Female, 54 years old, with intermittent back pain for 1 month, aggravated for 2 days, was found to have a “large retroperitoneal occupancy” on CT. Imaging findings (above): An irregular mass with a size of 167.5px×312.5px×252.5px was seen in the caudal part of the pancreatic body, with clear borders and circular calcifications of varying thicknesses at the edges, with heterogeneous internal density and soft tissue density in the main body. The head and neck of the pancreas had uniform density and no abnormal foci of enhancement were seen. Preoperative imaging impression: teratoma? malformation tumor? CT-guided puncture biopsy (above): the puncture tissue was yellow mucous liquid material, unshaped, and 10 ml of yellow mucous necrotic material was withdrawn by syringe. The puncture pathology results suggested that the degenerated necrotic material was sent for examination, and no viable cellular component was seen. Postoperative pathology: collagenized fibrous cystic wall tissue with significant calcification was sent for examination, with a large amount of necrotic material attached to the inner wall, and no viable components were seen. The possibility of chronic necrotizing pancreatitis was considered to be high, based on a combination of pathology and clinical findings. Regarding the puncture biopsy of pancreatic lesions: pancreatic puncture biopsy carries the risk of pancreatic fistula secondary to peritonitis, and the selection of indications for puncture biopsy is particularly strict compared with other sites. In this case, the preoperative CT showed that the normal pancreatic tissue in the caudal part of the pancreatic body disappeared and was replaced by an irregular soft tissue density lesion with circumferential calcification visible at the edges, and there was no risk of pancreatic fistula when the lesion was removed from the caudal part of the body through the tail of the pancreas. In this case, the preoperative CT lesion was not only calcified at the margins, but also had a dotted piece of calcification within the lesion, and a strip of fatty tissue was visible within the lesion, so the possibility of teratoma or malformation tumor was considered preoperatively. The preoperative puncture and postoperative pathology suggested that the lesion was degenerated necrotic material and no viable cellular component was seen, so the possibility of necrotizing pancreatitis was considered, and the possibility of intra-abdominal adipose tissue involvement was considered.