It’s not a GIST: A Histopathological Investigation of a Rare Gastric Schwannoma

Background: Gastric schwannomas are rare gastrointestinal mesenchymal tumors, accounting for <0.2% of all gastric neoplasms. Gastric schwannomas are benign, arise from the gastrointestinal nerve plexus, and are often misdiagnosed as gastrointestinal stromal tumors (GISTs). Gastric schwannomas are typically incidental findings on conventional imaging studies, surgery, or autopsy. Reported patients are usually asymptomatic. Gastric schwannomas can be differentiated from GIST and other mesenchymal gastrointestinal tumors through the use of immuno-histochemical markers such as S100, Vimentin, and glial fibrillary acidic protein (GFAP).

Case Information: During routine dissection of a 78-year-old female, a 1.5 x 1.2 x 1.0 cm tan, firm nodule protruding from the anterior stomach wall was identified. The nodule was located 11 cm from the gastroesophageal junction, 7 cm from the incisura angularis, and 6 cm from the pyloric sphincter. Sectioning revealed white, whorled, and rubbery cut surfaces. No hemorrhage, necrosis, or cystic spaces were grossly appreciated. Subsequently, the tissue underwent routine fixation, processing, paraffin embedding, sectioning, and hematoxylin and eosin (H&E) staining. Using light microscopy, histopathologic findings included a well-circumscribed area containing mostly eosinophilic spindle cells with nuclear palisading, foci of lymphoid infiltration,and a micro-trabecular pattern noted centrally. Additionally, a peripheral lymphoid cuff was present. No mitotic figures were identified. Based on our histopathology findings, we hypothesized the presented nodule to be a gastric schwannoma. This diagnosis was corroborated by immunohistochemistry to demonstrate positive S100b protein expression. Common differential diagnoses include gastrointestinal stromal tumors (GISTs), leiomyomas, and solitary fibrous tumors, all of which lack S100 protein reactivity.

Conclusion: This case aims to contribute an additional report about gastric schwannomas to better enhance our collective understanding of this rare lesion.