Retroperitoneal Bronchogenic Cyst Mimicking a Pancreatic Cystic Lesion with Extremely High Level of Intralesional Fluid CA-19.9 Antigen: Benign in Disguise

Bronchogenic cysts are congenital benign tumors resulting from abnormal budding of the primitive foregut. Usually presented on the posterior mediastinum, its presence on the retroperitoneum is extremely rare. We present an asymptomatic lady patient with a retroperitoneal cystic lesion that was submitted to endoscopic ultrasound–guided biopsies and intracystic fluid aspiration with histology excluding malignance despite intracystic fluid biochemical analysis that disclosed extremely high carbohydrate antigen 19–9. Definite diagnosis of bronchogenic cyst was only possible after complete surgical resection of the lesion. Furthermore, we discuss the use of this antigen as a tumor marker in this situation and its relevance to the preoperative diagnosis of such lesions.