Focal periportal sparing in hepatic fatty infiltration: a cause of hepatic pseudomass on US.

An unusual pattern of hepatic fatty infiltration was detected sonographically in 31 patients over a 1.5-year period. At appropriate gain settings and time gain compensation, the liver parenchyma demonstrated diffuse increased echogenicity except for a solitary hypoechoic area with relatively distinct margins, usually located in the medial segment of the left hepatic lobe. This hypoechoic periportal focus varied in size between 1.5 and 5 cm and was typically ovoid, but was occasionally spherical or irregular in shape. Eight patients with such foci underwent percutaneous needle biopsy because of concern that there was a space-occupying mass. Microscopic examination of specimens from the hypoechoic periportal region revealed normal hepatic parenchymal cells, while tissue samples from the surrounding liver had high fat levels. In the remaining 23 patients, correlative radiologic studies supported the diagnosis of fatty liver and excluded a central-mass lesion. A localized area of normal hepatic tissue should be considered among the possible diagnoses when a circumscribed hypoechoic periportal area is demonstrated within a fatty liver.