Retroperitoneal pseudocyst dissecting into the pleural space
The retroperitoneal pseudocyst is particularly difficult to see on the CT, however, there is the suggestion of some degree of inflammation tracking up from the pancreas evidence by retroperitoneal stranding, esophageal wall thickening/hazy surrounding soft tissue, and left pleural effusion.
On the MRI, a thin, serpentine enhancing tract of fluid can be seen extending from the pancreatic tail through the diaphragm and into the left pleural space, resulting in pleural effusion and pleural enhancement. In particular, the T2 fat sat and postcontrast sequences show the pseudocyst most effectively. This inflammatory pleural effusion is likely responsible for the patient's persistent left upper quadrant pain. There is also a small, chronic gastric subserosal pseudocyst along the posterior body.
Pseudocysts are most commonly thought of as surrounding the pancreas. However, over time they can track basically anywhere along the path of least resistance: Inferiorly into the pelvis or superiorly into the mediastinum and even into the neck.