Hybrid Nerve Sheath Tumor Detected by Endoscopic Full‐Thickness Resection for a Gastric Subepithelial Lesion: A Case Report

Hybrid nerve sheath tumors (HNSTs) are exceedingly rare in the gastrointestinal tract, particularly in the stomach. We describe a case of an enlarging gastric subepithelial lesion (SEL) that was accurately diagnosed and curatively treated by endoscopic full-thickness resection (EFTR). A 50-year-old woman presented with a 10 mm SEL on the posterior wall of the upper gastric curvature. Endoscopic ultrasound (EUS) revealed a low-hypoechoic lesion primarily originating from the third layer with focal, indistinct borders with the muscularis propria. Initial boring biopsy suggested a granular cell tumor based on morphology and SOX10/S100 positivity. Six months later, the lesion had enlarged to 15 mm, and EFTR under general anesthesia with laparoscopic backup was selected to obtain a full-thickness specimen. En bloc resection was successfully achieved, and the defect was completely closed with clips. Histopathological and immunohistochemical examinations revealed biphasic Schwann and perineurial differentiation, confirming a hybrid schwannoma/perineurioma. The postoperative course was uneventful, and no recurrence was observed during the 22-month follow-up. This case highlights the diagnostic value of EFTR for rare neurogenic SELs in which superficial biopsy may be inconclusive.