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

## TL;DR

A rare hybrid nerve sheath tumor in the stomach was successfully diagnosed and treated using endoscopic full-thickness resection.

## Contribution

This case report demonstrates the effectiveness of EFTR in diagnosing and treating a rare gastric neurogenic tumor.

## Key findings

- EFTR provided a full-thickness specimen that enabled accurate histopathological diagnosis of a hybrid schwannoma/perineurioma.
- The patient had no recurrence after 22 months of follow-up following successful en bloc resection.
- Endoscopic ultrasound and EFTR proved valuable in managing a neurogenic subepithelial lesion with inconclusive biopsy results.

## Abstract

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.