Experimental Study Of Chronic Pancreatitis And MRI In Differentiation Between Clinic Mass-Forming Focal Chronic Pancreatitis And Pancreatic Carcinoma

ObjectiveTo establish an animal model of cat with chronic pancreatitis, and to examine the imaging and pathological features of normal pancreas and chronic pancreatitis of cats.To discuss the diagnostic value in Mass-Forming Focal Chronic Pancreatitis (FCP) and Pancreatic carcinoma (PC) with magnetic resonance cholangiopancreatography (MRCP), multi-phasic dynamic contrast enhancement MRI (DCE-MRI) and diffusion weighted imaging (DWI).Methods1. Thirty-two cats were included in this study. Eight healthy cats served as control. An upper midline laparotomy was performed to partially ligate the pancreatic duct to produce chronic pancreatitis in twenty-four cats (CP group,3 weeks,5 weeks,7 weeks after establishing model). All cats underwent MRI plain scanning, MRCP scaning and histopathological examination.2.2D/3D MRCP findings in 30 clinic cases of pancreatic carcinoma and 30 clinic cases of Mass-Forming Focal chronic Pancreatitis which proven by histopathology and or clinical follow-up were retrospectively analyzed.3. All cases underwent five phases DCE-MRI were divided into three groups, pancreatic carcinoma (n=28) confirmed by pathology, mass-forming focal chronic pancreatitis (n=15) confirmed by pathology or clinical diagnosis, and normal pancreas (n=20). The signal intensity of ROI (region of interest) was measured at the pancreas on all five phases, and for each, the enhanced rate was calculated, meanwhile, time-signal intensity curves(TIC) of the mass and the remaining pancreas were obtained in all 3 groups. Then the patterns of the TICs were classified into 5 types according to the time of a peak (18s,45s,75s,2.5min,4min after bolus injection of contrast material), namely, type-Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅴ, respectively. Then, according to the profile of the tail of TIC, the type of the masses were classified into two subtypes, subtype-a (slow decline) and subtype-b (plateau).4. All cases underwent diffusion weighted imaging (DWI)(b=200,400,600s/mm2) were divided into three groups, pancreatic carcinoma (n=28) confirmed by pathology, mass-forming focal chronic pancreatitis (n=15) confirmed by pathology or clinical diagnosis, and normal pancreas (n=20). DWI maps were obtained. ADC values of the masses and the remaining pancreas of FCP and PC, and the normal pancreas were measured.Results1. Five cats were sacrificed after duct ligation in the CP group. In the left 19 cats,4 cats had normal pancreas and 15 piglets had chronic obstructive pancreatitis, including 7 cats with grade 1,5 cats with grade 2, and 3 cats with chronic pancreatitis grade 3. The successful rate of CP induction was 62.5% in the cats. The normal pancreas and chronic pancreatitis of cats were much the same as the ones of the human with respect to anatomic location, general morphology, MRI imaging features.2. MRCP characteristics in FCP group included:(1)irregular dilatation of the pancreatic duct across the whole segment of the lesion(n=13,43.3%), stones within the pancreatic duct(n=6,20%), (2)tapering of the dilated bile duct in the region of pancreatic head(n=8,26.7%), (3)"double tubes sign"(n=6,20%). MRCP characteristics in PC group included:(1)abrupt interruption of the continuously dilated the pancreatic duct at the site of the tumor and the lumen looking smooth(n=17,56.7%), (2)abrupt interruption of the dilated common bile duct at site of the tumor(n=15,50.0%), (3) "double tubes sign"(n=14, 46.7%).3. All normal pancreases have demonstrated TIC type-I, Type-Ⅳb and type-ⅤTIC were only recognized in PC (P=0.036, P=0.008), but type-Ⅰa and type-Ⅱa only in FCP (P=0.037, P=0.000). Furthermore, type-ⅠTIC in the remaining pancreas was recognized more in PC than FCP (P=0.027). Besides, in the arterial phase, enhanced rate in PC is lower than in FCP (P=0.031).4. On b= 600s/mm2 DWI, FCP was visually indistinguishable from the remaining pancreas whereas PC was hyperintense relative to the remaining pancreas. The mean ADC value of PC{(1.1918±0.2635)×10-3}was lower than the remaining pancreas {(1.4139±0.2179)×10-3, P=0.001}, FCP{(1.3650±0.2585)×10-3, P=0.038)}, and pancreatic gland in the normal pancreas{(1.5221±0.2239)×10-3, P=0.000}. There was no significant difference of ADC values between the mass and the remaining pancreas of FCP{(1.5362±0.2217)×10-3, P=0.07}, and pancreatic gland in the normal pancreas (P=0.059). ConclusionChronic obstructive pancreatitis can be produced by partial ligation of the pancreatic duct in cats, and the pancreas of cats is fit for MRI imageologic study of chronic pancreatitis.MRCP characteristics of pancreatobiliary duct dilation are of great significance in differential diagnosis of FCP and PC. Differences on quantitative analysis of multi-phasic DCE-MRI and DWI may help to differentiate clinic PC, FCP and normal pancreas from each other.