Focal sparing

Newman, J.S., Oates, E., Arora, S., Kaplan, M. Focal spared area in fatty liver simulating a mass. Scintigraphic evaluation. Dig. Dis. Sci. 1991 36 1019-1022... 

Arai K, Matsui O, Takashima T, et al (1988) Focal spared areas in fatty liver caused by regional decreased portal flow. AJR Am J Roentgenol 151 300-302... 

Arita T, Matsunaga N, Homma Y, et al (1996) Focally spared area of fatty liver caused by arterioportal shunt. J Comput Assist Tomogr 20 360-362... 

Tochio H, Kudo M, Okabe Y, et al (1999) Association between a focal spared area in the fatty liver and intrahepatic efferent blood flow from the gallbladder wall evaluation with color Doppler sonography. AJR Am J Roentgenol 172 1249-1253... 

Zhang, Z. G., Chopp, M., Gautam, S., Zaloga, C., Zhang, R. L., Schmidt, H. H. H. W., Pollock,]. S., and Forstermann, U. (1994). Upregulation of neuronal nitric oxide synthase and mRNA, and selective sparing of nitric oxide synthase-containing neurons after focal cerebral ischemia in rat. Brain Res. 654, 85-95. 

Lesions that contain haemodynamically normal liver fill in the same way as the normal surrounding tissue and so tend to disappear in this late phase. Examples include focal fatty sparing/change, regenerating nodules in cirrhosis and focal nodular hyperplasia in which the central scar is often seen as a stellate defect at this stage (Fig. 1.6). The arterial phase is useful for characterising lesions based on their blood supply hypervascular lesions such as hepatocellular... 

Focal fatty sparing Focal fatty change... 

Focal fatty changes and focal fatty sparing usually are believed to correspond respectively to areas with fatty infiltration in a normal liver or areas preserved from fatty deposition in a steatotic liver. However, the division appears not so clear cut in all cases, since often the different appearance at imaging techniques, and particularly at ultrasound, seems rather to correspond to a similar quantity of deposited fat, but contained in fewer droplets within the pseudotumor (when it appears "hypoechoic ) or in larger numbers of fat-filled vacuoles with respect to that of the surrounding parenchyma ( hyperechoic lesions or fatty changes) (Caturelli et al. 1991). 

Focal Fatty Infiltration and Focal Fatty Sparing 160 References 165... 

Fig. 11.16a,b. Obese patient with low hepatic attenuation consistent with diffuse steatosis. Areas of focal fatty sparing displaying normal attenuation values are recognized at the posterior aspect of segment IV (a) and adjacent to the gallbladder fossa (b)... 

Doppler typically shows no or some peripheral vascularity in hypovascular metastases, while hy-pervascular deposits may show vessels throughout the lesion (Fig. 18.1). Use of Doppler can be useful to differentiate metastases from FNH and focal fatty change/infiltration large FNH (>approx. 4 cm) often shows a typical spoke-wheel arterial pattern, often within a central scar (Fig. 18.1) focal fatty change/sparing shows no abnormal vascularity and normal hepatic vessels crossing the lesion with no deviation. 

Focal fatty change and focal fatty sparing show the same contrast behaviour as normal liver parenchyma in all phases, since they contain no abnormal vessels and essentially consist of normal parenchyma. Again, these lesions usually disappear after contrast injection (Fig. 18.11). 

Fig. 18.11a,b. Focal fatty sparing near the gallbladder in a patient with pharyngeal carcinoma, a Unenhanced US shows a round hypoechoic lesion suggestive of a metastasis (arrow), b Homogeneous enhancement of the lesion in the delayed phase post SonoVue. The lesion is iso-enhancing compared to normal liver it has disappeared ... 

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