The retroperitoneum (RP) is an anatomical space located behind the abdominal or peritoneal cavity. Abdominal organs that are not suspended by the mesentery and lie between the abdominal wall and parietal peritoneum are said to lie within the RP (kidneys, adrenal glands, pancreas, and parts of the aorta, inferior vena cava, duodenum, and colon). Several individual spaces make up the RP. These spaces are the anterior pararenal space, posterior pararenal space, and the perirenal space (1). Methods for retroperitoneal biopsy include open/laparoscopic surgery, or CT-guided biopsy. We present using of EUS-FNA/FNB trought the duodenum as a new route for accessing the retroperitoneum

We present diagnostic procedure in patient with abdominal pain,diabetes mellitus, weight loosing, and excessive consumption of alcohol. MSCT scan show retroperitoneal mass (RPM) dorsal to the pancreas, which has been pushed ventrally, and partly with infiltration of the head and the initial part of the body of the pancreas, a large expansive infiltrative formation  (AP × LL × CC - 51 × 81 × 71 mm). The formation was heterogeneous with cystic lesions, some of which contain calcifications.Transduodenal endoscopic ultrasound (FujiFilm Arietta 850) -guided fine-needle biopsy (EUS-FNB – 22 ga) was second step. Patohystological finding show a regular pancreatic glands and pieces of squamous epithelium without malignant tissue.

After consultation with the multidisciplinary team, surgery was performed as follows - pancreatodudenotomy sec Whipple, pancreatojejunostomy, hepaticojejunostomy, GEA, EEA sec. Roux, cholecystectomy, VAC drainage. Patohystological finding show a regular and irregular pancreatic glands without malignant tissue – conclusion - changes caused by recurrent chronic pancreatitis of ethylic etiology.

Transduodenal endoscopic ultrasound FNA/FNB for diagnosis of RPM is still only sporadically mentioned in the literature. But this is a powerful diagnostic tool in the hands of an experienced endoscopist.