Gastritis Cystica Profunda With High-Grade Dysplasia Mimicking Gastrointestinal Stromal Tumor: A Histopathological Pitfall in the Assessment of Submucosal Invasion.

Background: Gastritis cystica profunda (GCP) is an uncommon gastric lesion characterized by displacement of cystically dilated glands into the submucosa. It may present as a submucosal mass mimicking gastrointestinal stromal tumor (GIST). The coexistence of GCP with high-grade dysplasia is extremely uncommon and may pose a significant diagnostic challenge by simulating invasive carcinoma. Case Presentation: We report a case of a 54-year-old patient whose endoscopic and radiographic features suggested a GIST in the gastric cardia. Surgical resection was performed. Histopathological examination revealed cystically dilated glands extending into the submucosa, lined by high-grade dysplastic epithelium. Importantly, the muscularis mucosae was focally disrupted, and the submucosal component comprised both dysplastic and nondysplastic glands displaced together within smooth muscle bundles derived from the muscularis mucosae and accompanied by lamina propria-type stroma, supporting mucosal prolapse rather than true invasion. A final diagnosis of high-grade dysplasia arising in GCP was established. Conclusion: This case highlights an important diagnostic pitfall in distinguishing pseudoinvasion from true invasive carcinoma in submucosal gastric lesions. Recognition of this entity and careful assessment of the muscularis mucosae together with the character of the displaced glands are essential to avoid overstaging and unnecessary aggressive management.