Schwannoma Likely Arising from the Pancreatic Head Nerve Plexus That Mimicked a Mucinous Cystic Neoplasm and Was Treated by Pancreaticoduodenectomy: A Case Report.

Pancreatic and peripancreatic schwannomas are exceptionally rare benign peripheral nerve sheath tumors. Cystic and hemorrhagic degeneration may produce imaging findings resembling pancreatic cystic neoplasms, while an extrapancreatic neural origin can be difficult to recognize preoperatively. Lesions located in the pancreatic head nerve plexus region pose additional surgical challenges because of their close relationship with periarterial nerve plexuses and major vessels. A 48-year-old woman was referred for a 5-cm multilocular cystic lesion adjacent to the pancreatic head. CT, MRI, and endoscopic ultrasonography showed a thick-walled multilocular cystic mass with enhancing septa and solid components, hemorrhagic change, no communication with the main pancreatic duct, and marked displacement of peripancreatic vessels. An MCN-like cystic neoplasm with malignant potential was suspected. Endoscopic US-guided tissue acquisition was not performed because puncture-related dissemination was a concern. Pancreaticoduodenectomy was selected because malignancy could not be excluded and safe local excision was considered technically difficult. Intraoperatively, the tumor was well demarcated from the pancreatic parenchyma but firmly adherent to the periarterial nerve plexus around the common hepatic artery, celiac axis, splenic artery, and superior mesenteric artery. A replaced right hepatic artery was in broad contact with the tumor and was resected en bloc with the tumor and reconstructed. The tumor was removed without capsular rupture. Histopathological examination showed a spindle cell neoplasm with cystic and hemorrhagic degeneration located in the pancreatic head nerve plexus region, with the surrounding nerve plexus tissue around the tumor and no epithelial lining. Immunohistochemistry showed diffuse positivity for S-100 protein and SRY-box transcription factor 10 (SOX10) and negativity for c-kit, discovered on gastrointestinal stromal tumor 1 (DOG1) CD34, α-SMA, desmin, and pan-cytokeratin AE1/AE3 (AE1/AE3), supporting the diagnosis of schwannoma likely arising from the pancreatic head nerve plexus. The postoperative course was uneventful. A schwannoma located in the pancreatic head nerve plexus region may mimic an MCN-like cystic neoplasm and make periarterial dissection technically demanding. When clinically appropriate and safely feasible, EUS-guided tissue acquisition may be considered because a preoperative diagnosis may permit observation or organ-preserving surgery. Pancreaticoduodenectomy may be selected when malignancy cannot be excluded and safe local excision is not feasible because of firm periarterial adhesion.