Dr Dan J Bell and Radswiki et al.

Ascites is defined as an abnormal amount of intraperitoneal fluid.

Patients with a large volume of ascites can present with abdominal distension (which may be painful), nausea, vomiting, dyspnoea and peripheral oedema 7, 9.

Ascitic fluid is traditionally characterised as either:

  • transudate: thin, low protein count and low specific gravity
  • exudate: high protein count and specific gravity

More recently, the concept of the serum-ascites albumin gradient has been shown to be more accurate in the classification of the causes of ascites 5.  For the purposes of simplicity, however, we maintain the former classification.

Causes of transudative ascites:

Causes of exudative ascites:

Detection of intraperitoneal fluid on a plain radiograph requires at least 500 mL to be present.

Plain film findings of ascites include:

  • diffusely increased density of the abdomen
  • poor definition of the soft tissue shadows, such as the psoas muscles, liver and spleen
  • medial displacement of bowel and solid viscera (away from the properitoneal fat stripe)
  • bulging of the flanks
  • increased separation of small bowel loops

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

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 >15 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).

Medical management includes a modified diet (restricting sodium) and use of medications such as diuretics 7, 9. Interventional techniques for management include serial paracentesis (ascitic tap) , TIPS or peritoneovenous shunting 8, 9 .

Ascitic taps are the most common and thought to be the most effective treatment for symptomatic ascites 9. It can be performed with a variety of techniques depending on the institution and the availability of imaging resources 8:

  • blind: i.e. non-imaging guided
  • partially imaged-guided: an appropriate site is marked on the abdominal wall using ultrasound but the puncture is blind
  • imaging-guided: usually using ultrasound

Consider other causes of intraperitoneal fluid:

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Article information

rID: 12619
Synonyms or Alternate Spellings:
  • Ascitic fluid
  • Free intraperitoneal fluid

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Cases and figures

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    Case 1
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    Case 2: due to pancreatic duct fistula
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    Case 3: with cholangiocarcinoma
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    Case 4: with peritoneal carcinomatosis
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    Case 5: malignant ascites with omental disease
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    Case 6: with hepatic cirrhosis
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    Case 7: peritoneovenous shunt
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    Case 8: portal vein thrombosis and Crohn disease
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    Case 9: malignant ascites (ovarian)
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