Hepatobiliary Imaging — USG, CT

A 52-year-old woman from Mumbai presents with a 3-month history of progressive right upper quadrant pain, weight loss of 4 kg, and low-grade fever. On examination, she is icteric with a palpable gallbladder. Laboratory investigations show total bilirubin 4.2 mg/dL, direct bilirubin 3.8 mg/dL, and alkaline phosphatase 320 IU/L. Transabdominal ultrasound reveals a thick-walled gallbladder with a large stone impacted at the neck, dilated intrahepatic bile ducts, and a hypoechoic mass in the gallbladder fundus that does not move with position change. What is the most likely diagnosis?

A 38-year-old man from Delhi presents with a 2-week history of right upper quadrant pain, nausea, and dark urine. He denies fever. On examination, he is mildly icteric. Laboratory tests show total bilirubin 3.5 mg/dL, direct bilirubin 2.8 mg/dL, ALT 280 IU/L, AST 240 IU/L, and alkaline phosphatase 180 IU/L. Transabdominal ultrasound shows a normal-sized gallbladder with no stones, normal liver echotexture, and no intrahepatic bile duct dilatation. The common bile duct measures 8 mm in diameter. Magnetic resonance cholangiopancreatography (MRCP) reveals a 12 mm filling defect within the distal common bile duct with proximal duct dilatation. What is the most likely diagnosis?

A 58-year-old man from Delhi presents with painless jaundice and pruritus for 3 weeks. He denies fever or weight loss. On examination, he has icterus and a palpable gallbladder. Abdominal ultrasound shows a dilated common bile duct (CBD) measuring 12 mm with an abrupt transition point at the pancreatic head. The gallbladder is distended but contains no stones. What is the most likely diagnosis?

A 42-year-old woman from Mumbai presents with acute RUQ pain, fever (38.5°C), and jaundice for 2 days. Laboratory values: WBC 14,000/μL, ALT 320 U/L, AST 280 U/L, bilirubin 4.2 mg/dL, ALP 180 U/L. Abdominal ultrasound shows a thickened gallbladder wall (5 mm), pericholecystic fluid, multiple echogenic foci within the gallbladder lumen with acoustic shadowing, and a dilated CBD (10 mm) with an echogenic focus impacted at the ampulla. What is the most likely diagnosis?

On contrast-enhanced CT, which imaging feature is most specific for diagnosing hepatic steatosis?