Focal Pancreatitis

At times acute pancreatitis involves only a portion of the pancreas, with such focal pancreatitis then evolving into chronic changes limited to a segment of the pancreas. A separate description here of focal pancreatitis is not meant to imply that it is a separate disease entity; rather, its importance lies in its mimicry of pancreatic cancer. An annular pancreas, with pancreatitis limited to the annular portion, has already been discussed. Some descending duodenal stenoses are secondary to focal pancreatitis in the annular segment. A history of acute or chronic pancreatitis is often lacking in those with focal pancreatitis. Most often focal pancreatitis involves the pancreatic head. Computed tomography shows focal pancreatitis to be hypodense and US reveals hypoechoic tumors. It tends to be hypervascular at angiography.
Groove Pancreatitis One form of segmental chronic pancreatitis is called “groove pancreatitis.” The groove is located between the pancreatic head, the duodenum, and the common bile duct. Why focal pancreatitis should develop preferentially in this location is puzzling, although this region of the pancreas is drained by the duct of Santorini, and obstruction of this duct or aberrant ducts may play a role. Relation of this entity to focal annular pancreatitis is conjecture. A typical appearance is a tumor simulating a pancreatic head carcinoma; differentiation between the two entities is difficult at best, and some of these patients undergo resection. Some develop a duodenal stricture. Magnetic resonance imaging in five patients revealed a sheet-like tumor between the pancreatic head and duodenum; these tumors were hypointense relative to the pancreas on T1- and iso- to slightly hyperintense on T2-weighted images and had delayed contrast enhancement. Histology revealed fibrosis.
Inflammatory Pseudotumor
A number of pancreatic inflammatory pseudotumors have been described. Whether these should be considered a type of focal pancreatitis or as a separate entity is not clear. Computed tomography detects an inflammatory pseudotumor of the pancreas simply as a large tumor; histology shows a mixed infiltrate of spindle cells, lymphocytes, histiocytes, and plasma cells.
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