Most PCNs are detected incidentally when abdominal imaging is performed for other indications . PCNs are categorized pathologically using the World Health Organization (WHO) classification . There are four types, which have varying malignant potential: IPMNs, MCNs, SCNs, and solid pseudo-papillary neoplasms. MCNs have ovarian-like stroma that is strongly immunostained for ER, PgR, and inhibin, but the other cystic tumors are not stained. Thus, the presence of ovarian-like stroma is essential for diagnosis of MCNs. Findings associated with malignant transformation in MCNs include large size (5 cm or larger in one series), a thickened or irregular cyst wall, an internal solid component or mass, and possible calcification of the cyst wall [5, 6, 10]. Previously, all MCNs were recommended to be resected based on their malignant potential. However, recently, a recommendation for resection is considered appropriate only for MCNs with malignant features such as positive cytology for a malignant neoplasm; a mucinous cyst ≥ 3 cm; Kras and/or guanine nucleotide-binding protein (G protein); α stimulating activity polypeptide (GNAS) mutation with tumor protein 53 (TP53) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α (PIK3CA); or phosphatase and tensin homolog deleted from chromosome (PTEN) mutation by molecular testing [2, 4]. In this study, surgery was performed in both cases because the tumor size was around 3 cm and showed enlargement [1,2,3].
There are three major guidelines regarding the treatment of MCNs, provided by The International Association of Pancreatology , The American Gastroenterological Association , and European experts’ consensus statements . These guidelines propose different treatments for MCNs as well as follow-up plans after surgery, and these differences cause confusion regarding the management of patients with MCNs. Depending on the global accumulation of MCN cases, a more concrete management algorithm is required.
Albores-Saavedra found that nine cases could have been non-mucinous cystadenomas of the pancreato-biliary phenotype and ovarian-like stroma during a review of 31 cases of tumors that were diagnosed as mucinous cystadenomas . All the patients were female with a mean age of 45 years. Seven tumors were symptomatic and tumor markers were within normal limits in all cases. Microscopically, the epithelial cells were lined by a single layer of cuboidal cells, and 2–3% of the epithelial cells included goblet cells. The septa of the cysts included spindle cells that resembled ovarian-like stroma. No dysplasia was found in either of the cases in the present study or in any of the cases reported by Albores-Saavedra. Although non-mucinous cystadenomas of the pancreato-biliary phenotype and ovarian-like stroma are insufficient evidence to determine the prognosis, it is suggested that it is better than for MCNs and SCNs, considering their pathological features. Albores-Saavedra reported nine cases (29%) with ovarian-like stroma but no mucin-producing cells, while the current study found two cases (9%). In fact, some tumors like these might be diagnosed as other typical cystic tumors, such as MCNs, SCNs, and simple cysts. For example, in Case 2, the tumor was initially diagnosed as SCN pathologically, because the cyst was filled with serous fluid, the stroma was not stained by inhibin, and the presence of spindle cells was not clear. WHO classification of the sensitivity of each immunostaining test regarding ovarian-like stroma is reported as follows: ER 30% and PgR 60–90% . The Japanese Multi-institutional Retrospective Observation Study of MCNs reported the sensitivity as follows: ER 78% and PgR 88% . There is no report of the sensitivity of the inhibin immunostaining rate. Albores-Saavedra reported that all the spindle cells expressed ER and PgR but only five of eight cases (62.5%) expressed inhibin . These results suggest that PgR is the most useful tool to investigate ovarian-like stroma. When it is difficult to use HE staining to evaluate ovarian-like stroma, staining the cystic tumor using PgR is required or the use of multiple tools such as PgR plus ER.
When it is difficult to diagnose the type of cystic tumor preoperatively, EUS–fine-needle aspiration (FNA) is often reported to be a useful tool [7, 11, 12]. In the present study, CT and MRI showed no septa or nodules in the cysts but EUS could detect the septa. However, EUS has low sensitivity and EUS–FNA has a high risk of tumor dissemination, and sometimes it is difficult to diagnose pathologically because of the low number of cells. Recently, EUS-guided through-the-needle forceps biopsy (EUS–TTNFB) has been performed as a new diagnostic tool for cystic tumors . In the DETECT study, which investigated the utility of EUS–TTNFB, the sensitivity of dual through-the-needle imaging (cytology and needle-based, confocal laser-induced endomicroscopy) of pancreatic cysts was about 100%. Some complications such as pancreatitis have been observed; however, it is expected to become a safer procedure in the next few years. It is anticipated that a useful tool like this will be available in the future for accurate preoperative diagnosis of cystic tumors.