Tube within tube: Ascaris in bowel and biliary-tract.

Ascaris lumbricoides is one of the most common human helminthic diseases worldwide. On ultrasound, it is seen as linear non-shadowing echogenic structures with target appearance in cross section, and the live worm may show writhing movements in real time. On barium meal follow through, it appears as radiolucent tubular filling defects within the bowel lumen. Though not sensitive, direct real-time visualization of Ascaris on ultrasound is quick, non-invasive, and definitive.