The string sign for diagnosis of mucinous pancreatic cysts

Pancreas cyst fluid analysis does not provide optimal discrimination between mucinous and nonmucinous cysts. The aim of this study was to assess the performance characteristics of the "string sign" - a test performed at the time of endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA), for the diagnosis of mucinous pancreatic cysts (branch duct intraductal papillary mucinous neoplasms [bIPMN] and mucinous cystic neoplasms).

Patients undergoing EUS-FNA of pancreatic cystic lesions at one referral center between 2003 and 2012 were included. The string sign was performed prospectively, and was considered positive if ≥ 1 cm string formed in cyst fluid and lasted for ≥ 1 second. Performance characteristics of the string sign and a sequential cyst fluid test interpretation model were assessed.

For 98 histologically proven cases, the sensitivity, specificity, positive predictive value, and negative predictive value of the string sign for diagnosis of mucinous cysts were 58 % (95 % confidence interval [CI] 44 % - 70 %), 95 % (83 % - 99 %), 94 % (81 % - 99 %), and 60 % (46 % - 72 %), respectively. When string sign results and carcinoembryonic antigen (CEA) concentration (≥ 200 ng/mL) were combined, diagnostic accuracy improved from 74 % and 83 %, respectively, to 89 % (P ≤ 0.03). Among bIPMN, a positive string sign was associated with gastric and intestinal epithelial subtypes. The sequential cyst fluid test interpretation model (including cytology, mucin stain, CEA, and string sign) yielded an overall sensitivity for mucinous lesions of 96 %, with a specificity of 90 %.

The string sign is highly specific for diagnosis of mucinous pancreatic cysts, and improves overall diagnostic accuracy of pancreatic cyst fluid analysis. Sequential cyst fluid test interpretation yields high diagnostic sensitivity and specificity for mucinous cysts.