CT Abdoment with contrast for MetastaticFatty Liver (Steatosis) Clinical
Fatty infiltration (steatosis) ranges from diffuse to focal. Drugs associated with steatosis include tetracycline and tamoxifen (used for adjuvant hormone therapy for breast cancer). Fatty liver develops in a setting of heterozygous hypobetalipoproteinemia, and this entity should be considered as a possible cause.Conditions associated with fatty liver infiltration.
- Diabetes mellitus
- Cystic fibrosis
- Fatty liver of pregnancy
- Total parenteral nutrition
- Familial heterozygous hypobetalipoproteinemia
- Metabolic liver disorders
-Glycogen storage diseases
of an unexplained fatty liver. Acute fatty liver in pregnancy is discussed in a separate section. Mild hepatic iron overload develops in some patients with nonalcoholic steatohepatitis,
possibly due to the concomitant presence of the hemochromatosis gene mutation; homozygous or heterozygous mutations of this geneare common in patients with nonalcoholic steatohepatitis.
A minority of patients receiving intraperitoneal insulin during peritoneal dialysis develop subcapsular steatosis, seen with CT as subcapsular hypodense nodules or rindlike regions Steatosis generally improves once a known inciting agent is removed Diffuse Steatosis Both CT and US provide qualitative rather than quantitative evidence of liver fat. Precontrast CT suggests steatosis if liver attenuation is
less than the spleen; typical criteria for steatosis consist of liver attenuation 10 HU less than spleen or a liver-to-spleen ratio of <0.9. Postcontrast, the spleen is not an accurate reference standard; muscle tissue is an adequate standard only if fatty infiltration is pronounced. Contrastenhanced CT in fatty infiltration reveals normal vessels coursing through fat, rather than being displaced as is often the case with a neoplasm.Ultrasonography of diffuse fatty infiltration reveals a hyperechoic pattern throughout the liver, to the point of masking the normally hyperechoic portal vein wall. Kidneys have been used as a standard to establish liver echogenicity. The hepatorenal echo intensity difference is greater in fatty livers than in normal livers; a hepatorenal difference of >7 dB is a sensitive
indicator of a fatty liver.
Because a normal pancreas is slightly more hyperechoic than a normal liver, it too is a useful landmark to detect increases in liver echogenicity.Magnetic resonance spectroscopy measures the lipid volume fraction in liver steatosis. Spinecho (SE) sequences are relatively insensitive in detecting fatty infiltration. Chemical shift imaging using in-phase and opposed-phase SGE sequences distinguishes proton signals from water and fat. Imaging with fat and water protons in-phase results in their signals being additive, while opposed-phase imaging leads ment pattern.
Focal Fatty Infiltration
Pathogenesis of focal fatty infiltration is not clear. Focal infiltration has a predilection for sites close to the falciform ligament and adjacent to gallbladder fossa. An anomalous portal venous supply, such as aberrant gastric venous drainage, is associated with focal fatty infiltrations. The importance of different insulin levels in an aberrant portal vessel as an inductor of steatosis is conjecture.
Focal fatty infiltration is segmental and often wedge-shaped in appearance; it should not be spherical in outline. As the term suggests, fat infiltrates and should not displace vessels.
Rarely, focal involvement appears as multiple small lesions mimicking metastases or abscesses. Some focal infarcts have a similar appearance.
Ultrasonography of focal fatty infiltration
shows a normal liver parenchyma containing fatty hyperechoic regions.The MRI typically reveals a wedge-shaped region, hyperintense on T1-weighted images and extending to the periphery. Magnetic resonance imaging appearance is not pathognomonic; an intrahepatic cholangiocarcinoma can have a similar appearance. Post-ferumoxides,fatty infiltration is relatively high in intensity in all on T1-weighted images, with these regions ranging from hyper- to isointense on T2-weighted images.
Kupffer cells tend to be present in fatty infiltration, evidenced by Tc-99m–sulfur colloid uptake. A minority of focal fatty infiltrations,LIVER however, has no colloid uptake and the appearance mimics a metastasis.
Focal regions of sparing are found in some patients with generalized fatty infiltration.Diffuse fatty infiltration with focal sparing tends to be segmental, with sparing having a predilection for segment IV and specific sites, such as subcapsular, close to the porta hepatis, and adjacent to the interlobar fissure. Efferent gallbladder blood flow plays a role in focal sparing at the gallbladder fossa. Doppler US reveals blood flow from the gallbladder in many patients with adjacent focal sparing. Thus focal sparing depends to some degree on whether the gallbladder is intact or not. In patients with fatty infiltration, gray-scale US detected focal sparing more often in patients with an intact gallbladder than in those with a prior cholecystectomy.
An association exists between sparing along the posterior edge of segment IV and aberrant gastric venous drainage to this segment. A focal decrease in portal blood flow to this segment is the most likely cause of such sparing. Focal sparing of a fatty liver develops in a setting of an arterioportal shunt, presumably due to a decrease in portal blood flow.
Focal sparing is hyperdense both with preand postcontrast CT and appears as a hypoechoic focus with US. Difficulty arises in a fatty liver in differentiating focal sparing from neoplasms.An occasional metastasis can appear as a wedge-shaped hyperdense region on nonenhanced CT, similar to focal sparing in a fatty liver, due to focal intrahepatic portal vein obstruction.
Regions of focal sparing, representing normal liver containing reticuloendothelial cells, take up the SPIO contrast agent ferumoxides. Focal sparing thus reveals a signal loss and has a low intensity on T1- and T2-weighted images.
Liver metastases appear to be less common in patients with a fatty liver than in a normal liver.When present, their appearance is modified by the underlying fat as CT Abdoment with contrast in under:
CT Abdoment with contrast axial crosectional in Metastatic breast carcinoma in a fatty liver. Multiple nodules are scattered throughout a heterogeneous, poorlyenhancing liver. (Courtesy of Patrick Fultz, M.D., University of Rochester.)