Abnormal accumulation of fluid within peritoneal cavity

Free-flowing fluid insinuates itself between organs & is shaped by surrounding structures

Fluid collects in most dependent locations, such as pouch of Douglas, Morison pouch, & bilateral flanks, unless there are loculations

Ultrasound accurate at detecting, localizing, & characterizing ascites; quantification more subjective

Simple: Anechoic; homogeneous, freely mobile, deep acoustic enhancement

Complicated: Echogenic fluid with coarse or fine internal echoes, layering debris or particulate material, septa

Small free fluid in cul-de-sac is physiologic in women

Look for associated hepatic disease, peritoneal masses, or adherent bowel

Hemoperitoneum

Malignant ascites

Peritoneal inclusion cyst

Pseudomyxoma peritonei

Large cyst (ovarian, mesenteric)

Other fluids, such as bile, urine

Phsyiologic free fluid

Most common causes: Acute & chronic liver disease, heart & kidney failure, pancreatitis, nephrotic syndrome, cancer

Paracentesis is required for protein content, cell count, culture, & cytology

Soft tissue nodules along peritoneal surfaces suggest tumor

Peritoneal thickening suggests tumor or infection