Gastrointestinal Imaging

Ascites

effusion and accumulation of serous fluid in the peritoneal cavity. The main cause of ascites is liver cirrhosis associated with portal hypertension and with a lowered level of serum albumin. Other causes are portal hypertension of extrahepatic origin, cardiac failure, infectious peritonitis, peritoneal metastasis, ovarian tumours or myxoedema. In patients with these conditions the permeability of the subperitoneal capillaries is increased. Chylous ascites is due to obstruction of visceral lymphatic drainage or of the origin of the lymphatic duct at the level of the cisterna of Pecquet. On plain radiography of the abdomen, the features of intraperitoneal fluid are: an elevation of both diaphragms; a homogeneous shadow of soft tissue density, called "ground glass appearance", with poor visualization of the psoas line and the outline of the kidneys; obliteration of the right lateral inferior margin of the liver; and displacement of the ascending and descending colon medially with obliteration of the haustral markings and of the flank stripes. Hellmers sign refers to the visualization of a lateral lucent band between the lateral abdominal wall and the right liver lobe due to the interposition of fluid. On the left side a similar band of fluid may be interposed between the spleen and the lateral abdominal wall.

Smaller amounts of fluid will be detected first in the pelvis because it is the most dependent portion of the peritoneal cavity. The radiological signs indicating pelvic fluid are: obliteration of the fat line at the superior border of the bladder; a linear lucency between the fluid density and the bony pelvis caused by pelvic fat; and a symmetric density on both sides of the bladder called "dogs ears" which is due to the accumulation of fluid in the pelvic peritoneal recesses.

On barium study one can see the separation of small bowel loops by the interposed fluid if it is abundant. Sonographically free flowing intraperitoneal fluid is easily detected as hypoechoic structures in the hepatorenal fossa and in the paracolic gutters. With increasing ascites, fluid is also noted in the subhepatic and the subphrenic space and between the small bowel loops (Fig.1). Ultrasonography is also accurate in detecting fluid in the pelvis using the full bladder technique. However, small fluid collections within the pelvis are more clearly demonstrated on ultrasound with a transvaginal rather than a transabdominal approach. In loculated ascites, secondary to peritonitis, prior surgery or peritoneal metastasis, the bowel loops will not float in the central abdomen as they do in free ascites. Hyperechoic reflections may be noted on ultrasound if septations, debris or malignant seeding is present. CT (Fig.2) shows ascites as an extravisceral collection of fluid with an attenuation value less than that of adjacent soft tissue organs. In general CT will not only detect ascites but may in addition reveal the underlying cause in some instances.

ALB

To view high resolution images,
please register first.

Click  here to register.

Already registered? Enter your e-mail in the window below.
Re-register

Fig.1

Ascites. Ultrasound examination of the abdomen. a. There is a hypoechoic fluid collection in front of the spleen (S). b. The ascitic fluid is separating the small bowel loops and their mesenteric attachment.
Ascites, Fig.1 (a)
Ascites, Fig.1 (b)
Ascites, Fig.2