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Ciliated foregut cyst of the pancreas: A benign lesion with elevated CEA levels

Dear Dr. Bedrossian: Pancreatic cystic lesions represent a challenge for the practicing cytopathologist. Ciliated foregut cysts are congenital cysts arising in relation to the development of the gut and the tracheobronchial tree, and they may occur in a number of sites, most commonly in the mediastinum. This rare type of congenital benign cyst may also occur in the subdiaphragmatic region, most frequently in the liver. Conversely, pancreatic ciliated foregut cysts are very uncommon. The cytopathologist must be aware of their occurrence to avoid overdiagnosis of mucinous neoplastic cysts. Noteworthy, pancreatic foregut ciliated cysts frequently feature elevated intracystic carcinoembryonic antigen (CEA) levels, leading to a worrisome clinical presentation. In this setting, the cytopathologist’s role is crucial. The case of a ciliated foregut cyst of the pancreas is illustrated here that was recently encountered in our endoscopic ultrasound (EUS)-pancreatic fine needle aspiration (FNA) practice. In a 50-year-old female, a cystic pancreatic lesion was incidentally discovered by computerized tomography, and it was further investigated by EUS. The cyst was located in the pancreatic head and measured 19 3 9 mm (Fig. 1a). The FNA, performed under EUS guidance, yielded only a few drops of fluid. In our institution, all pancreatic cystic FNAs are routinely performed according to a reference protocol wherein a cytopathologist prepares on site an ethanol-fixed smear for Papanicolaou staining and aliquots the residual material to measure the CEA levels. Microscopically, in a background rich in contaminating normal duodenal cells, loosely cohesive clusters of columnar cells were evident (Fig. 1b). At a higher magnification, these columnar cells displayed a ciliated apical pole and basal, small, round-to-oval normal nuclei (Fig. 1c). Occasionally, a cytoplasmic mucin vacuole displaced and compressed the nucleus (Fig. 1d). In spite of the CEA levels being elevated (190 ng/mL), the cytology enabled the diagnosis of pancreatic ciliated foregut cysts. Congenital foregut cysts have been diagnosed by EUS-FNA in the mediastinum (most common), liver, and other sites along the hepatobiliary system. The cysts are usually lined by a layer of pseudostratified ciliated epithelium with occasional goblet cells. Foregut cysts arising in relation to the liver and pancreas are hypothesized to originate from a detached outpouching of the primitive foregut, sequestered by the liver and pancreatic tissue during embryological development. Cases diagnosed in the pancreas are rare, being frequently misdiagnosed as pancreatic mucinous cystic neoplasms due to the elevated CEA levels. The standard for pancreatic cyst management includes both cytology and CEA level analysis. In fact, the latter can discriminate between cysts that are mucinous or nonmucinous, but only cytomorphology can differentiate between benign and malignant cysts. Unfortunately, a consensus on the cut-off of intracystic CEA levels is still lacking. The majority of studies have shown that the range from 110 to 200 ng/mL is approximately 80% accurate for identifying a cyst as mucinous. Raising the cutoff value improves the specificity of the test, but decreases its sensitivity. The CEA level in our case was elevated, suggesting the diagnosis of a mucinous cyst. However, in this case, the cytomorphology (Fig. 1b–d) easily ruled out the diagnosis of a mucinous cystic neoplasm. In fact, the presence of the ciliated epithelium was diagnostic of a benign ciliated foregut cyst. *Correspondence to: Giancarlo Troncone, M.D., Ph.D., Dipartimento di Sanit a Pubblica, Universit a degli Studi di Napoli Federico II, via Sergio Pansini 5, 80131 Napoli, Italia. E-mail: giancarlo.troncone@unina.it Received 29 March 2013; revised 27 January 2014; Accepted 18 March 2014 DOI: 10.1002/dc.23163 Published online 28 March 2014 in Wiley Online Library (wileyonlinelibrary.com).