This patient presents with fever, chills, anorexia, and right upper quadrant (RUQ) pain several weeks after hospitalization for sigmoid diverticulitis . A key complication of intra-abdominal infections such as diverticulitis is portal pylephlebitis with hepatic abscess formation , due to bacterial spread via the portal venous system. MCCQE objectives emphasize recognizing liver abscess as a delayed complication of intra-abdominal sepsis, particularly when new RUQ pain and fever develop after an initial abdominal infection.

The most appropriate initial imaging test to confirm this diagnosis is ultrasound of the abdomen , which can detect hepatic abscesses and guide further management. CT abdomen is also highly sensitive, but among the listed options, ultrasound is most appropriate.

Chest and abdominal radiographs are nonspecific. HIDA scan evaluates cystic duct obstruction in suspected acute cholecystitis, which is less likely given the recent diverticulitis and systemic features. ERCP is used for biliary obstruction or ascending cholangitis, typically associated with jaundice.

Thus, abdominal ultrasound is most likely to confirm a hepatic abscess.