The inner tube sign in Ascariasis

Excerpt

Two echogenic lines that represent the roundworm’s alimentary tract, seen inside and parallel to the two outer echogenic walls of the worm (arrow in Fig. 1 and Video 1 in Supplementary material), constitutes the “inner tube sign” on ultrasound [1]. Thus, longitudinal section of the worm on the ultrasound gives this characteristic tube within a tube appearance. Analogous to this appearance may be appreciated in the barium examinations when the barium ingested by the worm outlines its alimentary tract as a dense line. Ascaris lumbricoides, a nematode, is one of the largest and most common roundworms affecting human small intestine. Sonographic features of adult roundworm are well recognized that include linear or curvilinear, mobile or non-mobile, non-shadowing long echogenic strip with central anechoic area [2] seen within the small bowel or biliary system. A “target appearance” or “bull’s eye” sign may be appreciated on ultrasound with axial orientation of the probe, especially when the worm is in the biliary tract [3]. Contrast-enhanced computed tomography of the same patient also revealed the worm as a curvilinear hypodense structure (Fig. 2), within the fluid-filled lumen of the jejunum.

…