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Signs for Differentiating Autoimmune Pancreatitis versus Pancreatic Cancer

February 25, 2008
Written by: , Filed in: Gastrointestinal Imaging
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The objective of a recent study was to determine if there are findings on dual-phase CT that can help one differentiate between autoimmune pancreatitis and pancreatic carcinoma.

The study has concluded that helpful findings on dual-phase CT that favor a diagnosis of autoimmune pancreatitis include diffusely decreased enhancement of the pancreas, a capsule-like soft tissue rim, bile duct enhancement, and renal involvement.

Participants/Methodology
This retrospective analysis was comprised of 22 men and 3 women who had been diagnosed with autoimmune pancreatitis and had undergone dual-phase CT at the time of presentation. The control groups consisted of patients with pancreatic carcinoma and patients with a normal pancreas who had undergone dual-phase CT of the pancreas. Dual-phase pancreatic CT protocol contrast scan delays ranged between 35 to 45 seconds and 60 to 70 seconds.

Three radiologists reviewed the CT images. The pancreas was divided into segments (head, body, and tail) and each was categorized on the basis of size and enhancement. Size was categorized as normal, enlarged, or atrophied, and the enhancement as normal or decreased in both pancreatic and hepatic phases. When a low-attenuation mass was present, the attenuation of the mass was used as the attenuation of that segment.

Other findings that were included in the evaluation were pseudocysts, pancreatic calcifications, peripancreatic fat stranding, and a capsule-like rim of soft tissue. The pancreatic duct was evaluated for dilatation and abrupt cutoff, and vascular involvement was also evaluated. The common bile duct was evaluated for the presence of dilatation, stent, or circumferential wall enhancement.

Other previously described findings associated with autoimmune pancreatitis, such as retroperitoneal fibrosis and solid renal lesions were also considered.

Review for Practicing Radiologists The University of California, San Francisco School of Medicine, Department of Radiology and Biomedical Imaging Review for Practicing Radiologists an intensive clinical radiologic review and self-assessment covering the following radiology subspecialties: Vascular-Interventional, Breast, Neuro, Gastrointestinal and Pulmonary Imaging. The program is designed for radiologists in clinical practice. Click here to read more or order: Review for Practicing Radiologists

Results of the Study
The following findings were significantly more frequently seen in patients with autoimmune pancreatitis: diffuse decreased enhancement; capsule-like rim of soft tissue; peri-pancreatic fat stranding; pancreatic calcification; common bile duct wall enhancement; and solid renal lesions.

A capsule-like rim of soft tissue was present in 40%, peripancreatic fat stranding in 60%, bile duct wall enhancement in 52%, and renal involvement in 28% of patients with autoimmune pancreatitis.

Renal involvement manifested as small peripheral cortical nodules, round or wedge-shaped lesions, or as diffuse patchy involvement. A dilated pancreatic duct with abrupt cut off was more frequently seen in patients with carcinoma.

Reviewer’s Comments
These results are useful in that they demonstrate a few helpful signs that can aid in differentiating between autoimmune pancreatitis and pancreatic carcinoma. These signs are helpful when the entire gland is involved.

However, as shown in this study, autoimmune pancreatitis would still prove to be a diagnostic imaging dilemma when confronted with a low-attenuation mass, focal enlarged pancreas, or biliary dilatation without a discrete mass. One limitation of this study is its retrospective nature.

Author: John C. Sabatino, MD

Reference
Takahashi N, Fletcher JG, et al. Dual-Phase CT of Autoimmune Pancreatitis: A Multireader Study.
AJR;
2008; 190 (February): 280-286:

Review for Practicing Radiologists The University of California, San Francisco School of Medicine, Department of Radiology and Biomedical Imaging Review for Practicing Radiologists an intensive clinical radiologic review and self-assessment covering the following radiology subspecialties: Vascular-Interventional, Breast, Neuro, Gastrointestinal and Pulmonary Imaging. The program is designed for radiologists in clinical practice. Click here to read more or order: Review for Practicing Radiologists
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