropenia after three cycles of chemotherapy for breast cancer treatment, while our second patient presented with seemingly unprovoked abdominal pain and progressive neuropathy. Both underwent computed tomography (CT) scans, in which a soft tissue mass was found in the retroperitoneal space in each patient. An endoscopic ultrasound guided (EUS) FNA was performed on both patients, and as a result, the masses were diagnosed as retroperitoneal ganglioneuromas. As retroperitoneal ganglioneuromas have low incidence of proliferation, invasive surgery was avoided in favor of routine follow‐up imaging. Cytologically, both masses showed large, scattered ganglion cells with abundant cytoplasm and large nuclei against a background of wavy spindle cells with elongated nuclei. Histologically, both were positive for S‐100. When an EUSFNA is performed and quality material is collected, a diagnosis of retroperitoneal ganglioneuroma may be established, preventing invasive surgery and its accompanying risks in favor of routine follow‐up imaging.