a non - parasitic splenic cyst is a rare condition with an incidence of 0.07% as reported in a review of large autopsy cases ( 1 ) . splenic epidermoid cysts are rare benign primary cysts that account for 10% of non - parasitic splenic cysts ( 2 ) . epidermoid cysts occasionally arise from accessory spleens , and those lesions in the pancreas are usually associated with intrapancreatic accessory spleens ( 3 ) . we herein describe a rare case of an epidermoid cyst in the pancreatic tail that invaginated from the spleen . surgical resection was performed due to drastic changes in imaging findings after an 11-year follow - up . in 1999 , a 46-year - old japanese woman with a history of acute nephritis was referred to our hospital for investigation of her renal dysfunction . she was diagnosed with chronic glomerulonephritis , and multi - locular cysts in the pancreatic tail were also discovered incidentally . the patient had no history of abdominal pain or a fever , and the findings on a physical examination were unremarkable . the blood tests showed elevated levels of blood urea nitrogen and creatinine , but normal levels of cancer antigen 19 - 9 , carcinoembryonic antigen , and dupan-2 . magnetic resonance imaging ( mri ; fig . 1 ) and endoscopic ultrasonography ( eus ; fig . cyst fluid obtained by eus - guided fine needle aspiration ( eus - fna ) revealed no malignant cells , and follow - up was recommended for the patient . in 2000 , a new cystic lesion located between the initial cysts and the spleen was discovered ( fig . 1 , arrow ) , and the lesion grew slightly over the next three years . in 2010 , additional 2-cm cystic lesions were discovered ( fig . 1 , arrowhead ) with lower intensity on t2-weighted mri than the other cysts ( fig . t2-weighted mri of the multi - locular cysts in the pancreatic tail during 11-year follow - up . several new cystic lesions ( arrow ) were detected between the index lesions and the spleen in 2000 . in 2010 , an additional lesion , 2 cm in size , was observed in the splenic hilum ( arrowhead ) ; the images in 2009 also showed the presence of the new lesion retrospectively . the patient remained asymptomatic , and blood tests showed that only the levels of elastase were elevated . eus also revealed multi - locular cysts with thickened septa surrounded by a capsule ( fig . re - sampling of the cyst fluid by eus - fna once again was negative for malignancy . since bleeding into the pancreatic cysts was suspected , distal pancreatectomy was performed . 
 the endoscopic ultrasound images . imaging revealed a cystic lesion in the pancreatic tail with multi - locular lesions in 1999 . eleven years later , the lesion had enlarged with thick septa . 
 
 a multi - planar reconstruction image of the mri findings before distal pancreatectomy . the intensity of the additional cystic lesions ( arrowhead ) was lower than that of the other cysts . a pathological examination revealed a lesion measuring 5.55.03.5 cm in size in the pancreatic tail containing multi - locular cysts . these cysts were lined with benign multi - layered flattened epithelium that was positive for high - molecular - weight keratin ( 34be12 ) and cytokeratin 5/6 . most of the cysts were surrounded by a thin layer of red - colored tissue consisting of cells positive for cd8 and cd68 . this layer was connected to the spleen ; therefore , this multi - locular pancreatic cyst was diagnosed to be an invaginated splenic epidermoid cyst ( fig . a ) grossly , the cut surface of the pancreas and spleen showed a lesion measuring 5.55.03.5 cm in the pancreatic tail containing multi - locular cysts . most of the cystic lesions were surrounded by a thin layer of red - colored tissue connecting to the spleen . ( b ) a microscopic analysis showed that the cysts were lined with multi - layered flattened non - neoplastic epithelium positive for high - molecular - weight keratin ( 34be12 ) and cytokeratin 5/6 . the thin layer surrounding the cysts consisted of cells positive for cd8 and cd68 , demonstrating that the layer was normal splenic pulp tissue . to our knowledge , this is the first report of an epidermoid cyst in the pancreatic tail that invaginated from the spleen . both pancreatic and splenic epidermoid cysts are extremely rare benign primary cysts ( 1 - 3 ) . pancreatic epidermoid cysts usually arise from intrapancreatic accessory spleens and are characterized by non - neoplastic keratinizing epithelium surrounded by splenic parenchyma ( 3 ) . in this case , the cysts were surrounded by splenic parenchyma and directly connected to the spleen , suggesting an invagination from the splenic hilum rather than arising from an accessory spleen . three hypotheses have been proposed regarding the pathogenesis of epidermoid cyst of the spleen or intrapancreatic accessory spleen : the mesothelial invagination theory , the lymph space theory , and the endodermal inclusion theory ( 2 ) . in our case , the congenital cyst lined and surrounded with splenic parenchyma appeared to be invaginating into the pancreas from the spleen , conforming to the endodermal inclusion theory . this finding also supports the notion that epithelial splenic cysts do indeed develop metaplasia of heterotopic endodermal inclusion within the spleen ( 3 ) . since the multi - locular cyst in the current case was localized mainly to the pancreas , the preoperative diagnosis was a benign pancreatic cyst . pancreatic epidermoid cysts are usually identified incidentally and are frequently recognized as neoplastic cysts , such as mucinous cystic neoplasms or intraductal papillary mucinous neoplasms of the pancreas ( 3 ) . conservative observation was conducted in only four previous reports , but for much shorter periods than in the present case , ranging from 4 months to 3 years ( 4 - 7 ) . in these five patients , including ours , enlargement of the cysts was seen in three cases over time ( 4,7 ) , suggesting that epidermoid cysts in the pancreas may sometimes increase in size . we described a rare case of an epidermoid cyst in the pancreatic tail that invaginated from the spleen , strongly supporting the endodermal inclusion theory . the emergence of satellite lesions and the enlargement of the cyst were observed during the 11-year follow - up , suggesting that epidermoid cysts may increase in size over time .
epidermoid cysts arising from both the pancreas and spleen are rare . 
 we herein report a case of a surgically resected epidermoid cyst in the pancreatic tail invaginated from the spleen . a multi - locular cyst , 
 2 cm in diameter , without a solid component was discovered incidentally in the pancreatic tail . during the 11-year follow - up , 
 the emergence of satellite cystic lesions with distinct appearances was seen , and surgical resection was selected despite the lack of any associated symptoms or evidence of cytological abnormalities . 
 histologically , these cysts were lined with benign multi - layered flattened epithelium surrounded by a thin layer consisting of cells positive for cd8 and cd68 and connecting to the spleen .