The lesser sac and gastrohepatic recess: sonographic appearance and differentiation of fluid collections.

The sonographic appearance and differentiation of fluid collections within the gastrohepatic recess and lesser sac are described. The identification of the lesser omentum and stomach is fundamental to their separation. Accurate localization of upper abdominal fluid may be of aid in selecting an appropriate approach for paracentesis as well as directing the subsequent diagnostic work-up.