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Diffusion-weighted magnetic resonance imaging is useful in differentiating autoimmune pancreatitis (AIP) from pancreatic cancer and in gauging the efficacy of steroid therapy for pancreatitis, the results of a Japanese study suggest.

"As AIP patients often present with painless jaundice in the setting of a pancreatic mass, they are sometimes misdiagnosed as having pancreatic cancer and undergo pancreatic resection," researchers note in the March 9th online issue of The American Journal of Gastroenterology.

The article says that roughly 2.5% of all pancreatoduodenectomies in North America are due to a mistaken pancreatic cancer diagnosis in patients with AIP.

Diffusion-weighted MRI evaluates the rate of microscopic water droplet diffusion within tissues, yielding a quantitative measurement called the apparent diffusion coefficient. In general, malignant tumors have higher cellularity and thus higher apparent diffusion coefficients than benign lesions.

Hypothesizing that diffusion-weighted MRI techniques could help diagnose AIP, Dr. Terumi Kamisawa, of Tokyo Metropolitan Komagome Hospital, and colleagues compared the imaging studies of 13 AIP patients (13 imaging studies before steroid therapy, six after) and 40 pancreatic cancer patients.

All of the cancer patients had solitary segmental high intensity areas. By comparison, 6 of the AIP had solitary segmental high intensity areas, 4 had diffuse high-intensity areas, and 3 had multiple segmental areas.

The shape of the high intensity areas was also different: pancreatic cancer patients had nodular-shaped areas more frequently, while AIP patients had longitudinal shapes (p = 0.005). Finally, the apparent diffusion coefficient was significantly lower in AIP than in cancer patients. Moreover, apparent diffusion coefficient values decreased markedly after steroid therapy for AIP.

"As AIP can mimic pancreatic cancer clinically and radiologically, it is of utmost importance to differentiate between those two diseases," the investigators wrote. They recommend a prospective study, using apparent diffusion coefficient cutoff values established in the present study, to evaluate the clinical utility of diffusion-weighted MRI in differentiating AIP from pancreatic cancer.

Source: ACR

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