A 42-year-old woman has 2 days of right upper abdominal pain and itching. Three episodes have occurred in the last few months. No fever or vomiting. Examination shows scleral icterus. A mass is palpated in the right upper quadrant. Ultrasound shows no gallstones. CT shows a 5 cm cystic structure medial to the gallbladder. Next step?
A) Endoscopic retrograde cholangiopancreatography (ERCP)
B) Magnetic resonance cholangiopancreatography (MRCP)
C) Liver biopsy
D) Surgical exploration