<prompt> Answer this question truthfullyWhich cause of bilious vomiting is characterized by the obstruction of the ileum by meconium with a microcolon visualized on X-ray?  <response>: <reason> Meconium ileus usually secondary to cystic fibrosis is the cause of bilious vomiting that is characterized by the obstruction of the ileum by meconium with a microcolon visualized on X-ray. 