Pseudoenhancement of Gallbladder Sludge: A Confusing Artifact Caused by Nonlinear Propagation of Ultrasound Through Microbubbles

Introduction

Gallbladder sludge is a mixture of particulate matter and bile that occurs when the solutes in bile precipitate. Sometimes, motionless gallbladder sludge mimics a gallbladder polyp or cancer on transabdominal ultrasonography. Previous studies demonstrated that contrast-enhanced ultrasonography (CEUS) is useful for differentiating biliary sludge from other polypoid gallbladder lesions by an experienced radiologist, with a sensitivity of 100 % (Xie XH et al. Eur Radiol 2010; 20: 239 – 248).

CEUS is extremely sensitive in detecting microbubbles within viable vascular tissue. Because biliary sludge lacks vessels, the absence of enhancement allows differentiation from tumors, which enhance in almost all cases (Piscaglia et al. Ultraschall in Med 2012; 33: 33 – 59). However, an unexpected case was encountered when we used CEUS to assess a mass-like lesion in the gallbladder. Apparent enhancement was detected within the sludge that was later confirmed by pathological examination. A phantom experiment in vitro was performed to reproduce and analyze the pseudoenhancement.