Hepatobiliary Scan (HIDA)
The hepatobiliary scan (HIDA scan, cholescintigraphy) follows bile from the liver to the gallbladder, bile ducts and small bowel. It uses technetium-99m labelled hepatobiliary iminodiacetic acid compounds (mebrofenin is the usual agent), which are taken up by hepatocytes in the same way as bilirubin and excreted into bile without conjugation.
The adult dose is 150 to 300 MBq intravenously, and children receive a weight based dose with a minimum of about 20 MBq.
The camera is placed over the upper abdomen, and images are taken at 1 minute for 60 minutes, with extra images at 2 to 4 hours or 24 hours when needed.
Additional steps are added for the question. Sincalide (a synthetic cholecystokinin) measures gallbladder emptying. Morphine (about 0.04 mg for each kg) raises pressure in the bile duct and fills the gallbladder in acute cholecystitis.
Phenobarbital is given for 5 days before a study in suspected biliary atresia. The effective dose is about 3 to 5 mSv.
Gallstones affect 10 to 15% of adults, and 20% of those develop acute cholecystitis. The scan has a sensitivity and specificity of about 90 to 95% for acute cholecystitis, and is more accurate than ultrasound when the ultrasound is equivocal.
It is the best test for bile leak and for biliary atresia in infants with prolonged jaundice.
Indications.
- Acute cholecystitis when ultrasound is equivocal (cystic duct obstruction).
- Acalculous cholecystitis in critically ill patients.
- Chronic acalculous gallbladder disease: low gallbladder ejection fraction in biliary type pain with normal ultrasound.
- Bile leak after cholecystectomy, liver surgery, transplant or trauma.
- Biliary atresia versus neonatal hepatitis in infants with persistent conjugated jaundice.
- Choledochal cyst and other congenital biliary anomalies.
- Sphincter of Oddi dysfunction and bile duct obstruction (partial or complete).
- Patency of biliary enteric anastomoses and liver transplant biliary complications.
- Enterogastric (bile) reflux after gastric surgery.
- Hepatic function in segments, before liver resection (in selected centres).
Contraindications and precautions.
- Pregnancy: avoid unless essential. Breast feeding: a brief interruption as the local rule requires.
- Fasting for 4 to 6 hours before the study, so that the gallbladder is not contracted. Fasting for over 24 hours (or total parenteral nutrition) fills the gallbladder with viscous bile and causes false positives. Pre-treatment with sincalide is used in those cases.
- Recent meal within 4 hours causes a false positive.
- Opioids are stopped for at least 6 hours, because they cause spasm of the sphincter of Oddi. This is not needed for the morphine augmented method.
- Serum bilirubin over about 100 to 150 micromol/L (6 to 9 mg/dL) reduces hepatic uptake, and delayed images or a higher dose are used.
- Sincalide: caution in severe gallbladder disease, and in pregnancy. Nausea, cramps and flushing occur and settle.
- Morphine: respiratory depression, allergy and biliary pain. Naloxone is available.
Preparation and technique.
The patient lies supine. The field of view includes the liver, gallbladder, bile ducts and small bowel. Anterior images are taken at 1 minute for 60 minutes, and a right lateral view is added to separate the gallbladder from the bowel and duodenum.
The usual time for gallbladder filling is 30 to 60 minutes. If the gallbladder is not seen at 60 minutes while bowel activity is present, morphine is given, with 30 minutes more imaging, or delayed images are taken at 3 to 4 hours.
For ejection fraction, sincalide 0.02 microgram for each kg is infused over 30 to 60 minutes after the gallbladder has filled, and the fraction emptied is calculated from the counts. The infusion over 60 minutes gives more reproducible results than a bolus.
In infants, phenobarbital 5 mg for each kg daily is given for 5 days before the study to raise bile excretion, and images are taken at 5 minutes, hourly up to 6 hours and at 24 hours.
