three series have reported the prevalence of autoimmune pancreatitis as between 5% and 6% of all patients with chronic pancreatitis .
it is very important to distinguish between these two entities regarding to differences in treatment and prognosis .
aip appears to be a disease of the elderly , but vary widely in age , as most patients are more than 50 years old at diagnosis .
it is reported to be at least twice as common in men as in women .
although diffuse swelling of the pancreatic parenchyma can be morphologically characteristic of aip , a focal type of this clinical entity has been recently recognized and is still difficult to establish . however , in this day and age , even with heightened awareness of aip and appropriate preoperative workup ( including serum immunoglobulin g fraction 4 ( igg4 ) measurement and , in very select cases , a short steroid trial ) , some patients with aip are likely to be resected for the suspicion of malignancy .
a 56-year - old patient was referred to our unit for upper abdominal pain since two week and lost of 6 kg in two months . in his past medical history
the serum carcinoembyonic antigen and cancer antigen 19 - 9 ( ca ) level was normal .
transabdominal ultrasonography showed a hepatic steatosis and 5 angiomas . magnetic resonance imaging ( mri ) showed the angiomas and a lesion of 2020 mm of the pancreatic tail with decreased signal intensity on t1-weighted mr images , increased signal intensity on t2-weighted mr images , and discreetly hypovascularized ( figure 1 ) . due to concerns of pancreatic malignancy ( pancreatic adenocarcinoma ) ,
we found a tumor about 5 cm in diameter lacking clear margins in the tail of the pancreas , which was removed via an open distal splenopancreatectomy .
histological analysis of the resected specimen revealed no malignancy , but dense fibrosis with lymphoplasmositic infiltration and acinar atrophy ( figure 2 ) .
postoperatively , autoantibodies and immunoglobulin were normal but igg4 was slightly above of the upper limit of the normal range .
patient was treated by 40 mg / j of corticotherapy with a remarkable improvement . in the follow up ,
because of the past medical history of mellitus diabetes , the young age of the patient , the normalization of the serum igg4 level , the absence of malignancy in histology , and the clinical improvement after corticoid therapy , the diagnosis of aip was made .
figure 1magnetic resonance imaging shows the affected pancreatic lesion involving tail with decreased intensity on the t1-weighted image ( a ) and increased intensity on the t2-weighted image ( b ) compared with the signal intensity in the liver .
magnetic resonance imaging shows the affected pancreatic lesion involving tail with decreased intensity on the t1-weighted image ( a ) and increased intensity on the t2-weighted image ( b ) compared with the signal intensity in the liver .
figure 2the histologic findings of the resected specimen of the pancreas include : dense fibrosis ( black arrow ) , lymphoplasmacytic infiltration , and acinar atrophy ( white arrow ) .
hematoxylin and eosin ( he , 250 ) . the histologic findings of the resected specimen of the pancreas include : dense fibrosis ( black arrow ) , lymphoplasmacytic infiltration , and acinar atrophy ( white arrow ) .
although diagnostic criteria were established for aip , there remains no practical strategy to differentiate pc from aip .
making a correct differential diagnosis between the two conditions is of paramount importance as the treatment approaches are different .
the common presenting symptoms of the pseudo tumoral autoimmune pancreatitis are mild abdominal pain , jaundice , and weight loss .
cholestatis was seen in 75100% of a japanese series , mild pancreatitis , acute recurrent pancreatitis , biliary duct strictures are a various clinical forms of aip .
it is made by radiologic computed tomography scan finding of a narrowing of the pancreatic duct and parenchymal edema of the pancreas ( a sausage shape ) .
isolated focal pancreatic mass is difficult to be diagnosing without doubt as a focal aip .
it can show focal aip as a low - attenuation or an iso - attenuation mass .
on the other hand , features highly suggestive of pancreatic cancer were a pancreatic low density mass , main pancreatic duct obstruction , distal pancreatic atrophy , and metastases .
endoscopic ultrasonography provides the opportunity for fine needle aspiration , but does not have pathognomonic findings on its own .
immunological abnormalities include hypergammaglobulinaemia , elevated serum igg4 levels and the presence of autoantibodies including antinuclear antibody , anti smooth muscle antibody , rheumatoid factor , antilactoferrin antibody and anticarbonic anhydrase antibody ii .
the specificity and sensitivity of a high serum igg4 level in the diagnosis of aip are > 90% .
after resection , histological changes in aip show predominantly periductal inflammation consisting of a dense interstitial lymphoplasmacytic infiltrate , thus causing duct obstruction with acinar tissue fibrosis .
in addition , aip has been seen in association with retroperitoneal fibrosis , kidney involvement and lung nodules .
these features are considered as extrapancreatic signs of aip and might be helpful to diagnose especially in focal form .
our patient had no extrapancreatics features . because of the difficulty of the diagnosis , several types of diagnosis criteria have been proposed . since there is currently no diagnostic serological marker for aip , and approach to the pancreas of histological examination is generally difficult , aip is currently diagnosed on the basis of presence of a combination of abnormalities unique to aip . for practical purposes , the revise japanese clinical diagnostic criteria ( 2006 ) and hisort criteria from the mayo clinic and in 2011 international consensus diagnostic criteria for aip were proposed .
in this set of diagnostic criteria , the diagnosis of aip is made using one or more positive criteria on : i ) imaging criteria : diffuse enlargement of the pancreas and diffuse or segmental irregular narrowing of the main pancreatic duct ; ii ) laboratory criteria : elevated levels of igg and/or igg4 or the presence of autoantibodies ; iii ) histopathologic criteria : fibrosis and lymphoplasmocytic infiltration ; iv ) association with other autoimmune diseases ; and v ) response to steroid therapy . despite all these investigations procedures and the existence of these criteria ,
35% of patients undergoing pancreatic resection for presumed pc in fact has aip , as was the case of our patient .
reported that 7 of 37 ( 18.9% ) aip patients had surgery because they were misdiagnosed as having pc or bile duct cancer .
this treatment may represent a diagnosis test , considered as one of the main diagnosis criteria .
extrapancreatic features , igg4 level , endoscopic ultrasound guided fine needle aspiration and corticotherapy are helpful to evoke aip .
the preoperative diagnosis should prevent unnecessary surgery causing a high morbidity comparing to medical treatment ( corticosteroid ) of aip .
 autoimmune pancreatitis ( aip ) is a rare disorder , although the exact prevalence is still unkown . 
 it is a type of pancreatitis that is presumed to have an autoimmune aetiology , and is currently diagnosed based on a combination of 5 criteria . 
 however , in this day and age , some patients with aip are likely to be resected for the suspicion of malignancy . 
 the authors report a case of pseudo - tumoral autoimmune pancreatitis , reviewing some literature about it and underlining the difficulty in the diagnosis . 
 a 56-year - old patient was referred to our unit for upper abdominal pain . in his past medical history 
 we note mellitus diabetes . 
 the clinical examination was unremarkable . 
 laboratory data showed no abnormal values . 
 upper endoscopy showed antral gastritis . 
 transabdominal ultrasonography showed a hepatic steatosis and 5 angiomas . 
 no computed tomography scan was made . 
 magnetic resonance imaging ( mri ) showed 5 angiomas and a lesion of 2020 mm of the pancreatic tail with decreased signal intensity on t1-weighted mr images , increased signal intensity on t2-weighted mr images . due to concerns of pancreatic malignancy , 
 the patient underwent open distal spleno - pancreatectomy . 
 histolo gical analysis of the resected specimen revealed no malignancy . 
 postoperatively , immunoglobulin g fraction 4 was slightly above of the upper limit of the normal range . 
 after corticotherapy the patient is getting better . 
 this case underlines the difficulties still encountered in the diagnosis of aip . 
 it has been frequently misdiagnosed as pancreatic cancer and caused unnecessary resection . in order to avoid unnecessary resections for an otherwise benign and easily treatable condition 
 , it is urgent to refine diagnostic criteria and to reach an international consensus . 