Acoustic prism causing sonographic duplication artifact in the upper abdomen.

A variable prism of fat frequently occurs in the anterior abdominal wall that can produce confusing double-image artifacts on sonograms. This artifact is seen most frequently in the pelvis but is also seen in the upper abdomen, and is related to anatomic variations and the size of some ultrasound transducers. Phantom studies and a review of the CT scans of 100 patients were used to document the anatomy and frequency of occurrence of this variant.