Ascites

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 19/07/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 2557 times

 Free-flowing ascites conforms to shape of surrounding structures and flows to dependent recesses

image Simple fluid signal on T1WI (hypointense) and T2WI (hyperintense) MR
image No appreciable complexity within ascites fluid
• Exudative  ascites: Typically demonstrates increasing density of fluid with increasing protein content

image Often mildly hyperdense (15-30 HU) relative to transudative ascites
image May demonstrate complexity, including septations, peritoneal thickening/enhancement, and loculation
image Loculated ascites fluid exerts mass effect and displaces adjacent structures (such as bowel loops)
image Usually simple fluid signal on T1WI and T2WI MR, but internal complexity and protein can result in intermediate T1 and T2 signal
image Chylous ascites can measure < 0 HU or demonstrate fat-fluid levels

PATHOLOGY

• Ascites is typically divided into 2 types

image Transudative ascites is caused by high portal venous pressures and is characterized by low protein, low LDH, normal glucose, and low specific gravity

– Transudative ascites is simple ascites fluid most often caused by cirrhosis, hepatitis, heart failure, renal failure, hypoproteinemia, etc.
image Exudative ascites is characterized by high protein and high specific gravity 

– Exudative ascites related to multiple causes, such as infection, ischemia, peritoneal carcinomatosis, peritonitis, or pancreatitis
image
(Left) Axial CECT shows ascites image due to hepatic cirrhosis, with large varices and splenomegaly. Notice the relatively simple, uncomplicated appearance of this transudative ascites.

image
(Right) Axial CECT shows massive ascites due to right heart failure. Like other forms of transudative ascites, note that the fluid appears simple without evidence of complexity, nodularity, or adjacent peritoneal thickening/enhancement.
image
(Left) Ultrasound shows large anechoic ascites image in the lower abdomen displacing bowel loops image in a patient with cirrhosis. As in this case, simple transudative ascites is classically anechoic, freely mobile, and shows acoustic enhancement.

image
(Right) Ultrasound shows complicated ascites image in a cirrhotic patient. The fluid was non-mobile and loculated on real-time scanning, and there are multiple internal septations image, suggesting this is not simple transudative ascites. The ascites fluid was found to be infected.

TERMINOLOGY

Definitions

• Pathologic accumulation of fluid within peritoneal cavity

IMAGING

General Features

• Best diagnostic clue

image Diagnostic paracentesis (in cases where either infection or tumor is suspected)
• Location

image Free-flowing ascites fluid flows to most dependent recesses of abdomen and pelvis

– Morison pouch (hepatorenal fossa): Most dependent recess in upper abdomen
– Rectouterine or rectovesical space: Most dependent spaces in pelvis
– Paracolic gutters and subphrenic spaces
– Lesser sac usually does not fill with ascites, with the exception of cases with tense ascites or ascites due to a local source (gastric ulcer or pancreatitis)

image Otherwise, lesser sac fluid suspicious for ascites related to carcinomatosis or infection
• Morphology

image Free-flowing ascites: Conforms to shape of surrounding structures and does not deform normal shape of adjacent organs or exert mass effect

– Fluid insinuates itself between organs
image Loculated fluid: Fluid demonstrates rounded contour and appears encapsulated

– Loculated ascites fluid exerts mass effect and displaces adjacent structures (such as bowel loops)
• Key concepts and descriptors

image Ascites typically divided into 2 types

– Transudative ascites is caused by high portal venous pressures and is characterized by low protein, low LDH, normal glucose, and low specific gravity

image Transudative ascites is simple ascites fluid that is most often caused by cirrhosis, hepatitis, heart failure, renal failure, or hypoproteinemia
– Exudative ascites characterized by high protein and high specific gravity

image Exudative ascites related to multiple causes, such as infection, ischemia, peritoneal carcinomatosis, peritonitis, and pancreatitis
image Transudate, exudate, hemorrhagic, pus
image Chylous, bile, pancreatic, urine, cerebrospinal fluid
image Pseudomyxoma peritonei, neonatal ascites

Radiographic Findings

• Abdominal radiograph: Insensitive for fluid, as diagnosis of ascites on radiographs requires a substantial amount of fluid to be present (usually > 500 cc)

image Diffuse haziness and increased density of abdomen
image Poor visualization of normally visualized soft tissue structures, such as psoas and renal outline

– Obliteration of hepatic and splenic angles
image Bulging of flanks due to fluid distending abdomen
image Separation of small bowel loops with centralization of floating gas-containing small bowel
image Hellmer sign: Lateral edge of liver medially displaced from adjacent thoracoabdominal wall
image Symmetric densities on sides of bladder (dog ears sign)
image Medial displacement of ascending and descending colon
image Lateral displacement of properitoneal fat line

CT Findings

• Transudative ascites

image Typical transudative ascites has density of 0-15 Hounsfield units (HU) and appears free flowing
image Small amounts of ascites typically seen in right perihepatic space, Morison pouch, and pouch of Douglas
image Larger amounts of fluid accumulate in paracolic gutters

– Ascites can cause centralization of bowel loops
– Ascites accumulating in central abdomen may have triangular configuration within leaves of mesentery
image Massive ascites distends peritoneal spaces
image Look for associated evidence of liver, heart, or kidney failure (most common causes of transudative ascites)
• Exudative ascites

image Exudative ascites typically demonstrates increasing density of fluid with increasing protein content

– Exudative ascites often mildly hyperdense relative to transudative ascites (15-30 HU)
– May demonstrate complexity, including septations, peritoneal thickening/enhancement, and loculation
image Ascites related to peritoneal carcinomatosis: Complex ascites with nodularity and thickening of adjacent peritoneum and frequent loculation of ascites

Buy Membership for Radiology Category to continue reading. Learn more here