Focal Sparing

                 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.
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This is radiology images of Metastatic breast carcinoma in a fatty liver. Multiple nodules are scattered throughout a heterogeneous, poorly enhancing liver.
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