Role of Ultrasound in Ascites: Detection, Characterization, and Evaluation of the Underlying Cause.

Normally, the peritoneal cavity contains 25-50 mL of ascitic fluid, which allows for the movement of bowel loops past one other and helps hydrate serosal surfaces. Ascites is defined as the pathological accumulation of excess fluid in the peritoneal cavity.

More than one cause may be responsible for the development of ascites (multifactorial), liver cirrhosis remains the leading cause (≈85% of cases), followed by many causes such as malignant neoplasia, tuberculous infection, cardiac insufficiency, renal diseases ,trauma and other infectious, inflammatory and hemorrhagic causes ,multiple etiologies may coexist.

once ascites develops, it carries a risk of further serious complications such as acute spontaneous bacterial peritonitis (SBP) (Occurs in 10-30% of hospitalized cirrhotic patients with ascites and associated with high morbidity and mortality rate), hepatorenal syndrome, hepatic hydrothorax, respiratory compromise and other compliactions including gastrointestinal, circulatory , metabolic complications….etc Medical history, physical examination, abdominal ultrasound, blood tests, and a diagnostic paracentesis for ascitic fluid analysis should all be part of the initial assessment of ascites. Ascites can be detected on physical examination using traditional shifting dullness to percussion when there is approximately 500 ml of fluid. However, in an increasingly obese population, there is limited reliability on clinical examination findings alone.

Trans-abdominal US (TAUS) can easily demonstrate large volumes of fluid and, with a meticulous technique, much smaller volumes can also be detected making an excellent first-line imaging tool, safe, inexpensive, and widely available, It's also superior to CT in qualitative assessment-distinguishing between simple (anechoic) and complex (particulate or septated) ascites.Portable ultrasound devices further enable reliable, bedside diagnosis.

Ultrasound is also used in ultrasound-guided aspiration and paracentesis which is essential for safely obtaining ascitic fluid for determining the underlying etiology (via Serum-Ascites Albumin Gradient (SAAG), cytology, biochemical analysis) and detecting complications such as spontaneous bacterial peritonitis,The presence of septations or debris in ascites fluid can be suggestive of infected ascites.