Gastric accessory spleen mimicking gastrointestinal stromal tumor: a case report and literature review

Background: Accessory spleens occur in approximately 10–30% of the general population, but intramural implantation in the gastric wall is exceedingly rare, with fewer than 60 cases documented in the English-language literature to date. These lesions pose a significant diagnostic challenge because their endoscopic ultrasonographic appearance closely resembles gastrointestinal stromal tumors (GISTs) and other submucosal tumors (SMTs), potentially leading to unnecessary operative intervention in the absence of tissue-level diagnosis. Case presentation: A 49-year-old female presented with a 3-month history of epigastric pain, postprandial fullness, early satiety, and nausea. Esophagogastroduodenoscopy demonstrated a well-defined submucosal gastric lesion. Endoscopic ultrasonography (EUS) revealed a homogeneous hypoechoic lesion with smooth margins arising from the fourth EUS layer (muscularis propria), raising a primary suspicion of GIST. EUS-guided fine-needle biopsy (EUS-FNB) was subsequently performed; histopathological analysis demonstrated normal splenic tissue, including red pulp, white pulp, and vascular sinusoids. Immunohistochemical staining confirmed strong CD8 positivity in littoral cells lining the sinusoidal walls, establishing the definitive diagnosis of intramural gastric accessory spleen (IGAS). Staining for c-KIT (CD117) and DOG1 was negative, excluding GIST. Following a multidisciplinary discussion, the patient elected conservative management. She remained clinically stable during follow-up. Conclusion: IGAS is a rare but clinically important differential diagnosis of gastric SMTs. EUS-FNB combined with immunohistochemical identification of CD8-positive littoral cells is a safe and highly effective, minimally invasive strategy that provides a pathognomonic tissue diagnosis. When the diagnosis is conclusively established, conservative management with endoscopic surveillance is appropriate and spares the patient the morbidity of unnecessary operative intervention.