A hepatobiliary iminodiacetic acid (HIDA) scan is an imaging procedure used to evaluate the function of the liver, gallbladder, and bile ducts. This diagnostic tool assesses how bile flows through the biliary system, from its production in the liver to its release into the small intestine. Its primary purpose is to identify issues like inflammation, blockages, or improper function within this digestive pathway.
How a HIDA Scan Works
A HIDA scan begins with the intravenous injection of a radioactive tracer into a vein in the patient’s arm. This tracer travels through the bloodstream, is selectively absorbed by the liver’s bile-producing cells, and mixes with bile, following its natural path through the biliary system.
A specialized camera, called a gamma camera, is positioned over the patient’s abdomen to track the tracer’s movement. This camera detects the gamma rays emitted by the tracer, creating images that show how the tracer flows from the liver, into the bile ducts, gallbladder, and small intestine. The imaging process typically takes one to two hours. During the scan, a medication called sincalide (cholecystokinin or CCK) might be administered to stimulate the gallbladder to contract and empty, which helps evaluate its function.
What Normal HIDA Scan Results Show
In a healthy individual, a HIDA scan demonstrates prompt movement of the radioactive tracer throughout the biliary system. The tracer first appears in the liver, followed by rapid uptake into the bile ducts. The gallbladder is typically visualized within one hour of the tracer injection, indicating that the cystic duct, which connects the gallbladder to the main bile duct, is open and functioning.
Following the gallbladder’s visualization, the tracer then progresses into the small intestine, confirming that the bile ducts are clear and allowing bile to flow into the digestive tract. When sincalide is administered to stimulate gallbladder contraction, a normal gallbladder ejection fraction (GBEF) is calculated. A GBEF at or above 35% indicates that the gallbladder efficiently empties its contents.
Interpreting Abnormal Findings
Abnormal HIDA scan results can pinpoint specific issues within the biliary system, guiding diagnosis and treatment. Each distinct finding corresponds to a particular condition affecting the liver, gallbladder, or bile ducts.
Non-visualization of the Gallbladder
Non-visualization of the gallbladder, especially if it occurs within four hours of tracer injection or after morphine administration, strongly suggests acute cholecystitis. This acute inflammation is often caused by a blockage in the cystic duct, preventing tracer entry. This lack of visualization is a highly reliable sign for this condition.
Low Gallbladder Ejection Fraction (GBEF)
A low gallbladder ejection fraction (GBEF) suggests chronic cholecystitis or biliary dyskinesia. If the GBEF is less than 35%, it indicates that the gallbladder is not contracting effectively to empty bile, which can lead to symptoms like pain, even without the presence of gallstones. A very high GBEF (80% or greater) may also be considered abnormal, indicating a hyperkinetic gallbladder that contracts too forcefully, leading to similar symptoms.
Biliary Obstruction
If the radioactive tracer fails to reach the small intestine, or its movement is significantly delayed, it points to a biliary obstruction. This blockage usually occurs in the common bile duct, preventing bile from flowing into the digestive system. Such an obstruction can be caused by gallstones, strictures, or other conditions. The scan visualizes this impaired flow, highlighting the location of the impediment.
Sphincter of Oddi Dysfunction
Delayed emptying of the tracer from the bile ducts into the small intestine, without a clear physical obstruction, may indicate Sphincter of Oddi dysfunction. This condition involves a spasm or improper relaxation of the muscular valve that controls bile and pancreatic fluid flow into the duodenum. The HIDA scan can show a backup of the tracer in the bile ducts due to this functional problem.
Factors That Can Affect Results
Several factors can influence HIDA scan results. Prolonged fasting before the scan, exceeding the recommended four hours, can cause the gallbladder to be overly filled and less responsive to stimulation. This can result in a falsely low gallbladder ejection fraction or even non-visualization, mimicking an underlying problem.
Certain medications can also interfere with the scan’s accuracy. Opioid pain medications, for example, are known to cause spasms of the Sphincter of Oddi. This spasm can lead to delayed tracer entry into the intestine, suggesting a blockage where none exists. Liver disease can significantly impact the scan because the liver is responsible for taking up and excreting the tracer. Impaired liver function can lead to delayed tracer uptake, poor visualization of the biliary system, or non-visualization of the gallbladder, requiring extended imaging times.
Understanding Your Results with Your Doctor
While this information provides a general understanding of HIDA scan results, the definitive interpretation must come from a qualified healthcare professional. Your doctor will consider the scan’s findings in conjunction with your specific symptoms, medical history, and the results of any other diagnostic tests. This comprehensive approach ensures an accurate diagnosis and appropriate treatment plan.
Prepare questions for your doctor regarding your HIDA scan results. Inquire about the specific implications of your findings, potential underlying causes, and any further tests or treatments that may be recommended. Your healthcare provider is the best resource for clarifying complex medical information and guiding your next steps.