Triangular with sharp, linear margin between normal pancreas and area of fatty infiltration
• Lack of mass effect or dilatation of common bile duct or pancreatic duct
• Pancreas maintains normal external contour and normal pancreatic lobulations
• Chemical shift MR (in- and out-of-phase imaging) most specific modality for making a definitive diagnosis in confusing cases
Signal dropout in areas of fatty infiltration on opposed-phase images
TOP DIFFERENTIAL DIAGNOSES
• Pancreatic head adenocarcinoma
• Focal pancreatitis
• Diffuse fatty replacement of pancreas
• Intrapancreatic lipoma
PATHOLOGY
• Dorsal pancreatic bud develops into body, tail, and anterior head of pancreas, while ventral bud develops into posterior head and uncinate process
• Fat accumulates preferentially within anterior head of pancreas derived from dorsal foregut bud
• May reflect more tightly packed pancreatic lobules in ventral bud compared to dorsal bud
CLINICAL ISSUES
• Incidental finding in asymptomatic patients
• No association with endocrine or exocrine abnormalities
(Left) Axial arterial phase CECT demonstrates a low-attenuation area anteriorly within the head of the pancreas. Note the normally enhancing uncinate process posterior to this area, as well as the sharp linear boundary demarcating the low attenuation area.
(Right) A coronal curved planar reformation along the pancreatic duct demonstrates a normal duct. The characteristic location and the lack of mass effect on the duct are key findings to suggest the diagnosis of focal fatty infiltration.
(Left) Axial in-phase GRE MR image demonstrates uniform signal in the head of the pancreas . (Courtesy H. Harvin, MD.)
(Right) Axial opposed-phase MR in the same patient shows dropout of signal in the anterior aspect of the head, a classic finding confirming asymmetric fatty lobulation. Note the preserved higher signal and lack of dropout from the normal pancreatic tissue in the uncinate process . (Courtesy H. Harvin, MD.)
TERMINOLOGY
Abbreviations
•
Synonyms
• Focal lipomatosis or focal fatty infiltration of pancreas
Definitions
• Focal accumulation of fat within anterior aspect of head of pancreas, a normal variant that may simulate a hypodense mass on CT
IMAGING
General Features
• Best diagnostic clue
Ill-defined, low-attenuation area (without mass effect or ductal dilatation) in anterior head of pancreas
• Location
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anteriorly within the head of the pancreas. Note the normally enhancing uncinate process 
posterior to this area, as well as the sharp linear boundary demarcating the low attenuation area.
demonstrates a normal duct. The characteristic location and the lack of mass effect on the duct are key findings to suggest the diagnosis of focal fatty infiltration.
. (Courtesy H. Harvin, MD.)
in the anterior aspect of the head, a classic finding confirming asymmetric fatty lobulation. Note the preserved higher signal and lack of dropout from the normal pancreatic tissue in the uncinate process 
. (Courtesy H. Harvin, MD.)
