Ascariasis is the commonest helminthic infection worldwide and estimated to affect nearly 1 billion people (25% of the population). The disease is transmitted by Ascaris lumbricoides which belongs to the nematode family (roundworms).
Infection occurs by ingestion of contaminated food (faeco-oral route), the swallowed eggs hatch in the intestine giving rise to the larvae which penetrate the intestinal mucosa and travel through the blood and lymphatics to the liver and lung. In the lung, they maturate to form adult worms which then migrate through the airways to the larynx and pharynx and are re-swallowed into the stomach as adult worms. They may remain in the intestinal lumen or penetrate the duodenal mucosa to pass into the CBD.
The infected patients are usually asymptomatic, however, migration through the lung may cause eosinophilic pneumonia. Moreover, the adult worms cause mechanical obstruction to the intestinal lumen or may penetrate and obstruct the common bile duct leading to obstructive jaundice (Courvoisier sign if painless).
The adult worm can appear as a longitudinal or curved filling defect within the intestinal lumen during a contrast follow through study.
Identification of the long hyperechoic structure within the liver with hypoechoic center is highly suggestive.
Dilated CBD harbors a long curved hyperdense structure with central hypodensity. Within the intestine, they appear as a filling defect within the contrast in the lumen.
Best non-invasive method to detect biliary ascariasis. The worm appears as a hypointense structure within the hyperintense CBD. With 3T MRI identification of the "three line sign" in thick slab MRCP confirms the diagnosis.
Gold standard but an invasive method. It is used also in the extraction of CBD worms.
Adult worms may cause CBD obstruction and recurrent cholangitis. Also, they may aggregate within the intestinal lumen forming a mass and cause intestinal obstruction.
Endoscopic removal of CBD worms should be done under the umbrella of antihelminthic therapy.
- 1. Alper F, Kantarci M, Bozkurt M et-al. Clinical Radiology. 2003;58 (11): . doi:10.1016/S0009-9260(03)00291-5
- 2. Ding ZX, Yuan JH, Chong V et-al. 3 T MR cholangiopancreatography appearances of biliary ascariasis. Clin Radiol. 2011;66 (3): 275-7. doi:10.1016/j.crad.2010.11.004 - Pubmed citation
- 3. Sinha R, Rajesh A, Rawat S et-al. Infections and infestations of the gastrointestinal tract. Part 2: parasitic and other infections. Clin Radiol. 2012;67 (5): 495-504. doi:10.1016/j.crad.2011.10.022 - Pubmed citation