The retroperitoneum space comprises anterior pararenal space, perirenal space and posterior pararenal space. Pancreas is a retroperitoneal organ and located in the anterior pararenal space of the retroperitoneum. Left and right sides anterior pararenal space are potentially communicated, which contains many adipose tissues and a little connective tissues. The exacerbation of acute pancreatitis results in the lesion spreading into adjacent area of pancreas in the retroperitoneal space. In addition, the lesion could spread into bare area of stomach, posterior colonic region, subperitoneal space and pelvic retroperitoneal space through the same anatomical space or communicating space. Due to the fascia destruction by pancreatic enzymes or the lesion directly diffuse through the weak fascia, the lesion could also diffuse across fascia to perirenal space, posterior pararenal space, the peritoneal cavity and abdominal wall. Finally, a series of complications are developed. The diffusion paths of acute pancreatitis are complex and diverse. Familiarity with these diffusion paths is useful for determining the severity and guiding therapy.

Pancreatitis; Retroperitoneal space; Inflammation; Diffusion