What is the primary investigation used to assess for biliary atresia?

The primary investigation used to assess biliary atresia is abdominal ultrasound. This imaging technique is particularly effective in evaluating the biliary system in infants. An abdominal ultrasound can reveal the absence or abnormality of the gallbladder and can also assess the intrahepatic and extrahepatic bile ducts.

Ultrasound is non-invasive, does not involve radiation, and provides real-time imaging which is crucial for identifying structural anomalies. In cases of suspected biliary atresia, an ultrasound can help differentiate between other conditions such as choledochal cysts or liver diseases by looking for specific markers, such as the "triangular cord sign," which indicates obliterated bile ducts.

Other imaging modalities, like magnetic resonance imaging and computed tomography, are less commonly used in this clinical context due to their higher costs, longer procedural times, and exposure to radiation in the case of CT scans. Liver biopsy, while useful in diagnosing liver pathology, is not a first-line investigation for biliary atresia, as it does not provide information about the anatomy of the bile ducts.

Therefore, abdominal ultrasound stands out as the primary tool for the initial assessment of biliary atresia, guiding further management decisions based on the findings.