igg4-related pancreatitis has been recognized as a unique form of autoimmune pancreatitis ( also known as type 1 autoimmune pancreatitis ) , the histology of which consists of lymphocytic and igg4-positive plasma cell infiltration , storiform fibrosis , and obstructive phlebitis . these fibro - inflammatory lesions are found at multiple , different anatomical sites , together with serum igg4 elevation , indicating that the condition is regarded not as a local immune response but a systemic disorder ( igg4-related disease ; igg4-rd ) . recent studies revealed that approximately 0.5% to 1.0% of patients with igg4-related pancreatitis or type 1 autoimmune pancreatitis are diagnosed with pancreatic cancer concurrently or during follow - up after the pancreatitis diagnosis . on the other hand , approximately 10% of patients with pancreatic cancer have concomitant serum igg4 elevation or moderate - to - marked igg4-positive plasma cell infiltration . taken together , these data support a close association between pancreatic malignant processes and igg4-positive plasma cell  associated inflammation . herein , we report the first case , to our knowledge , of combined igg4-related pancreatitis and solid pseudopapillary neoplasm ( spn ) , a rare low - grade malignant tumor . a solid and cystic lesion of the pancreatic tail was incidentally found in a 62-year - old woman with no significant past medical history . the lesion appeared as a 3-cm low - density area in the pancreatic tail on abdominal computed tomography ( ct ) . there was no diffuse radiological change in the pancreas or main pancreatic duct , probably owing to the distal location of the pancreatic lesion . contrast - enhanced ct showed narrowing of the splenic vein and development of collateral circulation , suggesting that this pancreatic lesion was associated with venous invasion . the lesion was diagnosed as an spn on endoscopic ultrasound - guided fine needle aspiration ( eus - fna ) , and distal pancreatectomy was performed . histologically , the solid and cystic tumor was surrounded by pancreatic fibro - inflammatory stroma ( figure 1 ) . the tumor cells showed relatively small , round nuclei and papillary - like architecture in a hemorrhagic background ( figure 2a ) . on immunohistochemical examination , the tumor cells were diffusely positive for nuclear -catenin ( figure 2b ) and cytoplasmic dot - like cd10 ( figure 2c ) . the tumor cells were focally positive for synaptophysin and cd56 , while they were negative for chromogranin a and trypsin . consistent with the diagnosis based on eus - fna biopsy , we diagnosed the patient with an spn of the pancreas . ( a ) hematoxylin and eosin ( he ) staining , ( b ) elastica van gieson ( evg ) staining , and ( c ) -catenin immunostaining of the cross - section of the pancreatic tail . -catenin immunostaining reveals areas of the tumor cells , normal pancreatic tissue , and igg4-related pancreatitis that are strongly positive , weakly positive , and negative , respectively . according to -catenin immunoreactivity note that evg staining reveals a venous - like structure around the tumor nests ( see also figure 2d , black arrow ) , which is likely the splenic vein . representative images of a solid pseudopapillary neoplasm ( spn ) of the pancreas and igg4-related pancreatitis . hematoxylin and eosin ( he ) staining ( a ) , -catenin immunostaining ( b ) , cd10 immunostaining ( c ) , and elastica van gieson ( evg ) staining ( d ) of an spn . evg staining of obstructive phlebitis ( e ) , he staining of storiform fibrosis ( f ) , and he staining ( g ) , igg immunostaining ( h ) , and igg4 immunostaining ( i ) of dense lymphoplasmacytic infiltrates . igg and igg4-immunostaining reveals that a ratio of igg4/igg - positive plasma cells of approximately 45% and > 50 igg4-positive plasma cells / high - power field . scale bars = 100 m ( a - c and g - i ) , 200 m ( e and f ) , or 500 m ( d ) . in order to identify the venous invasion observed on radiological examinations , we performed elastica van gieson staining . interestingly , we found not only a venous - like structure around the tumor nest ( figure 2d ) but also obstructive phlebitis in the surrounding stroma ( figure 2e ) . in addition , the surrounding stroma exhibited storiform - type fibrosis ( figure 2f ) and was associated with dense lymphoplasmacytic infiltrates ( figure 2 g ) . igg and igg4-immunostaining revealed a ratio of igg4/igg - positive plasma cells of approximately 45% and > 50 igg4-positive plasma cells / high - power field ( figure 2h and 2i ) . subsequently , we measured the patient s postoperative serum igg4 level , which was within normal limits , and no other sclerotic lesion was found on radiological assessment , suggesting that the patient had no evidence of igg4-rd . the patient has received no additional therapy and exhibited no disease recurrence for 15 months postoperatively . spn is a rare pancreatic tumor that does not differentiate along any particular lineage , and almost all spns harbor a somatic mutation in exon 3 of -catenin . spn is classified as a low - grade malignant tumor , in that direct extension or metastasis is sometimes found in the surrounding organs , for example , stomach and spleen . in the present case , the tumor cells invaded the splenic vein , and collateral circulation subsequently developed . most patients lack the above - mentioned typical histology of igg4-related pancreatitis , suggesting that these phenomena should be distinguished from igg4-related pancreatitis and/or igg4-rd . however , the pathological significance of these nonspecific igg4-positive plasma cell infiltrations is unknown , and it is not clear whether a routine search for igg4-positive plasma cell infiltration should be made in pancreatic cancer . in addition , a clear distinction between the fibrotic phase of igg4-rd and nonspecific igg4-positive plasma cell infiltration is difficult , even with a sufficient surgical specimen . in the present case , the observed fibro - inflammatory changes fulfilled the histological criteria of igg4-related pancreatitis , although the fibro - inflammatory changes were limited to the zone immediately surrounding the tumor . in addition to the histological distribution , clinical and radiological findings favor the diagnosis of a stromal reaction to the tumor over true igg4-rd . further investigation of combined pancreatic neoplasia and igg4-positive plasma cell infiltration with or without histology associated with typical igg4-related pancreatitis is needed . bateman et al described the link between intraductal papillary mucinous neoplasm of the pancreas and igg4-rd . of 14 intraductal papillary mucinous neoplasm cases , 2  index  cases showed most of the key clinical and histological features of igg4-rd , although data on serum igg4 concentration were not available . on the other hand , the other 12 cases lacked the findings of obstructive phlebitis and storiform - type fibrosis , and some of them contained a small amount of igg4-positive plasma cell infiltrates . taken together , these key clinical findings are essential for the diagnosis of igg4-rd , and the boston criteria can be used to distinguish type 1 autoimmune pancreatitis / igg4-rd from other nonspecific chronic inflammations of the pancreas . obstructive phlebitis is frequently found in the various affected organs , except for the lacrimal glands and lymph nodes . this angiotropic fibro - inflammation may be important for clarifying the detailed mechanism of igg4-rd . in the present case , obstructive phlebitis in the surrounding stroma supported the presence of igg4-related pancreatitis , and possibly contributed to the development of collateral circulation through the blockage of minor veins . eus - fna is a relatively new , safe , and less invasive diagnostic technique to obtain a histological specimen that is sufficient to diagnose pancreatic lesions , including pancreatic tumors and igg4-related pancreatitis . to confirm igg4-related pancreatitis without histological examination is a diagnostic challenge , because some cases mimic neoplasia to form a pancreatic mass . this technique allows the choice of an optimal treatment according to the pathological diagnosis of the pancreatic disease . malignant disease requires surgery and/or chemo - radiation , whereas steroid therapy is appropriate for treating autoimmune pancreatitis . however , a small sample obtained using eus - fna may be inadequate to diagnose combined neoplastic and fibro - inflammatory lesions , especially if the distribution of the 2 lesions is distinguished in the pancreatic mass ( figure 1 ) . for diagnosing combined pancreatic disease , surgical resection is probably required to confirm global lesion features . similar to pancreatic cancer , this low - grade malignancy is also rarely associated with igg4-related pancreatitis . to avoid misdiagnosis of a combined pancreatic neoplasm and fibro - inflammatory lesion , pathologists should consider such situations and make a definitive diagnosis after careful observation of all pancreatic lesions .
a solid and cystic pancreatic lesion was incidentally found in a 62-year - old woman on abdominal computed tomography . 
 the lesion was diagnosed as a solid pseudopapillary neoplasm by using endoscopic ultrasound - guided fine needle aspiration , and the tumor was resected . 
 histologically , the tumor cells had relatively small , round nuclei and papillary - like architecture in a hemorrhagic background . on immunohistochemical examination , 
 the tumor cells were diffusely positive for nuclear -catenin and cytoplasmic cd10 . 
 in addition , typical histological findings of igg4-related pancreatitis ( obstructive phlebitis , storiform - type fibrosis , and abundant igg4-positive plasma cell infiltration ) were found in the surrounding stroma of the solid pseudopapillary neoplasm . 
 postoperative workup failed to detect any other sclerotic lesions or serum igg4 elevation , suggesting that the patient had no evidence of igg4-related disease . to avoid misdiagnosis of a combined pancreatic neoplasm and fibro - inflammatory lesion 
 , pathologists should consider such situations and make a definitive diagnosis after careful observation of all pancreatic lesions .