What HIDA scan finding is indicative of acute cholecystitis?

In the context of diagnosing acute cholecystitis, the finding that indicates the condition is the absence of gallbladder filling on a HIDA scan after 4 hours. Acute cholecystitis is typically caused by obstruction of the cystic duct, often due to gallstones, which leads to inflammation and subsequent ischemia of the gallbladder.

In a HIDA scan, a radiotracer is injected into the patient, and its movement through the hepatobiliary system is observed. In cases of acute cholecystitis, because of the blockage, the gallbladder does not fill with the tracer, which can be seen as an absent filling after a designated period, such as 4 hours. This finding is critical in differentiating acute cholecystitis from other conditions, like chronic cholecystitis or issues related to liver function.

The other findings—such as seeing gallbladder filling or presence of tracer in the bile ducts—do not suggest acute cholecystitis. Rapid filling would indicate normal gallbladder function, incompatible with the diagnosis of acute cholecystitis. Thus, the absence of gallbladder filling serves as a definitive indicator of the acute inflammatory process occurring