HIDA (Hepatobiliary Iminodiacetic Acid) Scan


A Hepatobiliary Iminodiacetic Acid (HIDA) scan, also known as cholescintigraphy, is a nuclear imaging procedure used to evaluate the function of the liver, gallbladder, bile ducts, and small intestine. It involves using a radioactive tracer to visualize the flow of bile from the liver to the small intestine.

Indications

A HIDA scan is typically indicated for the following conditions:

  1. Acute Cholecystitis: To diagnose inflammation of the gallbladder.
  2. Chronic Cholecystitis: To evaluate chronic gallbladder disease.
  3. Bile Duct Obstruction: To detect blockages in the bile ducts.
  4. Biliary Atresia: To assess bile duct abnormalities in infants.
  5. Postoperative Bile Leaks: To detect leaks after gallbladder surgery.
  6. Gallbladder Ejection Fraction: To measure how well the gallbladder empties bile.

Procedure

  1. Preparation:
    • Fasting for 4-6 hours before the test is usually required.
    • Medications may need to be adjusted or withheld prior to the test.
    • Allergies to the radioactive tracer or contrast agents should be noted.
  2. Tracer Injection:
    • A radioactive tracer (usually technetium-99m labelled with HIDA) is injected intravenously.
    • The tracer is taken up by the liver and excreted into the bile.
  3. Imaging:
    • The patient lies on a table under a gamma camera.
    • Sequential images are taken over a period (usually 1-2 hours) to track the movement of the tracer through the hepatobiliary system.
    • The patient may be given a fatty meal or a medication such as cholecystokinin (CCK) to stimulate gallbladder contraction.

Interpretation of Results

  1. Normal Findings:
    • The tracer flows from the liver into the bile ducts, fills the gallbladder, and eventually moves into the small intestine within a specified timeframe (usually within 60 minutes).
  2. Acute Cholecystitis:
    • Non-visualization of the gallbladder due to cystic duct obstruction, even after 4 hours, indicates acute cholecystitis.
  3. Chronic Cholecystitis:
    • Delayed visualization of the gallbladder or reduced gallbladder ejection fraction suggests chronic cholecystitis.
  4. Bile Duct Obstruction:
    • Non-visualization of the small intestine and dilated bile ducts may indicate a common bile duct obstruction.
  5. Biliary Atresia:
    • Non-visualization of bile ducts in infants suggests biliary atresia.
  6. Bile Leak:
    • Abnormal accumulation of tracer outside the biliary system may indicate a bile leak.

Advantages and Limitations

Advantages

  • Functional Assessment: This technique provides functional information about the gallbladder and biliary system that other imaging techniques, like ultrasound, cannot.
  • Non-Invasive: Minimally invasive with relatively low radiation exposure.
  • Diagnostic Clarity: Useful for diagnosing conditions where other imaging modalities are inconclusive.

Limitations

  • Radiation Exposure: Though low, there is some radiation exposure.
  • Allergic Reactions: Possible but rare allergic reactions to the radioactive tracer.
  • Limited Structural Detail: This does not provide detailed anatomical images compared to CT or MRI.
  • Fasting Requirement: Requires patient compliance with fasting instructions.

Complications

Complications are rare but may include:

  • Allergic reactions to the radioactive tracer.
  • Pain or discomfort at the injection site.
  • Rarely, nausea or vomiting, especially if CCK is administered.

Summary

The HIDA scan is a valuable diagnostic tool for assessing the function and pathology of the hepatobiliary system. It is particularly useful for diagnosing acute and chronic cholecystitis, bile duct obstructions, biliary atresia in infants, and postoperative bile leaks. Proper patient preparation and understanding of the procedure enhance its diagnostic accuracy and patient safety.