The medical term for abnormal accumulation of fluid in the abdominal cavity is ascites.
Ascites is fluid buildup within the peritoneal cavity, the space surrounding many abdominal organs. The fluid can enlarge the abdomen, cause a sensation of pressure or heaviness, and sometimes make breathing difficult by pressing upward against the diaphragm. Small amounts may be detected only with ultrasound, while severe cases can produce marked abdominal distension.
In developed countries, cirrhosis of the liver is the most common cause. Scarring and portal hypertension alter blood flow and pressure in the abdominal circulation, encouraging fluid to leave blood vessels and collect around the organs. Cancer, heart failure, pancreatitis, tuberculosis, and hepatic-vein obstruction can also cause ascites.
Ascites should not be confused with edema, which is fluid accumulation in body tissues, or pleural effusion, which is fluid around the lungs. Peritonitis is inflammation or infection of the abdominal lining and can occur as a dangerous complication called spontaneous bacterial peritonitis. Doctors may analyze ascitic fluid after paracentesis to identify its cause.