What is the role of ultrasonography in the workup of ascites?

Updated: Dec 29, 2017
  • Author: Rahil Shah, MD; Chief Editor: Praveen K Roy, MD, AGAF  more...
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Real-time ultrasonography is the easiest and most sensitive technique for the detection of ascitic fluid. Volumes as small as 5-10 mL can routinely be visualized. Uncomplicated ascites appears as a homogeneous, freely mobile, anechoic collection in the peritoneal cavity that demonstrates deep acoustic enhancement. Free ascites does not displace organs but typically situates itself between them, contouring to organ margins and demonstrating acute angles at the point at which the fluid borders the organ.

The smallest amounts of fluid tend to collect in the Morison pouch (posterior subhepatic space) and around the liver as a sonolucent band. With massive ascites, the small bowel loops have a characteristic polycyclic, "lollipop," or arcuate appearance because they are arrayed on either side of the vertically floating mesentery.

Certain ultrasonographic findings suggest that the ascites may be infected, inflammatory, or malignant. These findings include coarse internal echoes (blood), fine internal echoes (chyle), multiple septa (tuberculous peritonitis, pseudomyxoma peritonei), loculation or atypical fluid distribution, matting or clumping of bowel loops, and thickening of interfaces between fluid and adjacent structures. In malignant ascites, the bowel loops do not float freely but may be tethered along the posterior abdominal wall, plastered to the liver or other organs, or surrounded by loculated fluid collections.

Most patients (95%) with carcinomatous peritonitis have a gallbladder wall that is less than 3 mm thick. Mural thickening of the gallbladder is associated with benign ascites in 82% of cases. The thickening of the gallbladder is primarily a reflection of cirrhosis and portal hypertension.

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