How is simple ascites distinguished from complicated ascites?
A. Watery transudate is usually caused by major organ failure (e.g., hepatic, renal, or cardiac).
B. CT density is similar to water (0-20 HU); HU is higher as the fluid protein content increases.
US: Simple ascites is anechoic, with increased through transmission and no internal septations. Ascites is “free-flowing” and located in the dependent portions of the abdomen and pelvis (i.e., Morison’s pouch, paracolic gutters, and pelvis). US demonstrates a sharp, smooth interface with other intraabdominal contents. Bowel seems to “float” within the fluid, usually in the center of the abdomen, if large amounts of ascites are present.
Loculated ascites is formed by adhesions, either benign (i.e., prior surgery), infectious, or malignant in etiologic origin. Loculated ascites is typically (1) nondependent, (2) stable when patient changes position, and (3) may displace adjacent bowel loops.
Complex ascites is usually secondary to an infectious, hemorrhagic, or neoplastic process. Findings include internal debris or septations, a thick or nodular border or capsule, and HU of more than 20. Aspiration may be required to determine whether a collection is simple or complex.