A HIDA scan is a specialized imaging procedure used to evaluate the liver and bile ducts, playing a significant role in diagnosing biliary atresia in infants. Biliary atresia is a rare, serious liver condition that affects newborns.
Understanding Biliary Atresia
Biliary atresia is characterized by blocked or absent bile ducts outside the liver. These ducts transport bile from the liver to the small intestine. When bile flow is obstructed, it accumulates in the liver, leading to cell damage and scarring. Without timely intervention, this can result in cirrhosis and liver failure.
Infants with biliary atresia often exhibit specific signs. A common symptom is persistent jaundice, with yellow or greenish skin and eyes, extending beyond typical newborn jaundice. Parents might also notice pale, clay-colored stools, dark urine, and an enlarged liver.
Early identification and treatment of biliary atresia are important for improving outcomes. The primary surgical treatment, the Kasai portoenterostomy, is most effective before significant liver damage, ideally within 60 to 90 days of life. If the Kasai procedure is unsuccessful or diagnosed too late, a liver transplant may be necessary.
The HIDA Scan Explained
A HIDA (Hepatobiliary Iminodiacetic Acid) scan is a nuclear medicine imaging test visualizing the liver, bile ducts, gallbladder, and small intestine. It helps assess liver function and bile flow. This non-invasive method shows how bile is produced and transported.
The scan uses a small amount of radioactive tracer, typically technetium-99m iminodiacetic acid (99mTc-IDA), injected into the infant’s bloodstream. This tracer behaves similarly to bilirubin, a bile component, and is taken up by liver cells. It then travels through the bile ducts, into the gallbladder, and into the small intestine.
A gamma camera captures the tracer’s movement, detecting gamma rays. By tracking its path, professionals observe if it flows freely through the bile ducts into the intestine. If the tracer does not reach the small intestine, it indicates a biliary system blockage, suggesting biliary atresia.
What to Expect During a HIDA Scan
Preparing an infant for a HIDA scan involves specific steps for accurate results. Infants typically fast for a few hours, though clear liquids may be allowed. Many infants suspected of biliary atresia may receive phenobarbital orally for three to five days prior. This pre-treatment, administered at 5 mg/kg per day in two divided doses, stimulates bile flow, enhancing tracer excretion and test clarity. The medical team decides this based on the infant’s condition.
During the scan, the radioactive tracer is administered through an intravenous (IV) line, usually in the infant’s arm or hand. The infant is positioned under the gamma camera. Stillness is important for clear images, so sedation may be used. The imaging process can take several hours, with initial images captured immediately after tracer injection, and delayed images sometimes acquired up to 24 hours later.
Parents often have concerns about radiation exposure. The amount of radioactive material used is very small, and the procedure is safe for infants. The benefits of an accurate diagnosis for biliary atresia outweigh the minimal risks of the low radiation dose. After the scan, the infant can resume normal activities, and the tracer naturally leaves the body.
Interpreting HIDA Scan Results and Next Steps
HIDA scan results provide important information regarding bile flow. If the tracer reaches the small intestine within 24 hours, it indicates open, functional bile ducts. This finding usually helps rule out biliary atresia as the cause of symptoms. Such a result suggests jaundice or other signs are likely due to other cholestasis conditions.
Conversely, if the tracer does not appear in the small intestine, it suggests a biliary system blockage. This abnormal finding suggests biliary atresia or another bile duct obstruction. While an abnormal HIDA scan points towards a blockage, it is not always definitive for biliary atresia alone, as other conditions can also cause impaired bile flow. Therefore, further diagnostic tests are necessary to confirm the diagnosis.
Following an abnormal HIDA scan, medical professionals often recommend additional procedures to confirm or rule out biliary atresia. These may include a liver biopsy, where a tissue sample is examined under a microscope, or an intraoperative cholangiogram, a surgical procedure to visualize the bile ducts. If biliary atresia is confirmed, the primary treatment is the Kasai portoenterostomy, a surgical intervention to restore bile flow. The infant’s care involves a multidisciplinary medical team to manage the condition and address long-term needs, including the possibility of a liver transplant if the Kasai procedure is not fully successful.