C

Failure to visualize the gallbladder on a hepatobiliary (HIDA) scan reflects cystic-duct obstruction, the hallmark of acute calculous cholecystitis; studies show that every patient with persistent non-visualization had acute cholecystitis, while normal subjects always filled the gallbladder [Paré et al., 1978, PMID 630497]. Gallstones obstructing the common bile duct still allow tracer to reach the gallbladder, and chronic or neoplastic disease more often shows delayed or partial, not absent, filling.