Features and diagnosis of computed tomography and magnetic resonance imaging on autoimmune pancreatitis

Abstract

Objective To summarize the features of computed tomography (CT) and magnetic resonance imaging (MRI) of autoimmune pancreatitis (AIP) and investigate the key points of diagnosis and identification. Methods The retrospective and descriptive study was conducted. The clinical data of 21 patients with AIP who were admitted to the Affiliated Hospital of Inner Mongolia Medical University between February 2012 and February 2015 were collected. All the patients underwent plain and enhanced scans of CT and MRI, and magnetic resonanced cholangio-pancreatography (MRCP), and then received hormone therapy. Eleven patients with pancreatic cancer and 11 normal subjects who were diagnosed by MRI in the same period were selected, and apparent diffusion coefficient (ADC) was calculated and compared. Observation indicators: (1) situation of imaging examination: ① pancreatic manifestations: density, signal, atrophy, calcification and enlargement of pancreas, change of pancreatic duct, ② manifestations out of pancreas: changes of biliary tract system and kidney, ③ diffusion weighted imaging (DWI) and ADC: comparisons of ADC among AIP, pancreatic cancer and normal pancreas; (2) diagnosis; (3) treatment and follow-up. The follow-up using outpatient examination and telephone interview was performed to detect the clinical symptoms and signs up to February 2016. Measurement data with normal distribution were represented as ±s. Comparisons among groups were done using one-way ANOVA. Pairwise comparison was analyzed by Dunnett′ T3 test. Results (1) Situation of imaging examination: Of 21 patients, 17 received scan of CT and 11 received scan of MRI (7 combined with scan of CT). ① Pancreatic manifestations: 14 patients had diffuse enlargement of pancreas, with full edge and sausage-like change. Plain scan of CT showed uniform isodense shadow, and enhanced scan showed that reduced enhancement in arterial phase and gradually homogenous enhancement in portal vein phase and lag phase with no enhancement in edge of pancreas. Plain scan of MRI showed lesions were manifested as slight hypointensity on T1 weighted imaging (T1WI), slight hyperintensity on T2WI and hyperintensity on DWI. Enhanced scan of MRI showed delayed enhancement, edge of lesions was manifested as slight hypointensity on T1WI and T2WI, without enhancement. Atrophy and calcification of pancreas: 3 patients had atrophy of pancreatic parenchyma in which scattered calcification were seen. Enlargement of pancreas: 4 patients had localized enlargement of pancreas showing false tumor-like change, including 2 with localized enlargement in head of pancreas. Change of pancreatic duct: MRCP showed that diffuse stenosis, local stenosis and local dilatation of pancreatic ducts were respectively detected in 4, 3 and 1 patients. ② Manifestations out of pancreas: 11 patients had changes of biliary tract system, showing intrahepatic bile duct and common bile duct dilation, partial stenosis and extensive bile duct wall thickening. Enhanced scan of MRI showed there was obvious enhancement of bile duct wall. MRCP of 4 patients showed that the beak-like stenosis was seen in the distal common bile duct. Three patients had kidney changes, enhanced scan of CT showed that kidney demonstrated patch-shape hypodense shadow in arterial phase and homogenous enhancement of patch-shape hypodense shadow in lag phase, and plain scan of MRI showed that kidney lesions demonstrated equal signal on T1WI fat suppression (FS) and patch-shape low signal on T2WI FS. Lesions had gradually homogenous enhancement in substance phase and lag phase. ③ DWI and ADC: lesions in patients with AIP and pancreatic cancer demonstrated high signal on DWI (b=1 000 s/mm2) compared with adjacent tissues (no involvement in pancreas or normal pancreatic parenchyma), ADC of pancreas in patients with AIP, with pancreatic cancer and with normal population was (0.001 30±0.000 35)mm2/s, (0.000 80±0.000 14)mm2/s and (0.001 60±0.000 24)mm2/s, respectively, with a statistically significant difference ( F=30.409, P 0.05). (2) Diagnosis: 11 patients were diagnosed by CT examination, with a diagnostic accuracy of 11/17. Eight patients were diagnosed by MRI examination, with a diagnostic accuracy of 8/11. One patient was misdiagnosed as cancer of pancreatic head by CT and MRI examinations, and 1 was misdiagnosed as cancer in the distal common bile duct. (3) Treatment and follow-up: 21 patients underwent regular hormone therapy, and 40 mg prednisolone was given orally a daily for 3-4 weeks and then gradually reduced to 5 mg up to complete relief of the symptoms. All the 21 patients were followed up for 12-45 months. Of 17 patients with abdominal pain and distension, symptoms of 7 patients disappeared and symptoms of 10 patients decreased or occasionally occurred. Of 10 patients associated with jaundice, symptoms of 7 and 2 patients disappeared and decreased, respectively, and symptoms of 1 patient subsided. Conclusion CT and MRI examinations of pancreas demonstrate sausage-like and false tumor -like changes, the non-neoplastic bile and pancreatic duct stenosis combined with IgG4 related diseases in other organs is an important imaging evidence for diagnosis and differential diagnosis of AIP. Key words: Autoimmune pancreatitis; Tomograghy, X-ray computed; Magnetic resonance imaging; Diagnosis