Could It Be Autoimmune Pancreatitis? MDCT May Miss Important Signs
In an article published in the July issue of AJR, researchers have found that while MDCT accurately differentiates autoimmune pancreatitis from pancreatic ductal adenocarcinoma and acute interstitial pancreatitis, autoimmune pancreatitis should not be ruled out by MDCT alone.
Coauthor Stephanie Lee-Felker of the David Geffen School of Medicine at UCLA talked with InBrief about the findings.
Why is it so challenging to definitively diagnose autoimmune pancreatic disease?
Autoimmune pancreatitis is a heterogeneous disease, presenting with various clinical symptoms, laboratory alterations, and imaging findings that can overlap with other disease processes, including pancreatic ductal adenocarcinoma and acute interstitial pancreatitis.
How effective is MDCT in differentiating between pancreatic disorders?
When classic imaging features are present, MDCT differentiates autoimmune pancreatitis, pancreatic ductal adenocarcinoma, and acute interstitial pancreatitis with high accuracy. In our study, presence of sausage shape and low attenuation halo with absence of pancreatic duct and biliary dilatation differentiated autoimmune pancreatitis from pancreatic ductal adenocarcinoma with an accuracy of 88%. Likewise, presence of sausage shape and absence of peripancreatic stranding differentiated autoimmune pancreatitis from acute interstitial pancreatitis with an accuracy of 82%.
However, the presence of atypical imaging features diminishes the diagnostic accuracy of MDCT. In these cases, correlation with clinical information, such as serum analyses and biopsy results, is helpful for accurate diagnosis.
The study finds that some atypical imaging features often used to rule out autoimmune pancreatitis (as opposed to malignancy) should not be considered definitive. What are they, and why?
In our series, there was no significant difference in the incidence of focal pancreatic involvement, vascular involvement, or peripancreatic lymphadenopathy between autoimmune pancreatitis and pancreatic ductal adenocarcinoma, even though these imaging features are usually considered to be pathognomonic for malignancy.
There are specific challenges associated with differentiating between autoimmune pancreatic disease and pancreatic ductal adenocarcinoma. What should the radiologist be looking for?
Start by deciding whether the distribution of pancreatic involvement is diffuse or focal—the latter is more problematic for accurate diagnosis. For focal pancreatic processes, the differential diagnosis should include autoimmune pancreatitis and acute interstitial pancreatitis in addition to pancreatic ductal adenocarcinoma, even in the presence of vascular involvement and peripancreatic lymphadenopathy.
Then, look for other associated findings. The presence of a low attenuation halo and extrapancreatic findings, such as biliary wall enhancement and characteristic solid renal lesions, favors focal autoimmune pancreatitis. The presence of pancreatic dilatation and biliary dilatation favors pancreatic ductal adenocarcinoma, and the presence of peripancreatic stranding favors acute interstitial pancreatitis.
What was the key conclusion of the study?
For focal pancreatic processes, always consider—and raise the possibility of—autoimmune pancreatitis. The radiologist can play an important role in prompting further diagnostic workup for accurate diagnosis by suggesting correlation with serum immunoglobulin 4 level and tissue sampling, potentially preventing unnecessary surgery.