Case Report: A rare case of gastric cardia bronchogenic cyst: diagnostic challenges and EUS findings with elevated cyst-fluid tumor markers.

Bronchogenic cysts are rare congenital foregut malformations that most commonly occur in the thoracic cavity, whereas involvement of the gastric cardia is exceptionally uncommon. We report the case of a 36-year-old man who presented with abdominal distension and was found to have a cystic lesion adjacent to the gastric cardia. Contrast-enhanced computed tomography and magnetic resonance imaging demonstrated a well-circumscribed, non-enhancing cystic mass, but the exact origin and nature of the lesion remained uncertain. Endoscopic ultrasound showed a 4.5 × 5.0 cm homogeneous hypoechoic lesion arising from the muscularis propria layer of the gastric cardia. Endoscopic ultrasound-guided fine-needle aspiration yielded dark-brown, turbid cyst fluid, and cyst-fluid analysis showed a neutrophil-predominant, exudative profile with markedly elevated tumor-associated markers, including CEA, CA19-9, CA125, and CYFRA 21-1. Microbiological smear and culture examinations for bacteria, fungi, and mycobacteria were negative. Given the patient's symptoms, lesion size, uncertain diagnosis, abnormal cyst-fluid profile, and inability to exclude a cystic neoplasm preoperatively, laparoscopic cyst excision with gastric wall repair was performed. Histopathological examination confirmed the diagnosis of a bronchogenic cyst, characterized by pseudostratified ciliated columnar epithelium and smooth muscle within the cyst wall. The patient recovered uneventfully, and no recurrence was observed during 1 year of follow-up. This case highlights the diagnostic challenges of gastric bronchogenic cysts and the complementary role of endoscopic ultrasound in localizing and characterizing subepithelial cystic lesions. Elevated cyst-fluid tumor markers should be interpreted cautiously and should not be regarded as evidence of malignancy in isolation, as their diagnostic and prognostic significance in gastric bronchogenic cysts remains uncertain.