History :  A 71-year-old male with abdominal distension

What is the abnormality?

A. Negative study
B. Abdominal mass
C. Ascites
D. Small bowel obstruction

C. Ascites

* Abdominal X-rays should not be used to check for ascites.

* If this diagnosis is suspected then again ultrasound is the best initial investigation, and can also be used to assist drainage.

* Fluid and soft tissues have similar densities, and so ascites may be mistaken for organomegaly.

Key points

• Free fluid and solid organs have similar densities
• In the presence of ascites gas within bowel is located centrally

Plain film:

* Detection of intraperitoneal fluid on plain film requires at least 500 ml

* Plain film findings of ascites include:

• Diffusely increased density of the abdomen
• Poor definition of the the soft tissue shadows, such as the psoas muscles, liver and spleen
• Medial displacement of bowel and solid viscera (away from properitoneal fat stripe)
• Bulging of the flanks
• Increased separation of small bowel loops

space between properitoneal fat line and the colon more than 5 mm

Pathology :

* Ascitic fluid :

• 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 classification of the causes of ascites.

Causes of transudative ascites

• Hepatic cirrhosis
• Alcoholic hepatitis
• Heart failure
• Hypoproteinaemia
• Portal vein thrombosis
• Peritoneal dialysis
• Malignancy  : most commonly: breast, ovarian, endometrial, gastrointestinal and pancreatic

Causes of exudative ascites

• Peritoneal carcinomatosis
• Pancreatitis
• Abscess
• Nephrotic syndrome
• Peritonitis, e.g. tuberculosis
• Ischaemic bowel
• Bowel obstruction