ECIPAS is an extremely rare entity. ECIPAS was thought to be benign until recently malignant transformation was found during 6-years follow-up[10]. Li et al[11] reviewed 56 cases of ECIPAS since the first case was diagnosed by Davidson et al in 1980[12]. Most of the cases were incidentally detected, while the others had symptoms of abdominal pain, discomfort, nausea, vomiting, back pain, fever, or weight loss. In all cases, the cystic lesions were found in the pancreatic tail. The cysts could be either unilocular or multilocular, lined by a keratinized or nonkeratinized stratified squamous epithelium or a cuboidal epithelium. The average cyst size was 4.3 cm (range 1.3–15 cm). Although most cases of ECIPAS were benign, it was necessary to differentiate it from other potentially malignant pancreatic tail cystic neoplasms, including MCN, SPT, pseudocyst, IPMN and cystic pancreatic neuroendocrine tumor (p-NET).
Elevation of serum CA19-9 level was common in ECIPAS patients. Hu et al reported that nearly 40% of ECIPAS showed high levels of CA19-9[5, 13], hence increasing the difficulty to distinguish ECIPAS from malignant tumors preoperatively. It has been reported that the squamous epithelial lining of ECIPAS expressed CA19-9 in an immunohistochemical analysis, and serum CA19-9 levels markedly decreased to normal levels postoperatively in patients[14]. These findings suggest that serum CA19-9 is secreted by the epithelial lining cells of ECIPAS. In the current case, although ECIPAS was speculated, the symptoms and high CA19-9 level encouraged us to perform surgery.
Preoperative diagnosis of ECIPAS is difficult. MCN, cystadenocarcinoma, pseudocyst, cystic p-NET or potential malignant tumor is suspected in most cases[15–18]. Including the present case, only six (10.7%) among the 56 reported cases were correctly diagnosed preoperatively[15, 19–22]. Most cases of ECIPAS were diagnosed after surgery based on the pathological findings[23]. Advances in imaging techniques facilitated the diagnosis of ECIPAS as compared with previously; however, few studies have reported the imaging characteristics of ECIPAS. ECIPAS is a well-defined, unilocular or multilocular cystic mass located in the tail of the pancreas on multimodality imaging. The well-defined boundary is a differentiating morphological feature suggestive of a benign tumor. The cystic wall of ECIPAS showed contrast enhancement similar to that of the spleen during multiphasic CT or MRI. Therefore, the accessory spleen surrounding the cyst was a key component for correct diagnosis. However, only a few cases of ECIPAS had a sufficient solid component that allowed splenic tissues be detected through radiological imaging. Fortunately, there was a large amount of solid tissue present in our case; therefore, correct preoperative diagnosis of ECIPAS was achieved. Including the present case, four of 56 cases were diagnosed as ECIPAS preoperatively based on the similar density on enhanced CT and intensity on MRI between the solid component and the spleen[15, 20, 21]. The cystic component of ECIPAS usually appears to be hypodense on nonenhanced CT, hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging. However, it sometimes appears hyperdense on nonenhanced CT and hyperintense on T1-weighted imaging, in the presence of hemorrhage or keratinized materials within the cyst[5, 24, 25]. In the present case, the cystic component was hyperdense on nonenhanced CT and hyperintense on T1-weighted imaging, and remained unenhanced during multiphasic scans. Thus, the cystic content was considered to be mucinous or bloody liquid that was confirmed by the resected specimen following surgery.
EUS-FNA is a commonly used technique to evaluate pancreatic masses, and it has been investigated for diagnosis of ECIPAS. In Tatsas et al’s report, three of six cases of intrapancreatic accessory spleen were diagnosed successfully; however, one case of ECIPAS failed to be diagnosed by EUS-FNA[26]. In the only case of ECIPAS diagnosed postoperatively, the FNA sample revealed only predominant macrophages and proteinaceous debris; therefore, no pathological evidence of ECIPAS was acquired prior to surgery[26]. Among the remaining five cases of ECIPAS reported in the English-language literature, one was correctly diagnosed by EUS-FNA[17, 21, 27–29]. Matsumoto et al reported a case of ECIPAS that was accurately diagnosed by EUS-FNA[21]. Their histological findings showed that sinusoids and abundant polymorphous lymphocytes were consistent with an intrapancreatic accessory spleen[21]. Therefore, to acquire pathological evidence of ECIPAS using EUS-FNA seems to be difficult. This is mainly because the amount of splenic tissue surrounding the epidermoid cyst was too small in most cases to be successfully aspirated by FNA. In the present case, although leukocytes were found, we failed to reveal splenic sinusoids and endothelial cells within the acquired specimen.
Treatment of ECIPAS consists of surgical resection and follow-up. As most cases of ECIPAS are reported not to have malignant potential, unnecessary surgery can be avoided with a correct preoperative diagnosis. However, in cases of ECIPAS with symptoms, or in those in which it is difficult to completely exclude malignancy, laparoscopic spleen-preserving distal pancreatectomy is suggested since this procedure has been commonly used to treat benign or low-grade malignant tumors of the pancreatic tail. Fujii et al[30] reported that laparoscopic distal pancreatectomy could be a useful, minimally invasive surgical approach for treating ECIPAS with additionally decreased postoperative pain, length of stay and associated mortality and morbidity. In the present case, the symptoms and serum CA19-9 level encouraged us to perform surgery in this patient. The patient recovered uneventfully and had no evidence of tumor recurrence during 2-years follow-up, suggesting laparoscopic spleen-preserving distal pancreatectomy is effective and safe for ECIPAS.
In conclusion, it is difficult to make an exact diagnosis of pancreatic tail cystic lesions preoperatively. ECIPAS is an exceedingly rare entity, and all cases reported so far have been found in the pancreatic tail. Therefore, although rare, ECIPAS should be considered in the differential diagnosis of pancreatic tail cystic lesions. Imaging and endoscopic evaluation may be helpful in the diagnosis, but preoperative diagnosis is still challenging. A similar enhancement between the solid component of the cystic lesions and the splenic parenchyma is critical for correct diagnosis. Treatment of ECIPAS by laparoscopic distal pancreatectomy is an effective procedure with the advantages of minimal invasiveness.