<s>[INST] context: The plain films demonstrate dilated stomach and proximal loops of bowel. The cross-table upper GI demonstrates a "curly Q" twist of barium as it passes through the malrotated portion of bowel. Malrotation results when incomplete rotation of the intestines occurs during embryologic development. The most common type of malrotation is failure of the cecum to move to its correct location in the right lower quadrant. Most patients present in the first weeks of life with bilious vomiting indicative of bowel obstruction and/or intermittent abdominal pain. Acute presentation, similar to that in the question, is caused by a volvulus of the intestines. The diagnosis is confirmed by radiographs; barium contrast studies (upper GI and/or enema) demonstrate malposition of the cecum in the vast majority of cases. Treatment is surgical. Appendicitis is rare at this age and presents as an acute, rigid abdomen and signs of sepsis. Pyloric stenosis usually does not occur until after 3 weeks of life and presents with nonbilious vomiting. If the child were 6 months or older, intussusception would be higher on the differential, but it is an unusual condition for this age. Jejunal atresia would have been noted on the first day of life, as the patient would not have tolerated any feeds prior to newborn discharge. [/INST] question: A 1-week-old previously healthy infant presents to the emergency room with the acute onset of bilious vomiting. The abdominal plain film in the emergency department (A) and the barium enema done after admission (B) are shown. Which of the following is the most likely diagnosis for this patient? | options: A: Jejunal atresia B: Hypertrophic pyloric stenosis C: Malrotation with volvulus D: Acute appendicitis | answer: C </s>