Pancreatic cyst fluid triage: a critical component of the preoperative evaluation of pancreatic cysts.

Pancreatic cysts are a complex group of benign, malignant, and premalignant lesions with diverse clinical, radiologic, and pathologic features. It is no longer believed that the vast majority of pancreatic cysts are pseudocysts, inclusion cysts, or benign neoplastic cysts that do not require follow-up. Our knowledge and understanding of neoplastic pancreatic cysts in general, and mucinous pancreatic cysts in particular, has grown exponentially since the 1980s when intraductal papillary mucinous neoplasm (IPMN) was recognized as a distinct entity from mucinous cystic neoplasm (MCN). Our realization that all neoplastic mucinous cysts have malignant potential has led to intensive evaluation of patients with both symptomatic and asymptomatic pancreatic cysts to determine the nature of the cyst and, thus, the possible need for resection. Now that we are looking closely, we know that pancreatic cysts are extremely common lesions. Approximately 2.6% of asymptomatic adults and>8% of adults aged>80 years who undergo abdominal imaging have a pancreatic cyst. The majority of these cysts are incidental cysts, and most are mucinous, but most are not malignant. Surgical resection of all pancreatic mucinous cysts is logistically impossible. Imaging may be very helpful for differentiating mucinous from nonmucinous cysts, but nearly 20% of serous cystadenomas are macrocystic with few septations, mimicking a mucinous cyst, whereas IPMNs can cause pancreatitis and simulate the appearance of a pseudocyst. In addition, imaging is not at all helpful in accurately differentiating lowgrade from high-grade dysplastic or even malignant mucinous cysts. The current paradigm of preoperative diagnosis uses clinical, radiologic, and pathologic methods to determine high-risk features of malignancy. One of the first questions to answer in cyst fluid analysis is whether the cyst is mucinous or nonmucinous. Most nonmucinous cysts are serous cysts. Just a few years ago, this distinction alone was sufficient to determine the need for surgery. Although serous cysts were resected primarily to relieve symptoms, all mucinous cysts, regardless of type, were resected because of the concern for malignant progression. What became clear from clinicopathologic analysis of these resected mucinous neoplasms was that there were distinct types of mucinous cysts, distinguished by sex, age, location in the pancreas, association with the pancreatic ducts, pathologic features, and likelihood of progression to cancer. Most MCNs are usually low-grade neoplasms that do not involve the main pancreatic duct. They are typically large, multiloculated cysts that occur primarily in the body or tail of the pancreas of young to middle-aged women. The current recommendation is to resect all MCNs regardless of grade, because intervention at diagnosis avoids long-term, expensive, annual surveillance.