Nuclear Medicine Guide

NucMedNet Online Physicians’ Guide

Hepatobiliary Imaging Clinical Synopsis Robert E. Henkin, MD, FACNP, FACR, Editor Clinically, ultrasound is often the first diagnostic test emINTRODUCTION ployed. When gallstones are identified or dilatation of Biliary tract disease occurs in approximately 20 million the common duct is noted, the diagnosis is considered to Americans each year. As a result of this disease, apbe made. CT has an accuracy similar to ultrasound. proximately 15 million patients will develop obstruction When one examines the specificity of these examiof the cystic duct. These patients may present with signs nations, the nuclear medicine study has the highest value. of epigastric or right-upper-quadrant pain, fever, and nauThe specificity of ultrasound examinations is variously sea. Various blood tests may be abnormal in this group reported as 60% to 64%. The specificity quoted in the as well. While the classical appearance of biliary tract literature for nuclear medicine hepatobiliary studies is 93% disease is well known, there are a number of other entito 96%. The positive predictive value of the nuclear ties that mimic this disease process. Heart disease, pneumedicine examination is as high as 90% in some series. monia, renal colic, and intestinal obstruction may present For ultrasound examinations, in the with a similar symptom complex. same patient population, only a As with all clinical evalua“When one examines the specificity 40% to 50% positive predictive tions, a complete history and of these [CT, nuclear medicine, and value is reported. The negative physical examination will permit ultrasound] examinations, the predictive value of nuclear medithe exclusion of a number of the nuclear medicine study has the cine studies has been reported to alternative diagnoses. Over the be as high as 99%. years, various laboratory and imhighest values.” aging tests have been devised to assist the clinician in separating those patients with bilPATIENT PREPARATION iary tract disease from those with other diseases. UltraPatient preparation involves keeping the patient in a fastsound studies of the gallbladder, computed tomography ing state for at least 4 to 8 hours prior to the study. Be(CT), and conventional x-rays have all been employed to ginning a study too soon after feeding may result in a make a diagnosis in this patient group. With this array of false negative study since the gallbladder may recently examinations available, many physicians make an arbihave emptied and is not filling at the time of the study. trary choice as to which technique they will employ. There Patients who have not eaten for more than 48 hours may are significant differences between diagnostic ultrasound, also have a false negative study. The gallbladder, when CT, and nuclear medicine examinations with regard to put at rest by fasting for 48 or more hours, may not be the accuracy in various biliary tract conditions. visualized on the study. Hyperalimentation patients may also have nonvisualization of the gallbladder. Some auCOMPARISON OF DIAGNOSTIC TESTS thors have recommended the use of a CCK analog to Nuclear medicine examinations are considered to have force the gallbladder to empty completely and then refill. In some cases this may be of benefit. the highest sensitivity, in excess of 95%. In the same There are a group of patients who have fasted for a patient population with gallbladder disease, ultrasonograprolonged period in whom the gallbladder does not fill phy has a reported sensitivity of 80%. One of the facspontaneously. In this group of patients the use of intrators that may lead to the use of ultrasound instead of the venous morphine may lead to gallbladder filling. Mornuclear examination, despite its increased sensitivity, is phine causes spasm of the sphincter of Oddi. This rethat ultrasound can image other abdominal organs as well.

sults in an increase in back pressure throughout the duct system from the spasm and forces bile into the cystic duct. This maneuver is generally performed at 15 to 30 minutes post injection so that sufficient activity remains in the liver to fill the gallbladder. The use of morphine in patients who do not have gallbladder visualization reduces the false positive study rate. If the patient is unable to receive morphine, repeated images should be performed for at least four hours post injection. Failure to visualize the gallbladder by four hours is considered evidence of cystic duct obstruction in patients with otherwise normal liver function.

THE NORMAL STUDY Normal nuclear medicine biliary tract studies demonstrate the gallbladder and common duct by 30 to 60 minutes post injection. Ideally, activity should be identified in the GI track within one hour of the intravenous administration of the radiopharmaceutical. (Figure 1) Between 1 and 2 hours post injection normal patients will show essentially complete emptying of the liver. Retained activity in the liver beyond two hours suggests hepatic dysfunction. Diseases such as hepatitis and cholestasis may present with retained activity in the liver. When the disease process is moderate to mild, further delayed imaging may demonstrate the gallbladder and duct system. At times, imaging as late as 24 hours may be required. NONOBSTRUCTIVE BILIARY TRACT DISEASE While the nuclear medicine hepatobiliary study is highly accurate at determining acute cholecystitis, it is often used to evaluate a different patient group. Some patients present with right-upper-quadrant pain that mimics the symptoms of gallbladder disease. However, the ultrasound and x-ray examinations reveal no evidence of gallstones in these patients. This entity has been variously dubbed acalculous cholecystitis or biliary dyskinesia. This is felt to represent an end organ defect with regard to CCK response. The surgical literature contains patient outcome data that shows when a blind cholecystectomy is performed, only 50% of these patients experience relief of symptoms. In order to evaluate this patient population an interventional hepatobiliary tract study is performed. Once the gallbladder is clearly visualized, the patient is given a small dose, .02 to .04 micrograms per kilogram, of CCK. The nuclear scan continues after the injection. The patient is observed for replication of the clinical symptoms. If the patient experiences abdominal discomfort similar

Fig 1. Normal nuclear medicine biliary tract study at 15 to 20 minutes post injection. IHBD–intrahepatic bile duct;GB–gallbladder; CBD–common bile duct.

to that he or she had noted previously, the test is considered to be positive. In addition to the clinical observation, a computation is performed to measure the gallbladder ejection fraction. In a normal patient, greater than 50% of the gallbladder’s contents will be ejected by 15 minutes after CCK injection. In those patients who fail to eject 40% or more of its contents after CCK, it is highly likely that they will benefit from surgery (Figure 2). Ejection fractions between 40% and 50% are indeterminate. However, if the clinical symptoms were replicated and the ejection fraction is below 50%, there is high probability the patient will benefit from a cholecystectomy. The literature has demonstrated that as high as an 80% to 90% success rate is achieved in patients with positive CCK nuclear studies.

Fig 2. Abnormal gallbladder ejection fraction after CCK analog administration. This patient should benefit from surgery.

BILE LEAKAGE

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Patients who have experienced blunt abdominal trauma or who may have undergone recent abdominal surgery can develop bile leaks. Such leaks are clinically devastating. Often, surgical inspection of the abdomen cannot accurately localize the leak. One of the applications of hepatobiliary imaging is the detection of such leaks. Because the radiopharmaceutical administered mimics the bile pathway, it is excreted in the bile. By continuous imaging post injection, the site of leakage can be identified (Figure 3). Correlation with anatomic imaging modalities, such as ultrasound or CT, is suggested to identify the location of the gallbladder.

Fig 4. Patient with a fistula between the gallbladder and colon. (Arrow–colon)

Patients with biliary dyskinesia are routinely identified by a CCK-augmented nuclear scan. A higher percentage of patients with biliary dyskinesia will benefit from surgery if they are selected using the hepatobiliary scan criteria. Patients with suspected bile leaks or fistulas may have the site of leakage localized by the nuclear study. Nuclear hepatobiliary studies are available in virtually any hospital offering acute care services.

REFERENCES

Fig 3. Automobile accident victim who suffered a hepatic laceration. Postop he developed bile peritonitis. Note the leakage of bile from the laceration site in the dome of the right lobe.

In some patients spontaneous or postoperative fistulas from the gallbladder may result. Hepatobiliary imaging may be used in this population to demonstrate the precise site of communication. The information obtained is used to plan the corrective surgical procedure (Figure 4).

SUMMARY Hepatobiliary imaging is a highly accurate nuclear medicine technique for vizualizing the gallbladder and bile duct system. Clinically, the ultrasound examination is usually the first procedure employed in evaluating the gallbladder. However, inconclusive ultrasound examinations should be followed by a nuclear medicine study.

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