What imaging studies are recommended for diagnosing ascites (accumulation of fluid in the peritoneal cavity)?

From the Guidelines

For ascites, abdominal Doppler ultrasound should be obtained as the initial imaging study, as it is non-invasive, readily available, and can detect as little as 100mL of ascitic fluid while also evaluating the liver for cirrhosis, masses, and portal hypertension 1.

Key Points to Consider

• The initial evaluation of ascites should include history, physical examination, abdominal Doppler ultrasound, laboratory assessment of liver and renal function, serum and urine electrolytes, and a diagnostic paracentesis for analysis of the ascitic fluid 1.
• Abdominal Doppler ultrasound is the preferred initial test due to its safety, cost-effectiveness, and ability to guide paracentesis.
• Additional imaging modalities such as CT scan with contrast or MRI may be necessary based on initial findings and clinical presentation, especially if malignancy or other non-cirrhotic causes of ascites are suspected.

Imaging Modalities

• Abdominal Doppler ultrasound: initial test of choice, non-invasive, readily available, and can detect small amounts of ascitic fluid.
• CT scan with contrast: provides more detailed information about the liver parenchyma, potential malignancies, and can better characterize the extent and distribution of ascites.
• MRI: may be used when more detailed tissue characterization is needed, particularly for evaluating liver lesions or when CT is contraindicated.

Clinical Considerations

• Diagnostic paracentesis should be performed in all patients with new-onset Grade 2 or 3 ascites, and in all patients hospitalized for worsening ascites or any complication of cirrhosis 1.
• The serum-ascites albumin gradient (SAAG) should be calculated to differentiate ascites due to portal hypertension from other causes 1.

From the Research

Imaging Modalities for Ascites

To evaluate ascites, various imaging modalities can be employed, including:

• Ultrasound: a useful first-line imaging modality for clinical triage, capable of detecting small volumes of fluid and quantifying the volume of ascites 2
• Computed Tomography (CT): traditionally regarded as the imaging modality of choice to demonstrate ascites and diagnose the underlying cause, but may not be as effective as ultrasound in qualitative assessment of fluid 2
• Endoscopic Ultrasound (EUS): a sensitive and specific modality for determining peritoneal implants, particularly useful in patients with intra-abdominal malignancies 3
• Magnetic Resonance Imaging (MRI): may be used to evaluate ascites, but is not as commonly employed as ultrasound or CT

Specific Imaging Recommendations

For patients with ascites, the following images may be obtained:

• Ultrasound images to quantify the volume of ascites and assess the characteristics of the fluid 2
• CT scans to evaluate the underlying cause of ascites and detect any complications 4
• EUS images to determine peritoneal implants in patients with intra-abdominal malignancies 3

Diagnostic Evaluation

The diagnostic evaluation of ascites involves:

• Determining the serum-ascites albumin gradient to assess the cause of ascites 4
• Excluding complications such as spontaneous bacterial peritonitis 4
• Employing a systematic approach to attempt to provide an underlying diagnosis once ascites is detected on ultrasound 2