Question

A $52$-year-old female presents to the emergency department with a two-day history of intermittent, severe right upper quadrant abdominal pain that radiates to her right shoulder. She also reports nausea and multiple episodes of non-bilious vomiting. On physical examination, her temperature is $37.1^\circ$ C ($98.8^\circ$ F), blood pressure is $128/82$ mmHg, heart rate is $88$/min, and respiratory rate is $14$/min. She has scleral icterus and localized tenderness to palpation in the right upper quadrant without rebound or guarding. Laboratory studies reveal:

White blood cell count: $8,500$/mm $^3$
Total bilirubin: $2.6$ mg/dL
Direct bilirubin: $1.9$ mg/dL
Aspartate aminotransferase (AST): $190$ U/L
Alanine aminotransferase (ALT): $215$ U/L
Alkaline phosphatase: $410$ U/L

A transabdominal ultrasound demonstrates cholelithiasis and a common bile duct measuring $10$ mm in diameter. No echogenic shadowing structures are visualized within the common bile duct. Which of the following is the most appropriate next step in the diagnostic workup of this patient?