Segmental pancreatitis is not a distinct entity in itself, but describes an imaging differential.
With segmental pancreatitis, a patient presents with clinical pancreatitis (signs, symptoms, laboratory markers), but on imaging, only a portion of the gland appears to have changes related to pancreatitis. It is not uncommon for part of the pancreas to be disproportionally affected in acute pancreatitis, but with segmental pancreatitis, parts of the gland are normal-appearing on imaging. The imaging differential varies depending on whether the involved segment is the head of the pancreas or the tail.
Head of pancreas
Tail of pancreas
The most important thing to assess is whether a mass in the pancreas (such as pancreatic adenocarcinoma) is obstructing the duct and causing obstructive pancreatitis in the upstream gland. Similarly, a stone obstructing the pancreatic duct could cause upstream pancreatitis in the tail. Once these are excluded, other possibilities can be considered, such as