Fig. 4.

Example of intra-ductal factors causing potential pitfalls in interpretation. a Axial T2-weighted MRI shows an air-fluid level in a dilated proximal CBD in keeping with aerobilia (arrow), adjacent to the duodenum (D), which also shows an air-fluid level. b More distally in the same patient, the cause of the obstruction is seen with a dependent filling defect (arrowhead) in the distal CBD in keeping with a stone. This should not be confused with the non-dependent aerobilia also shown at this level (arrow). c Axial T2-weighted MRI in a different patient shows a central filling defect in a dilated CBD which is due to flow artefact (arrow). The patient also has chronic cholecystitis with a contracted gallbladder (arrowheads)