Plexiform schwannoma of the duodenum accompanying pyloric stenosis: report of a case.

Plexiform schwannoma is a benign peripheral nerve sheath tumor and is composed of Schwann cells arranged in a plexiform pattern. Most plexiform schwannomas are skin tumors, and there has been no case report of this tumor originating in the duodenum. We describe the first known case of plexiform schwannoma of the duodenum. A 60-year-old man presented with a short history of food intolerance, epigastric discomfort, fullness and bloatedness, sometimes vomiting, and weight loss, without any clinical picture of neurofibromatosis. Upper gastrointestinal endoscopy revealed pyloric stenosis with normal mucosal lining. The computed tomography demonstrated circumferentially and concentrically thickened pylorus up to 18 mm with narrowed lumen and limited contrast passage. Antrectomy and gastrojejunostomy were performed due to unknown etiology of the obstruction. The cut surface of the lesion revealed thickened pylorus up to 15 mm in a circumferential manner. It contained a 5 mm tumor consisted of multiple white nodules in the submucosal and subserosal layers with overlying duodenal mucosa. Microscopic examination revealed nodular structures composed of spindle cells within fascicular pattern without any atypia or mitosis. Immunohistochemical examination revealed that the cells diffusely and strongly expressed S100 proteins in a nuclear and cytoplasmic pattern, but not CD117, smooth muscle actin, desmin, or CD34, confirming plexiform schwannoma.