Cystic neoplasms of the pancreas are being identified with increasing frequency. Cystic lesions are roughly classified into epithelial cells' lined cysts and cystic degenerative lesions, and each includes non-neoplastic and neoplastic lesions. The former includes retention cyst, serous cystic neoplasms (SCNs), mucinous cystic neoplasms (MCNs), intraductal papillary mucinous neoplasms (IPMNs), lymphoepithelial cysts and others, and the later includes pseudocysts, solid pseudopapillary neoplasms (SPNs) and several solid tumors showing degenerative change and cystic formation. Cystic neoplasms include benign to malignant neoplasms. It is important to recognize these before invasive carcinoma develops, especially in MCNs and IPMNs. The histologic types and clinicopathological features of major cystic lesions are discussed.

IPMNs are histologically classified as adenoma, non-invasive carcinoma and invasive cancer, therefore the treatment strategy is important. The revised guideline reported in 2017 highlighted several points in the high-risk stigmata and worrisome futures were revised. In addition surgery is recommended for, definite MNs measuring ≥5mm by EUS.

At initial diagnosis of suspicious IPMNs, US, CT and MRCP are recommended for differentiation from other pancreatic disease. In addition, EUS is indicated in order to evaluate the size of MN more correctly and to detect concomitant pancreatic ductal adenocarcinoma (PDAC). For surgery candidates, ERCP, IDUS and POPS are mandatory for the evaluation of tumor extension.

On the other hand, careful attention should be paid to not only the progression of IPMN, but also the development of concomitant PDAC during follow-up. Although surveillance is recommended to be performed according the size stratification in the guidelines, frequencies of progression and malignant transformation in the BD-IPMN without any sign of malignancy have been reported as low. We propose the surveillance of BD-IPMN with follow-up by CT or MRCP alternating with EUS every 6 months, regardless of cyst size.

If an intraductal papillary mucinous neoplasm (IPMN) has invasive components, lymph node metastases or postoperative extra-pancreatic recurrence may occur, resulting in decreased survival of patients with invasive intraductal papillary mucinous carcinoma (IPMC) compared to patients with noninvasive IPMN. Therefore, we suggest that IPMNs should be resected before the tumor progresses to invasive IPMC, in order to prolong survival. Regarding the operative approach, regional lymph node dissection similar to that used for pancreatic cancer might be needed for invasive IPMC to prevent postoperative local recurrence. Instead of total pancreatectomy, an operation to preserve pancreatic parenchyma should be considered to maintain long-term endocrine and exocrine function if the resection margin does not have high-grade dysplasia or invasive IPMC. If there is a recurrence in the pancreatic remnant after resection, remnant pancreatectomy may prolong the survival of patients with IPMN with recurrence in the remnant. Long-term surveillance might be necessary to evaluate the pancreatic remnant for recurrence after surgical resection of IPMN.

Pancreatic mucinous cystic neoplasms are cystic lesions which appear commonly in the pancreatic body and tail in middle-aged females, and have a characteristic macroscopic description referred to as "orange like shape", or "cyst in cyst". In 2007, a multi-institutional retrospective observational study of MCN with ovarian type stroma was conducted by the Japan Pancreatic Society. Clinicopathological features and long-term prognosis were described based on 156 collected MCN cases in this study. For the diagnosis of MCN, capturing the characteristic clinical and pathological features using imaging modalities such as US, CT, MRI, and EUS is necessary. Cyst fluid analyses were also considered for difficult cases. Although diagnosing typical MCN is relatively easy, care should be taken when diagnosing atypical cases.

In this report we review the surgical management of MCN. Some large-scale retrospective studies have proposed the resection of all MCNs while others opted for surgical procedures based on malignant predictors. On the other hand, reports of lesions with a small cyst diameter, mural nodules without malignancy suggested detailed follow-up observations. The natural history of MCN has not yet been fully elucidated making the, non-surgical management difficult as it requires long-term expensive diagnostic imaging, and invasive cancer can not be reliably identified, thus making surgical resection the primary treatment option. Suspected invasive cancer is an indication for pancreatectomy with lymph node dissection as well as ductal cancer. However, in cases where malignancy is not suspected, organ-preserving surgery, taking into consideration the long-term quality of life after surgery, is indicated.

Pancreatic surgery requires a great level of expertise and it is recommended that cases requiring surgical intervention be performed in high-volume centers staffed with highly experienced, well-trained pancreatic surgeons.

Serous cystic neoplasms (SCN), relatively rare cystic tumors representing 1-2% of pancreatic tumors, have small cysts composed of glycogen-rich clear cells in a honeycomb configuration (honeycomb appearance) (microcystic). Recent developments in diagnostic imaging show the characteristic macroscopic morphology. A wide range of cases reveal diverse macroscopic morphology. This lesion is included in the differential diagnosis with other pancreatic lesions having malignant potential. There are a few reports of malignancy, so care must be taken in handling these lesions. The average age ranges from 56.6 to 62.1 years, and 75 to 86% are in women. As many as 53 to 68% have symptoms, the average tumor diameter is about 5cm, and have been reported up to 22cm. These lesions can occur in any part of the pancreas. A typical example of SCN is the microcystic type, which is a collection of microcysts, but there are also macrocystic types in which the constituent cysts are as large as several centimeters and macroscopically show multiloculated cystic tumors. The mixed type is a mixture of both microcystic type and macrocystic types. Although rare, there is also a solid type that looks solid macroscopically. If the lesion exceeds 4cm, aggressive resection is desirable. The most important point regarding diagnosis is that only 53 (61%) of lesions were preoperatively diagnosed as SCN, among 87 patients treated for SCN based on postoperative pathological diagnosis, and in the remaining 34 (39%) SCN was not considered in the diagnosis. Conversely, even if SCN is considered the most likely diagnosis, it may be a different type of tumor. Therefore, for lesions diagnosed as SCN preoperatively, both doctor and patient must consider follow-up without undergoing surgery.

The diagnostic approach to pancreatic cystic neoplasms has gradually improved based on the International Consensus Guidelines for IPMN and MCN of the pancreas. However, there are a variety of pancreatic lesions with cystic components. Several rare pancreatic neoplasms with cystic components that have malignant potential should be diagnosed carefully (e.g., pancreatic neuroendocrine tumors (pNET), solid-pseudo-papillary neoplasms (SPN), pancreatic acinar cell carcinomas (ACC), and anaplastic carcinomas). Although diagnostic imaging is frequently difficult and the final diagnosis is based on histological findings, it is important to master the characteristic imaging findings of each disease because they are sometimes hard to diagnose histologically. Herein, we present our clinical experience and review the management of these relatively rare pancreatic neoplasms.

Fistula formation associated with IPMN is rarely reported. A 72-year-old woman was admitted to our hospital for surgical treatment of IPMN. Over a 10 year period, the IPMN increased in size and dilatation of the MPD eventually penetrating the stomach. At the time of surgery, a tumor 16cm in diameter was palpable. En bloc total pancreatectomy with splenectomy and partial resection of the gastric body were performed. The histopathological examination of the resected specimen showed high grade dysplasia accompanied by minimally invasive mucinous carcinoma. The patient was discharged after an uneventful postoperative recovery. To date, she has received no adjuvant chemotherapy. After administration of enteric coated pancrealipase, her levels of serum albumin increased to 4g/dl. Her nutritional status has been good for more than 4 years after surgery.

The patient was a 63 year-old male, who first visited a primary care physician due to epigastric pain. Abdominal ultrasound revealed dilation of the main pancreatic duct and the patient was then referred to us for further evaluation. Although imaging examinations (abdominal ultrasound and contrast CT) did not show any tumors, pancreatic juice cytology revealed the presence of atypical cells, including clusters of atypical spindle cells, which led us to strongly suspect malignancy. We thus performed a pylorus-preserving pancreatoduodenectomy and the patient was diagnosed with a spindle cell-type anaplastic carcinoma of pancreas with invasive components measuring 6 mm in diameter.

Anaplastic carcinoma of the pancreas is a very rare histopathological subtype of pancreatic cancer and its incidence is reported to be 0.29% of all pancreatic neoplasms. It is defined by an absence of differentiation, and follows an aggressive clinical course. The disease also involves rapid growth and spread, therefore, the majority of cases are rarely detected at an early stage. In this case, the only abnormal finding by imaging examinations was the dilation of the pancreatic duct which led to the pathological diagnosis of a small early-stage lesion that measured only 6 mm in diameter. We report a case of spindle cell-type anaplastic carcinoma of the pancreas diagnosed by pancreatic juice cytology.