Distinguishing a Pancreatic Pseudocyst from a Mucinous Cystic Neoplasm
In the March issue of Gastroenterology, Katie Connor et al describe a 22-year-old woman who came to the hospital because of a 2-month history of epigastric discomfort. Three months before, she received an electric shock that caused her to fall onto her abdomen. This caused some epigastric pain at the time, but she did not go to the hospital until 3 months later. Otherwise, she had no history of medical treatment or surgery, and she was a nonsmoker who drank alcohol only occasionally. Physical examination revealed that she was healthy with the only notable finding of a palpable epigastric mass that was mildly tender on palpation.
Analyses of blood counts, urea, electrolytes, glucose, and liver function produced normal results. However, a contrast-enhance computed tomography scan of the abdomen revealed low-viscosity, clear, cystic fluid (see figure).
The large, unilocular, cystic mass originated from the tail of the pancreas with an absence of septations, mural nodules, or cystic calcifications.
Imaging, clinical history, and analysis of the cystic fluid led to a diagnosis of pancreatic pseudocyst. However, biopsy analysis of the cyst wall revealed a benign mucus-producing columnar epithelium with areas positive for estrogen receptor—consistent with a benign mucinous cystic neoplasm (MCN). Connor et al performed a distal pancreatectomy and the patient’s recovery was uncomplicated.
Given the established malignant potential of MCNs (6%-27% of cases), the authors state that performing cystgastrostomy for pseudocyst, as planned, could have allowed the cyst to become malignant.
The authors explain that pancreatic cystic neoplasms are rare and accurate diagnosis requires a high index of suspicion. It can be a challenge to distiguish a unilocular neoplasm without mural thrombi or eggshell calcifications from a pseudocyst.
MCAs typically contain viscous mucin-rich fluid, with low amylase content; unlike pseudocysts, there is usually no communication with the pancreatic ducts. Measurements of CA19-9 and carcinoembryonic antigen can be informative. It is unclear is whether preoperative endoscopic ultrasonography, with or without contrast enhancement or magnetic resonance cholangiopancreatography, would have revealed that the patient had a benign MCN.
In a study of 1 specialist center, 20.3% of MCNs were found to be misdiagnosed—12% of the misdiagnosed MCNs were pseudocysts. Only cyst wall biopsy analysis revealed that this patient had MCN. Connor et al therefore recommend multiple biopsies from different areas, because foci of malignant transformation can be missed, and tissues can be collected from areas of de-epithelialization (which mimick a pseudocyst).
Increasing use of minimally invasive drainage of pancreatic pseudocysts could reduce the ability to obtain representative biopsies. Many centers continue to manage pseudocysts without routine access to magnetic resonance imaging or advanced endoscopy—it is important to emphasize the need for biopsy analysis in these situations. Connor et al state that cost-effective guidelines are required to avoid further near misses of pancreatic cystic neoplasms.