title: Ultrasonographic demonstration of inner tube sign: a tropical dilemma.
abstract: BACKGROUND
  Ultrasonographic demonstration of intra biliary parallel lines or "inner tube sign" is considered diagnostic for biliary ascariasis in regions where ascariasis is endemic.
  
  
  METHODS
  148 patients with inner tube sign on ultrasonography were evaluated. In most, diagnosis was confirmed by ultrasonographic demonstration of restitution of normal appearance of bile duct with passage of round worms in vomitus or faeces.
  
  
  RESULTS
  Diagnosis was confirmed in 122 of 148 patients. 26 patients were lost to follow-up. Biliary ascariasis was responsible for the sign "parallel lines" in 113 patients. Of the remaining, intrabiliary stents were responsible for the "inner tube sign" in six whereas in three it was due to hydatid membranes following intrabiliary rupture of hydatid cyst.
  
  
  CONCLUSIONS
  Biliary ascariasis is the commonest cause of inner tube sign in the tropics. However, this sign can also be produced by biliary stents and hydatid membranes. Awareness of these possibilities is essential for sonologists in the tropics.
authors.forename: Shivaram Prasad
authors.initials: SP
authors.lastname: Singh
authors.forename: Debasis
authors.initials: D
authors.lastname: Misra
authors.forename: Mihir Kumar
authors.initials: MK
authors.lastname: Mohapatra
authors.forename: Omprakash
authors.initials: O
authors.lastname: Agrawal
authors.forename: Chudamani
authors.initials: C
authors.lastname: Meher
mesh_terms: D000293:Adolescent; D001196:Ascariasis / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000473:pathology; D002648:Child; D015331:Cohort Studies; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D014330:Tropical Medicine / Q000379:methods; D014463:Ultrasonography