Ascites

CT

CT is most sensitive to small amounts of fluid in the peritoneum which collects preferentially in the dependent regions, such as Morison pouch and the pelvis. The CT density of intraperitoneal fluid may give a clue to the underlying aetiology:

• transudative ascites density should be approximate to that of water (-10 to +10 HU)
• exudative ascites (density >5 HU)
• haemoperitoneum density is higher still (~45 HU)

Of course, other intra- or extra-abdominal CT features may give further evidence to the origin of the ascites (e.g. features of heart failure, features of cirrhosis, peritoneal catheter in situ, etc).

Ultrasound

May detect smaller volumes especially if it's adjacent to the diaphragm or anterior margin of the liver 3. Assessment of fluid type:

• simple ascites is anechoic
• exudative, haemorrhagic or neoplastic ascites contains floating debris
• septations suggest an inflammatory or neoplastic cause and may be called a loculated ascites

Reference