Displaced retroperitoneal fat: sonographic guide to right upper quadrant mass localization.

While it is often easy to detect masses in the right upper quadrant that originate from the liver, adrenal gland, or kidney, it may be difficult to determine the anatomic origin of large masses in the posterior aspect of the right upper quadrant. In this paper it is reported that the reflection produced by right upper quadrant retroperitoneal fat is displaced in a characteristic manner by masses originating in this area. This greatly assists in the localization of these masses. Hepatic and subhepatic masses posteriorly displace this echo, while renal and adrenal lesions anteriorly displace it.