Hepatobiliary transport
The tracer is taken into the hepatocyte on the same transporter that handles bilirubin and pumped out into the bile canaliculus unchanged. Because it is a transit study, the diagnosis lives in the timing.
A normal sequence is hepatic uptake by five minutes and gallbladder plus duodenal activity by sixty. Non-visualisation of the gallbladder at sixty minutes — confirmed at four hours or after morphine, which raises intraluminal pressure by contracting the sphincter of Oddi — is cystic duct obstruction, and the study is close to 100% sensitive for acute cholecystitis.
The competition with bilirubin sets the failure mode. Mebrofenin, with about 98% hepatic extraction, works up to a bilirubin of roughly 20–30 mg/dL; disofenin is close behind, and it was the older lidofenin that gave up early. Hepatic uptake with no biliary excretion is hepatocellular dysfunction, not obstruction, and it is a different report.
The agents
Tc-99m mebrofenin / disofeninHIDA · Choletec, Hepatolite
SPECT / planarTc-99m · t½ 6.01 h · iminodiacetic acid analogues
- Handle
- OATP1B1/1B3 for uptake, MRP2 for canalicular excretion
- Trapping
- Taken into the hepatocyte and pumped into bile unchanged. Normal transit: liver by 5 min, gallbladder and duodenum by 60 min.
- Use
- Acute cholecystitis; biliary atresia versus neonatal hepatitis after five days of phenobarbital; bile leak; gallbladder ejection fraction with CCK for chronic acalculous cholecystitis (consensus lower limit of normal 38% with a 60-minute sincalide infusion); sphincter of Oddi dysfunction; post-surgical and biliary-enteric anatomy.
- Pitfall
- Bilirubin competes at the uptake step. Mebrofenin has the highest hepatic extraction (~98%) and stays diagnostic to a bilirubin of 20–30 mg/dL; disofenin (~89%) is close behind, while the older lidofenin failed above about 5 mg/dL. Fasting over 24 hours or TPN gives a viscous, full gallbladder that will not fill: pretreat with CCK. A recent meal gives a contracted gallbladder that also will not fill: fast 4 hours. The rim sign — increased pericholecystic hepatic activity — suggests gangrenous cholecystitis. Hepatic uptake without biliary excretion is hepatocellular dysfunction, not obstruction.