自身免疫性胰腺炎CT及MRI影像学特征与诊断

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

目的：总结自身免疫性胰腺炎（AIP）的CT及MRI影像学特征，探讨其诊断与鉴别诊断要点。 方法：采用回顾性描述性研究方法。收集2012年2月至2015年2月内蒙古医科大学附属医院收治的21例AIP患者的临床资料。患者行CT平扫及增强扫描、MRI平扫及增强扫描、MRCP检查，完善检查后行激素治疗。选取同一时期行MRI检查并确诊的胰腺癌及正常胰腺受试者各11例，分别测量其表观弥散系数（ADC）值进行比较。观察指标：（1）影像学检查情况：①胰腺表现：胰腺密度和信号，胰腺萎缩和钙化，胰腺增大，胰管改变。②胰腺外表现：胆道系统及肾脏改变。③弥散加权成像（DWI）及ADC值：比较AIP、胰腺癌和正常胰腺ADC值。（2）诊断情况。（3）治疗及随访情况。采用门诊及电话随访，随访内容为患者的临床症状及体征，随访时间截至2016年2月。正态分布的计量资料以±s表示，多组间比较采用单因素方差分析。两两比较采用Dunnett′ T3法检验。 结果：（1）影像学检查情况：21例患者中，17例行CT检查，11例行MRI检查（其中7例联合行CT检查）。①胰腺表现：胰腺密度和信号MRI检查示胰腺弥漫性增大14例，边缘饱满，呈“腊肠样”改变。CT平扫呈均匀等密度影，增强扫描动脉期强化程度减低，门静脉期及延迟期逐渐均匀强化，边缘未见强化。MRI平扫病灶T1加权成像呈稍低信号，T2加权成像呈稍高信号，DWI呈高信号，增强扫描呈延迟强化；病灶边缘T1、T2加权成像均呈稍低信号，增强未见强化。胰腺萎缩和钙化：3例胰腺实质萎缩，内见散在钙化。胰腺增大：4例胰腺局限性增大呈“假肿瘤样”改变，其中胰头部局限性增大2例。胰管改变：MRCP检查示4例表现为胰管弥漫性狭窄，3例表现为局限性狭窄，1例局限性扩张。②胰腺外表现：MRCP检查示11例患者表现为胆道系统改变，可见肝内胆管及胆总管扩张，部分狭窄，胆管壁广泛增厚，MRI增强扫描检查示胆管壁呈明显强化。4例患者行MRCP检查可见胆总管末段呈“鸟嘴样”狭窄。3例患者表现为肾脏改变，CT增强扫描检查动脉期可见肾脏斑片状低密度影，延迟期斑片状低密度影均匀强化，MRI平扫T1抑脂序列图像示肾脏病灶呈等信号，T2抑脂序列图像呈斑片状低信号。实质期及延迟期病灶逐渐均匀强化。③DWI及ADC值：AIP患者及胰腺癌患者DWI（b=1 000 s/mm2）示病灶相对于邻近组织（未受累的胰腺或正常胰腺实质）呈高信号，AIP患者、胰腺癌患者、正常人群胰腺ADC值分别为（0.001 30±0.000 35）mm2/s、（0.000 80±0.000 14）mm2/s、（0.001 60±0.000 24）mm2/s，3者比较，差异有统计学意义（F=30.409，P〈0.05）。胰腺癌患者分别与AIP患者和正常人群比较，胰腺ADC值差异均有统计学意义（P〈0.05），AIP患者与正常人群比较，差异无统计学意义（P〉0.05）。（2）诊断情况：CT检查确诊11例，诊断准确率为11/17。MRI检查确诊8例，诊断准确率为8/11。1例患者CT及MRI检查均误诊为胰头癌，1例MRI检查误诊为胆总管下段癌。（3）治疗及随访情况：21例患者常规接受激素治疗，每日口服泼尼松龙40 mg，持续3～4周后逐步减量，每周5 mg，直至症状完全缓解。21例患者全部获得随访，随访时间为12～45个月。17例腹痛、腹胀患者中，7例症状消失，10例症状减轻偶尔发作；10例伴有黄疸的患者中，7例黄疸消失，2例减轻，1例消退。 结论：胰腺CT和MRI影像学检查表现为“腊肠样”“假肿瘤样”改变，非肿瘤性胆胰管狭窄，合并其他器官的IgG4相关疾病是诊断和鉴别诊断AIP的重要影像学依据。

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 cholangiopancreatography （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 followup. The followup 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 oneway 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 ＂sausagelike＂ 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 tumorlike＂ 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 beaklike stenosis was seen in the distal common bile duct. Three patients had kidney changes, enhanced scan of CT showed that kidney demonstrated patchshape hypodense shadow in arterial phase and homogenous enhancement of patchshape hypodense shadow in lag phase, and plain scan of MRI showed that kidney lesions demonstrated equal signal on T1WI fat suppression （FS） and patchshape 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）. There were statistically significant differences between patients with pancreatic cancer and patients with AIP or normal population （P〈0.05） and no statistically significant difference between patients with AIP and with normal population （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 followup： 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 ＂sausagelike＂ and ＂false tumor like＂ changes, the nonneoplastic 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.